B M 251 lib LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class NEW THEORIES IN ASTRONOMY NEW THEORIES IN ASTRONOMY BY WILLIAM STIRLING CIVIL ENGINEER E. & F. N. SPON, LIMITED, 57 HAYMARKET Hefo gorfe: SPON & CHAMBERLAIN, 123 LIBERTY STREET 1906 K TO THE READER. MR. WILLIAM STIRLING, Civil Engineer, who devoted the last years of his life to writing this work, was born in Kilmarnock, Scotland, his father being the Rev. Robert Stirling, D.D., of that city, and his brothers, the late Mr. Patrick Stirling and Mr. James Stirling, the well known engineers and designers of Locomotive Engines for the Great Northern and South Eastern Railways respectively. After completing his studies in Scotland he settled in South America, and was engaged as manager and con- structing engineer in important railway enterprises on the west coast, besides other concerns both in Peru and Chile ; his last work being the designing and construction of the railway from the port of Tocopilla on the Pacific Ocean to the Nitrate Fields of Toco in the interior, the property of the Anglo-Chilian and Nitrate Railway Company. He died in Lima, Peru, on the 7th October, 1900, much esteemed and respected, leaving the MS. of the present work behind him, which is now published as a tribute to his memory, and wish to put before those who are interested in the Science of Astronomy his theories to which he devoted so much thought. CONTENTS. PAGE INTRODUCTION. i CHAPTER I. The bases of modern astronomy. Their late formation . . . .18 Instruments and measures used by ancient astronomers .... 19 Weights and measures sought out by modern astronomers 20 Means employed to discover the density of the earth. Measuring by means of plummets not sufficiently exact ....... 20 Measurements with torsion and chemical balances more accurate . . 21 Sir George B. Airy's theory, and experiments at the Harton colliery . . 22 Results of experiments not reliable. Theory contrary to the Law of Attrac- tion .23 Proof by arithmetical calculation of its error ...... 24 Difficulties in comparing beats of pendulums at top and bottom of a mine . 26 The theory upheld by text-books without proper examination ... 27 Of a particle of matter within the shell of a hollow sphere. Not exempt from the law of Attraction . . . . . . . . 28 A particle so situated confronted with the law of the inverse square of distance from an attracting body. Remarks thereon ..... 29 It is not true that the attraction of a spherical shell is "zero" for a particle of matter within it ......... 31 CHAPTER II. The moon cannot have even an imaginary rotation on its axis, but is generally believed to have. Quotations to prove this . . , . 33 Proofs that there can be no rotation. The most confused assertion that there is rotation shown to be without foundations . . 35 A gin horse does not rotate on its axis in its revolution . . -37 A gin horse, or a substitute, driven instead of being a driver ... 38 Results of the wooden horse being driven by the mill .... 38 The same results produced by the revolution of the moon. Centrifugal force sufficient to drive air and water away from our side of the moon . . 39 That force not sufficient to drive them away from its other side ... 40 No one seems ever to have thought of centrifugal force in connection with air and water on the moon . . . . . . . . . 41 viii New Theories in Astronomy. PAGE Near approach made by Hansen to this notion . . . . 41 Far-fetched reasons given for the non-appearance of air and water . . 42 The moon must have both on the far-off hemisphere .... 44 Proofs of this deduced from its appearance at change . . . -44 Where the evidences of this may be seen if looked for at the right place. The centrifugal force shown to be insufficient to drive off even air, and less water, altogether from the moon ...... 45 The moon must have rotated on its axis at one period of its existence . 47 The want of polar compression no proof to the contrary .... 48 Want of proper study gives rise to extravagant conceptions, jumping at con- clusions, and formation of " curious theories " . .... 4$ CHAPTER III. Remarks on some of the principal cosmogonies. Ancient notions . . 49 The Nebular hypothesis of Laplace. Early opinions on it. Received into favour. Again condemned as erroneous . . . . . - . 5 Defects attributed to it as fatal. New cosmogonies advanced . . 5 1 Dr. Croll's collision, or impact, theory discussed . . . . -53 Dr. Braun's cosmogony examined ........ 59 M. Faye's " Origine du Monde " defined 61 Shown to be without proper foundation, confused, and in some parts contra- dictory ........... 65 Reference to other hypotheses not noticed. All more or less only variations on the nebular hypothesis ........ 7 Necessity for more particular examination into it . * . . . 71 CHAPTER IV. Preliminaries to analysis of the Nebular hypothesis . . . . .72 Definition of the hypothesis 73 Elements of solar system. Tables of dimensions and masses . . -75 Explanation of tables and density of Saturn ...... 78 Volume, density and mass of Saturn's rings, general remarks about them, and satellites to be made from them ...... 79 Future of Saturn's rings ......... 79 Notions about Saturn's satellites and their masses ..... 80 Nature of rings seemingly not well understood . . . . .81 Masses given to the satellites of Uranus and Neptune, Explanations of . 81 Volumes of the members of the solar system at density of water . . 82 CHAPTER V. Analysis of the Nebular Hypothesis. Separation from the nebula of the rings for the separate planets, etc. ........ 83 Excessive heat attributed to the nebula erroneous and impossible . . 84 Contents. ix PAGE Centigrade thermometer to be used for temperatures .... 85 Temperature of the nebula not far from absolute zero .... 86 Erroneous ideas about glowing gases produced by collisions of their atoms, or particles of cosmic matter in the form of vapours . . . .86 Separation of ring for Neptune. It could not have been thrown off in one mass, but in a sheet of cosmic matter ...... 87 Thickness and dimensions of the ring ....... 88 Uranian ring abandoned, and its dimensions ...... 89 Saturnian ring do. do. ...... 90 Jovian ring do. do. . . . . . .91 Asteroidal ring do. do. ...... 93 Martian ring do. do. ...... 94 Earth ring do. do. ...... 95 Venus ring do. do. ...... 96 Mercurian ring do. do. ...... 97 Residual mass. Condensation of Solar Nebula to various diameters, and relative temperatures and densities ....... 98 Unaccountable confusion in the mode of counting absolute temperature examined and explained. Negative 274 degrees of heat only equal 2 degrees of absolute temperature ....... 100 The Centigrade thermometric scale no better than any other, and cannot be made decimal .......... 103 The sun's account current with the Nebula drawn up and represented by Table III 104 CHAPTER VI. Analysis continued. Excessive heat of nebula involved condensation only at the surface. Proof that this was Laplace's idea .... loS Noteworthy that some astronomers still believe in excessive heat , . 109 Interdependence of temperature and pressure in gases and vapours. Collisions of atoms the source of heat no Conditions on which a nebula can be incandescent. Sir Robert Ball . .no No proper explanation yet given of incandescent or glowing gas , . 112 How matter was thrown off, or abandoned by the Jovian nebula . . 115 Division into rings of matter thrown off determined during contraction . 116 How direct rotary motion was determined by friction and collisions of particles . . . . . . . . . . .117 Saturn's rings going through the same process. Left to show process . . uS Form gradually assumed by nebulas. Cause of Saturn's square-shouldered appearance ........... 120 A lens-shaped nebula could not be formed by surface condensation . .120 Retrograde rotary motion of Neptune and Uranus, and revolution of their satellites recognised by Laplace as possible . . . . .121 Satellites of Mars. Rapid revolution of inner one may be accounted for . 123 Laplace's proportion of 4000 millions not reduced but enormously increased by discoveries of this century . . . . . . . .124 x New Theories in Astronomy. CHAPTER VII. PAGE Analysis continued. No contingent of heat could be imparted to any planet by the parent nebula . . . . . . . . .126 Only one degree of heat added to the nebula from the beginning till it had contracted to the density of - 1 th of an atmosphere . . . .127 Increase in temperature from o to possible average of 274 when condensed to 4,1 50, ooo miles in diameter ....... 127 Time when the sun could begin to act as sustainer of life and light anywhere. Temperature of space . . . . . . . . .128 The ether devised as carrier of light, heat, etc. etc. What effect it might have on the nebula ......... 129 First measure of its density, as far as we know . . . . . .130 The estimate too high. May be many times less . . . . 133 Return to the solar nebula at 63,232,000 miles in diameter . . .134 Plausible reason for the position of Neptune not conforming to Bode's Law. The ring being very wide had separated into two rings . .134 Bode's law reversed. Ideas suggested by it . . . . . -135 Rates of acceleration of revolution from one planet to another . . 137 Little possibility of there being a planet in the position assigned to Vulcan . 1 38 Densities of planets compared. Seem to point to differences in the mass of matter abandoned by the nebula at different periods . . . .138 Giving rise to the continuous sheet of matter separating into different masses. Probably the rings had to arrive at a certain stage of density before con- tracting circumferentially . . . . . . . 139 Possible average temperature of the sun at the present day. Centra] heat probably very much greater . . . . . . . .140 Churning of matter going on in the interior of the sun, caused by unequal rotation between the equator and the poles . . . . .140 CHAPTER VIII. Inquiry into the Interior Construction of the Earth. What is really known of the exterior or surface . . . . . . . . .142 What is known of the interior . . .' . . . . .143 Little to be learned from Geology, which reaches very few miles down . 144 Various notions of the interior . . . . . . . .145 What is learnt from earthquake and volcanoes. Igno-aqueous fusion, liquid magma. ........... 146 Generally believed that the earth consists of solid matter to the centre. Mean density. Surface density ....... 147 More detailed estimate of densities near the surface ..... 148 Causes of increased surface density after the crust was formed . . .148 Calculations of densities for 9 miles deep, and from there to the centre forming Table IV 150 Reflections on the results of the calculations . . . . . .151 Notion that the centre is composed of the heaviest metals. " Sorting-out" theory absurd . . . . . . . . . I 5 I Contents. xi PAGE Considerations as to how solid matter got to the centre .... 152 Gravitation might carry it there, but attraction could not . . . 153 How the earth could be made out of cosmic matter, meteorites or meteors . 154 CHAPTER IX. Inquiry into the Interior Construction of the Earth continued . . .165 The earth gasiform at one period. Density including the moon may have been 10) ^ 00 -th that of air. Must have been a hollow body. Proofs given 166 Division of the mass of the earth alone into two parts . . . .169 Division of the two masses at 817 miles from surface . . . .171 Reasons why the earth cannot be solid to the centre . . . . .172 Gasiform matter condensing in a cone leaves apex empty . . . 1 72 Proportions of the matter in a cone . . . . . 1 73 Calculations of the densities of the outer half of the hollow shell of the earth. Remarks upon the condensation . . . . . . .174 Calculations of inner half of the hollow shell . . . . . . 175 Remarks upon position of inner surface of the shell . . V. ' '.. .177 Calculations of the same . . . . . ... 179 CHAPTER X. Inquiry into the interior construction of the earth continued . . . 184 Density of 8 '8 times that of water still too high for the possible compression of the component matter of the earth as known to us . . .185 Reasons for this conclusion drawn from crushing strains of materials . .186 A limit to density shown thereby . . . . . . . .187 The greatest density need not exceed 6 * 24 of water . . . . .188 Gases shut up in the hollow centre. Their weight must so far diminish the conceded maximum of 6 ' 24 . . . . . . . .189 Density of inner half of earth at 3000 miles diameter. Greatest density may be less than 5 ' 833 of water . . ' . . . . . 190 Supposed pressure of inclosed gases very moderate ..... 191 Meaning of heat limit to density. Temperature of interior half of shell and inclosed gases must be equal . . . . . . . .193 State of the hollow interior . . . . . . . . .194 Results of the whole inquiry . . . . . . . 195 CHAPTER XI. The Earth. The idea entertained by some celebrated men, and others . 197 Difficulties of forming a sphere out of a lens-shaped nebula . . .199 Various studies of the earth's interior made for special purposes. Difficulty some people find in conceiving how the average density of little over 5 ' 66 can be possible, the earth being a hollow sphere . . . 200 xii New Theories in Astronomy. PAGE What is gained by its being a hollow shell . . . . . .201 Geological theories of the interior discussed. Volcanoes and earthquakes in relation to the interior ......... 202 Liquid matter on the interior surface of the shell, and gases in the hollow, better means for eruptions than magma layers ..... 206 Focal depths of earthquakes within reach of water, but not of lavas . . 207 Minute vesicles in granite filled with gases, oxygen and hydrogen, but not water ............ 209 The Moon. A small edition of the earth . . . . . .211 Rotation stopped. Convulsions and cataclysms caused thereby. Air, water, vapour driven off thereby to far-off hemisphere. Liquid matter in hollow interior would gravitate to the inside of the nearest hemisphere . .212 Form and dimensions during rotation. Altered form after it stopped . . 213 Agreeing very closely with Hansen's " curious theory " . . .214 CHAPTER XII. Some of the results arising from the sun's being a hollow sphere. . . 215 Repetition of the effects of condensation on the temperature of the nebula . 216 Ideas called up by the apparently anomalous increase of temperature . .217 How heat is carried from the sun to the earth . . . . . .218 The sun supposed to radiate heat only to bodies that can receive and hold it, and not to all space. The heat of the sun accumulated in a hot box to considerably beyond the boiling point of water . . . .219 The heat accumulated in this way supposed to be due to a peculiar function of the ether, as it is a fact that heat can be radiated from a cold to a hot body ........... 220 The sun must be gaseous, or rather gasiform, throughout. No matter in it solid or even liquid. Divisions and densities of shell . . . .221 The hollow centre filled with gases, whose mass naturally diminishes the mean density of the whole body ....... 222 The amount of this reduction so far defined. The presence of gases or vapours in the hollow a natural result of condensation ..... 223 The hollow centre filled with gases not incompatible with the sun's being a hollow sphere. The temperature at the centre may be anything, not depending on any law of gases ....... 223 Further exposition of hollow-sphere theory put off till after further develop- ment of the construction of the sun ....... 224 CHAPTER XIII. The ether. Its nature considered. Behaves like a gas . . . 226 Can be pumped out of a receiver . . . . . . . .227 Light and heat do not pass through a tube in vacua. Laboratory experiments examined ........... 228 Light and darkness in a partial vacuum, though high .... 229 Electricity not a carrying agent ........ 230 Why there are light and dark strata in a high vacuum .... 232 Contents. xiii PAGE The real carrying agent through a high vacuum is the residue of ether left in it. Digression to consider the aurora ...... 233 How air may be carried to extraordinary heights. Zones of air carried up are made luminous by electricity ....... 234 Comparison of this method with experiments quoted. .... 236 Experiment suggested to prove whether light passes freely through a vacuum tube ............ 237 The ether does not pervade all bodies freely ...... 238 It must be renounced altogether or acknowledged to be a material body, subject to expansion, condensation, heating or cooling . . . 239 How light and heat pass through glass ....... 239 Temperature of the ether variable. Zodiacal light, cause of ... 240 CHAPTER XIV. The ether considered and its nature explained. Further proofs given by Dr. Crookes's work, of its material substance ..... 244 Highest vacuum yet produced. Absorbents cannot absorb the ether . . 246 Dr. Crookes's definition of a gas. Not satisfactory. Why . . . 247 A fluid required to pump matter out of a vessel ..... 248 Gas as described by Dr. Crookes would not suit . . . . . 249 The ether the only elastic fluid we have. The only real gas, if it is a gas . 250 A possible measure of the density of the ether ...... 250 Causes of dark and light zones in high vacua . . . . . .251 The real conductor of light in a high vacuum ...... 252 How a vacuum tube glows, when electricity passes through it . . 254 Conclusions arrived at through foregoing discussions. .... 255 Some exhibitions of light explained ....... 256 Gases can be put in motion, but cannot move even themselves . . . 257 The ether shown to be attraction. And primitive matter also . . . 258 All chemical elements evolved from it. Its nature stated .... 259 Action at a distance explained by the ether and attraction being one and the same . . . . . . . . . . . . 259 CHAPTER XV. Construction of the solar system. Matter out of which it was formed . . 261 Domains of the sun out of which the matter was collected .... 262 Stars nearest to the sun. Table VII. showing distances .... 263 Remarks on Binary Stars. Table VIII. showing spheres of attraction between the sun and a very few ....... 265 Sirius actually our nearest neighbour. Form of the sun's domains of a very jagged nature ...... .... 266 Creation of matter for the nebulae, out of which the whole universe was elaborated. Beginning of construction ...... 267 The law of attraction begins to operate through the agency of evolution . 267 Form of the primitive solar nebula. The jagged peaks probably soon left behind in contraction ..... . 268 xiv New Theories in Astronomy. PAGE How the nebula contracted. Two views of the form it might take. Com- parison of the two forms, solid or hollow ...... 269 The hollow centre form adopted. The jagged peaks left behind . . 272 The nebula assuming a spherical form. Shreds, masses, crescents separated from one side .......... 273 Probable form of interior of nebula. Compared with envelopes in heads of some comets ........... 274 Reflections on the nebula being hollow. Opinions of others quoted . . 275 The matter of a sphere solid to the centre must be inert there . . .276 Further proofs of the nebula being hollow . . . . . . 277 How rotary motion was instituted ........ 278 Such a nebula might take one of two forms . . . . . .279 The form depending on the class of nebula. Planetary in the case of the solar system. A similar conception of how rotary motion could be instituted . 280 CHAPTER XVI. The sun's neighbours still exercise their attraction over him . . .282 Regions of greatest density in the 9 nebulae dealt with ; compared with the orbits of the planets made from them . . . . . .283 Results of comparison favourable to the theory ..... 287 Differences of size in the planets have arisen from variations in the quantity of matter accumulating on the nebulae ...... 289 Causes of the retrograde motions in Neptune, Uranus, and their satellites . 290 Probable causes of the anomalous position of Neptune . . . 292 Rises and falls in the densities and dimensions of the planet*, explained . 293 The form of the nebulae must have resembled a dumb-bell .... 295 More about rises and falls in densities ....... 296 Reason why the Asteroid nebula was the least dense of the system . . 297 Not necessary to revise the dimensions given to the 9 nebulae . . . 298 Causes of the anomalies in the dimensions, densities, etc., of the Earth and Venus 299 The strictly spherical form of the sun accounted for. But it may yet be varied ............ 299 Repetition that a spherical body could not be made from a lens-shaped nebula by attraction and condensation 300 CHAPTER XVII. Former compromises taken up and begun to be fulfilled . . 301 Estimates of the heat-power of the sun made only from gravitation hitherto . 302 Contraction and condensation of a nebula solid to the centre. Heat pro- duced from attraction as well as by gravitation . . 303 What quantity of heat is produced by a stone falling upon the earth . .. 304 Showing again that there is a difference between attraction and gravitation . 305 Contraction and condensation of a hollow-sphere nebula, in the same manner as the solid one . . 35 Contents. xv PAGE Differences of rotation would be greater in a hollow nebula ; because a great deal of the matter would be almost motionless in a solid sphere . . 306 In neither case could matter be brought to rest, but only retarded in motion. Different periods of rotation accounted for ..... 307^ Table of different rates explained ........ 309 Heat produced by gravitation, attraction and churning, not all constituents of the heat-power of the sun . . . . . . . .310 There can be no matter in the sun so dense as water . . . . .311 The hollow part of the sun acting as a reservoir of gases, heat and pressure . 312 The behaviour of heat produced in the nebula, and its power . . . 313 How sun-spots are produced . . . . . . . . .314 Cyclonic motions observed in sun-spots. Why not all in certain directions, and why only observed in a very few . . . . . . 315 Cyclonic motions in prominences treated of . . . . .316 Many other things might be explained, on some of which we do not dare to venture. Concluding observations . . . . . . 317 CHAPTER XVIII. Return to the peaks abandoned by the original nebula. An idea of their number . . . . . . . . . . . 319 Example of their dimensions. What was made out of them - . . . 320 What could be made from one of them . . . . . . .321 How it could be divided into comets and meteor swarms .... 322 An example given. How a comet may rotate on its axis. And what might be explained thereby. Orbits and periods of revolution . . . 323 Not ejected from planets. Their true origin . . . . . . 324 Study of the velocities in orbit of comets, and results thereof . . . 326 How far comets may wander from the sun and return again . . .327 No reason why comets should wander from one sun to another. Confirma- tory of the description, in Chapter XV. of the sun's domains . . 328 Of the eternal evolution and involution of matter. The atmosphere and corona of the sun . . . . . . . . . . 329 Partial analogy between it and the earth's atmosphere . . . 331 The density of it near the sun's surface cannot be normally less than 28 atmo- spheres, but might be so partially and accidentally . -. . . 332 Probable causes of the enormous height of its atmosphere . . . 332 The mass taken into account, but cannot be valued . -. . . 334 Most probably no matter in the sun exceeds half the density of water. The unknown line in the spectrum of the corona belongs to the ether . . 335, NEW THEORIES IN ASTRONOMY. INTRODUCTION. THAT a little knowledge is a dangerous thing to the possessor, has been pointed out often enough, probably with the idea of keeping him quiet, but it is very certain that the warning has not always had the desired effect ; and in some respects it is perhaps much better that it has not, for it is sometimes the case that a little knowledge exhibited on an inappropriate occasion, or even wrongly applied, throws light upon some subject that was previously not very well understood. It sometimes happens that unconscious error leads to the dis- covery of what is right. The fact is, all knowledge is at first little, so that if the first possessor of it is kept quiet there is little chance of its ever increasing. On the other hand, much knowledge seems to be quite as ready to become dangerous on occasion, for it has sometimes led its possessor to fall into errors that can be easily pointed out, even by the possessor of little, if it is combined with ordinary intelligence. The possessor of much knowledge is apt to forget, in his keen desire to acquire more, that he has not examined with sufficient care all the steps by which he has attained to what he has got, and that by placing reliance on one false step he has erected for himself a structure that cannot stand ; or, what is worse per- haps, has prevented those who have followed him in implicit dependence on his attainments and fame from finding out the truth. If, then, both of these classes are liable to fall into error, there appears to be no good reason why one belonging to the first mentioned of them should absolutely refrain from making his ideas known, especially as he may thus induce B 2 New Theories in Astronomy. someone of the second to re-examine the foundations on which he has built up his knowledge. These reflections are in greater or lesser degree applicable to all knowledge and science of all kinds, even theological, in all their individual branches, and can be very easily shown to be both reasonable and true. And it may be added, or rather it is necessary to add, that every one of all the branches of all of them has a very manifest tendency towards despotism ; to impose its sway and way of thinking upon the whole world. At various intervals during the present century speculation has been indulged in, and more or less lively discussion has taken place about the great benefit it would confer on uni- versal humanity, were all the weights and measures of the whole earth arranged on the same standard. The universal standard proposed has been, of course, the metrical system, which had been elaborated by French savants who most pro- bably thought they had arrived at such a state of knowledge that they were able to establish the foundations of all science of all kinds and for all time, upon the most sure and most durable principles. These periods of metrical fever, so to speak, seem to come on without any apparent immediately exciting cause, and some people succumb to the disease, others do not, just the same as in the cases of cholera, influenza, plague, etc. Whether some species of inoculation for it may be discovered, or whether it will be found that an unlimited attack is really perfect health, will most probably be found out in the course of time, although it may be some centuries hence. What is of interest to under- stand at the present time is, what are the benefits to be derived from the proposed universal standard of weights and measures, and how they are to be attained. The principal and most imposing reason for its adoption is that it would be of immense service to scientific men all over the world, who would thus be able to understand the dis- courses, writings, discoveries, etc. of each other without the necessity of having to enter into calculations of any kind in order to be able to comprehend the arithmetical part of what they have listened to or read. Another argument brought forward in favour is, that it would greatly facilitate commercial Introduction. 3 transactions with foreign countries ; and it has been lately advanced that great loss is suffered by one country selling its goods, manufactured according to its own measures, in countries where the metrical system has been adopted. Yet another advantage held out is the convenience it would be to travellers in money matters ; but as this argument cannot be admitted without taking into consideration the necessity for one universal language all over the world, it has practically no place in any discussion on the subject, until the evil caused by the building of the Tower of Babel has been remedied. Not long after one of the periodical attacks of metric fever we came upon an essay written by J. J. Jeans on " England's Supremacy," and published in New York by Harper and Brothers, in 1886, in which we found the following: Numerical relation of occupations in England and Wales in 1881 : Professional 2*5 per cent. Commercial 3*7 per cent. Domestic 7*0 Industrial 24^5 Agricultural 5-3 In all 43-0 This statement shows that 43 per cent, of the whole popu- lation are occupied in some business or work of some kind, and leads us reasonably to suppose that the remaining 57 per cent, consist of women, children, and people who to put it short are non-producers ; the whole of whom can hardly be considered as much interested in the making of any alterations in the weights and measures of their country, rather the contrary, for they cannot expect to be much benefited by any change. The professional class naturally comprehends Theology, Law, Medicine, and Science generally, so that the 2*5 per cent, ascribed to it would be seriously reduced, if the advan- tage derived from the desired change were reckoned by the number really benefited by it. A similar reduction would have to be made on the 3*7 per cent, stated to be occupied in Commerce, as it is not to be supposed that the whole of the number are engaged in foreign trade. Thus the number of people in these two classes who might really reap some advan- B 2 4 New Theories in Astronomy. tage from the change, may be reduced by at least one half ; and if we consider that one person in ten of those occupied in the Agricultural and Industrial classes is a scientist we may pardon the Domestic class a very liberal allowance indeed, we arrive at the conclusion that 6 per cent, of the whole population might find, some more, some less, interest in the introduction into our country of the French metric system. The above statement refers only to England and Wales, but if Scotland and Ireland are added to them, the 6 per cent, proportion could not be very greatly altered : perhaps it would be less favourable to the change. Thus 94 per cent, or some- thing like 37 millions, of the whole population of the United Kingdom would be called upon to change their whole system of weights and measures, in order that 6 per cent, or somewhere between 2 and 2\ millions, should find some little alleviation in a part of their labours ; and surely 2 to 2j millions of scientists and merchants engaged in foreign trade is a very liberal allowance for the population of our country. If this does not show a tendency towards despotism, it would be hard to tell what it does show. Of course, it would not be fair to assume that the whole of the 6 per cent, would desire to see the proposed change carried into effect In all likelihood, a very considerable portion of the number would be disposed to count the cost of erecting such a structure before actually laying its foundations, and would refrain from beginning the work on considering by what means it was to be brought to a conclusion ; even without going so far as to find out that 94 per cent, of it at least would have to be done by forced labour. They might even go the length of speculating on how long it would take to coerce the 94 per cent into furnishing the forced labour, and on the hopelessness of the task. On the other hand, they might think it more natural to lay hold of the alternative of adopting a special system of weights and measures for the use of Science and Foreign Commerce alone, and leave the 94 per cent, to follow their own national and natural customs, which they would be very likely to do whatever might be determined, if we may judge by the progress made in France a century Introduction* 5 after the system was thought to be established. Very little opposition could be made to such a course, and if the best possible system were not adopted, the scientists would be the only parties put to inconvenience. They could improve and reform it, should they find it not to be perfect, without the necessity of coercing the 94 per cent, into furnishing another contingent of forced labour. But little is to be gained by saying any more about it. Should the metrical system be adopted some day by Act of Parliament, Science will have obtained what it has so long coveted, will be quite satisfied, and will trouble itself very little about how it affects the rest of the population. It will perhaps never even think of how India will be brought to buy and sell through the medium of the French Metrical S3 r stem. And now we have only one step to take on this subject. We may say that the project of establishing one standard of weights and measures for the whole world has a most unpleasant resemblance to the object proposed by the builders of the Tower of Babel ; the only thing that can be said in its favour being that it points towards an endeavour to do away with the bad results produced by that enterprise and to bring matters back to the state the world was in before the founda- tions of that celebrated edifice were laid. The foregoing is only one instance of the many that could be cited where science has schemed projects for universal progress without due thought, and has come to the conclusion that they could be easily carried out. There are as many examples of this jumping at conclusions as would fill many books, which of course it is not our purpose to do ; but there is one that it is necessary to have brought forward for exam- ination, because of its having, through a most incomprehensible want of thought, a tendency to establish Natural Religion on the very bases upon which the Christian Religion is estab- lished. The one referred to is that by which some of the most eminent scientists of the present century, following up what was done in former times, have been able by deep study and experiment, unfortunately coupled with unaccountable blind- 6 New Theories in Astronomy. ness or preconceived erroneous ideas, to formulate processes by which the whole universe may have elaborated itself from protyle and protoplasm, or some such substances which, without any foundation to build upon, they suppose to have existed from all eternity. This advance in science has been called the Theory of Evolution, and has been very generally considered to be new, or of comparatively very recent concep- tion ; but it is only a piece of the evidence of a very general propensity in those who come to acquire a little more know- ledge, to flatter themselves that they have power to seize hold of the Unknown. The theory may be new, but evolution most assuredly is not, as any one may convince himself who will take the trouble to read the first chapter of the Book of Genesis and to think. There he will find it stated that the earth and all things in it and on it were created and made in six days, or periods of time, showing him distinctly, if he does not shut his eyes wilfully, that two operations were employed in the process, one of creation and the other of making, which last can mean nothing but evolution. It does not matter a straw whether the latter operation was carried on personally by the Creator and Maker, or under the power of laws ordained by Him for the purpose ; it was evolution all the same, and just the kind of evolution the scientists above alluded to would have us believe to be new, not far from 3500 years after the account of the creation and making of the world was written by Moses. It will do no harm to take special notice of the work that was done in each of the six periods, as it will help to fix attention on the subject during examination and judgment ; and may even tend to open the eyes of any one who had made up his mind to keep them shut. In the first period the heavens and the earth were created, but the earth was without form and void, inanis et vacuus, according to The Vulgate (does that mean empty and hollow ?) and darkness was upon the face of the deep ; but light was let shine upon the earth to alternate with darkness, and between the two to establish day and night. It is there- fore evident that after the earth was created it had to be Introduction. 7 reduced to something like its present form, a globe of some kind, and to rotate on an axis, otherwise there could have been no alternations of light and darkness, of day and night. Where did the light come from ? Some people seem to think that Moses should have included a treatise on the creation and evolution of the universe, in his account of the work done in the first period of creation. For all that can be truly said to the contrary, he seems to have been quite as able to do so as any scientist of the present day ; but it is evident he thought it best to limit himself to writing only of the earth, as being of most interest to its inhabitants, and enough for them as a first lesson. The literature of science, however, of the present day, will tell them that long ages after the earth was evolved into a globe, it must have been in a molten, liquid state, surrounded by an atmosphere of vapours of some of the chemical elements so dense that no light from without could shine through it, and could only be penetrated by light after the cooling of the earth had dispelled a sufficient portion of that dense atmosphere. With this explanation, which they had at hand for the looking for, they might have been so far satisfied, and have left Moses to tell his story in his own way. In passing, it may not be out of place to say that, after the cooling of the earth had proceeded so far that the vapours of matter had been condensed and precipitated on its surface, all boiling of water whether in the seas or on its surface must soon have ceased, so that no inconceivably enormous volumes of steam could be thrown upwards to maintain an atmosphere impenetrable to light ; and that when dense volumes of steam ceased to be thrown up, the condensation of what was already in the atmosphere would be so rapid, and its density so soon reduced sufficiently to admit of the passage of light through it, that one can almost fancy himself present on the occasion and appreciate the sublimity of the language. "And God said, Let there be light, and there was light " ; more especially if he had ever stood by the side of the cylinder of a large steam engine, and understood what he heard when the steam rushed from it into the condenser, and noted how instantaneous it seemed to be. Any one who has watched a pot of water 8 New Theories in Astronomy. boiling on the fire and emitting clouds of steam, will have noticed how immediately the boiling ceased whenever the pot was removed from the fire ; but he will also have noticed that the water still continued to emit a considerable quantity of vapour, and will be able to understand how it was that the cloudy atmosphere of the earth, at the time we are dealing with, could allow light to pass through it but still keep the source of light from being visible. He experiences daily how thin a cloud will hide the sun from his sight. But there is more to be said about this when the time comes for taking note of the actual appearance on the scene of the sun, moon, and stars. To obtain some rude idea of the time to be disposed of for evolution during the first period, let it be supposed that the whole of the time consumed in the creation and develop- ment of the earth was 300 million years, as demanded by some geologists, the first period of the six would naturally be somewhere about 50 millions of years, a period which would allow, probably, very liberal time for evolution, but could never have been consumed in creation, seeing that creation has always been looked upon as an almost instan- taneous act. And if anyone is still capable of exacting that the period was a day of twenty-four hours, he has to acknow- ledge that at least twenty-three of them were dedicated to the work of evolution. The second period was evidently one solely of evolution, as all that was done during it was confined to making the firmament which divides the waters from the waters ; an operation which could never be confounded with creation, being probably brought about solely by the cooling of the earth, which was the only means by which a separation between the waters covering the earth, and those held in suspension above it by the atmosphere, could be brought about, and must have been purely the work of evolution. The third period was begun by collecting the waters under the firmament into one place and letting the dry land appear ; which, it may be well to note, gives it to be understood that the surface of the solid part of the earth had come to be Introduction. 9 uneven either by the elevation or depression, perhaps both, of some parts of it, and next the earth was let bring forth grass and trees, and in general vegetation of all kinds. These cannot be considered otherwise than as operations of evolu- tion : there was no creation going on beyond what may have been necessary to help evolution, and of that not a word is said. Here it is well to notice that until the waters were gathered together into one place and the dry land appeared there could be no alluvial deposits made in the sea, and that till well on into this third period, that is well on for 1 50 million years from the beginning, there could be no geological strata deposited in it containing vegetable matter, for the very good reason that although rains and rivers may have swept earthy matter into the sea, the rivers could not carry along in their flow any vegetable matter until it had time to grow. Should evolutionists think they have discovered something new in spontaneous generation, we refer them to the nth verse of the chapter, where they will see " And God said, Let the earth bring forth grass, the herb yielding seed, and the fruit-tree yielding fruit after his kind, whose seed is in itself, upon the earth." The conclusion of this passage asserts plainly that the seed was already in the earth, somehow or other, ready to germinate and sprout when the necessary accompanying conditions were prepared. The words are very few, and they can have no other meaning. In the first period " God made two great lights : the greater light to rule the day and the lesser light to rule the night. ; he made the stars also." This passage has been "a stumbling block and rock of offence" to some people possessed of much knowledge and to some possessed of little ; the one party professing to disbelieve all because the sun was made four days after there was light, and the other party, supposing that there might have been light proceeding from some other source during the first four days. Both parties seem to have forgotten that the earth was created without form and void, and that being so the same would naturally be the case with the sun and the moon ; all of them had to be made into form after their creation. By what means ? By evolution, of TO New Theories in Astronomy. course, or whatever else anyone chooses to call it ; that will make no difference. As far as it can penetrate into the mysteries of creation, Physical Astronomy has endeavoured to show how the solar system may have been formed out of a mass of nebulous matter. Furthermore, as has already been adduced in evidence, that at one time the earth must have been a molten, liquid globe surrounded by vapours of metals, metalloids, gases, and finally by water; and even goes the length of supposing that the planets were evolved to something approaching their present state, long before the sun attained its present form. Follow- ing up this hypothesis, it is more than probable that the sun had not attained that form when this fourth period began, and, although capable of emitting light early in the first period, still required a vast amount of evolution to reduce it to the brilliant globe now seen in the heavens. Everybody knows that plants grow without sunshine, and it is generally believed that the primary forests of the earth grew most rapidly in a moist, stifling atmosphere, which neither admitted of animal life, nor could be penetrated by sunshine. Thus Physical Astronomy cannot say that the sun could not have been made into its present state until near the end of this fourth period. It may have been as bright as it is now, though very probably not, as we shall see in due time ; but it could not shine upon the earth, neither could the earth, nor anything thereon, see it. It is not necessary to say anything about the moon, as it only reflects sunlight, and the reflection could not reach the earth if the light could not. In the fifth period the waters were let " bring forth the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven." Here again spontaneous generation may have been provided for before- hand, the same as in the case of vegetation. Also it is said " God created great whales," and it is to be observed that this is only the second time that creation has been mentioned in the book, and would seem to teach that making^ or evolution, was the most active agent at work in the construction of the earth and, we may add, of the universe. Introduction. 1 1 The sixth period was one almost exclusively of evolution, unless it should be considered that spontaneous generation is a different, and newly discovered process. In it God made the beast of the earth, cattle, and everything that creepeth upon the earth, after his kind. Last of all : " God said, let us make man in our image, after our likeness." Thus it appears that the only work of creation done in this period was that of creating man, and even that after some length of time and work had been expended in making or evolution, which may have extended over a very considerable portion of the fifty millions of years corresponding to it. We have supposed the work of creation to have extended over three hundred million years to satisfy some geologists, but our arguments would not be affected in any way by the time being reduced to the limit given by Lord Kelvin to the heat-giving power of the sun in the past, which he has made out to be between fifteen and twenty million years. That would only limit our periods of evolution to two and a half or three million years each ; each of them quite long enough to be totally inconsistent with our ideas of creation, which conceive of this as an instantaneous act. But although Lord Kelvin has in rather strong terms placed this limit, he at the same time says that it could by no means exceed four hundred million years, which is one-third more than we have calculated upon. Neither can our arguments be affected in any serious way by our dividing the periods into fifty million years each ; these may have varied much in length, but whatever was taken from one would have to be added to the others. Furthermore, we may be allowed to say that fifteen to twenty millions of years of the sun's heat at the rate it is now being expended, can be no reliable measure of the time re- quired for the operations of geology, for the reason that its heat must have been emitted in proportion to the quantity it possessed at any time. When it was created without form and void as no doubt it was, the same as the earth, it would have no heat to emit, but that does not mean that it possessed no heat until it was formed into the brilliant globe that we cannot now bear to turn our eyes upon. Even when it became 1 2 New Theories in Astronomy. hot enough to show light sufficient to penetrate the " darkness that was upon the face of the deep," it may still have been an almost shapeless mass, and have continued more or less so until it was formed into the body of the fourth period, which may even then have been very different from what it is now. Thus geology would have not far from one hundred and fifty million years in which a very small fractional part of the sun's emission of heat would suffice for its operations. But we shall have more to say on this subject when the time comes. It being, therefore, a matter beyond all question to people possessed of the faculty of thinking, and of candour to confess that they cannot help seeing what has been set plainly before their sight and understanding that the opening chapter of the book of Genesis plainly teaches that making evolution had a very large and active part to perform in the creation of the universe and much more within our grasp of the earth ; we can come to the conclusion that the theory of evolution, instead of being new and wonderful, comes to be almost in- finitely older than the everlasting hills, without losing any of its power of inspiring inexpressible wonder. Looking back over the examination into the first chapter of the book of Genesis we have just concluded, we cannot conceive how it could ever have entered into the thoughts of man, that the state of vegetable and animal life on the earth, at the present day, must have been brought about by continual and unceasing acts of creation, when creation has been men- tioned only on three occasions during the whole process described in the chapter we have analysed, that is, 3 out of 31 verses ; and while the other processes which we have brought forward making and spontaneous generation have never been alluded to, perhaps not even thought of. We have no desire, neither are we qualified, to follow up this subject any further, but we have still one or two things to bring into remembrance. One of the most illustrious of the founders of the Theory of Evolution has based his dissertations on the Descent of Man, on the Variation of Animals and Plants under Domestic- ation, and on their wonderful plasticity under the care of man. Introduction. 1 3 Here there is an explicit acknowledgment of the necessity for the direction of an intelligent guiding power to produce such variations ; these never having any useful or progres- sive results except under such care. If, then, there is a necessity of such directing and guiding power in the case of variations of such inferior importance, the superintendence of some similar power must have assuredly been much more necessary for the creation and evolution of matter, of life, and of man himself. This is what, one would think, common sense and reason would point, and what the Theory of Evolu- tion seems to think evidently without studying the subject far enough ; but all that it has been able to do has been to substitute Nature for the Creator to whom Moses has ascribed not only Creation but the Making Evolution of the uni- verse. This naturally leads us to speculate on what Evolutionists consider Nature to be, and as none of them nor anyone else as far as we know, has ever thought it necessary to define Nature, we have to endeavour to draw from their writings what, in some measure and some way, they would like us to believe it to be. We find, then, that the base of their opera- tions seems to be Natural Selection, which can hardly be interpreted in any other way than by calling it the Selection of Nature. Thus, then, they apparently want us to look upon Nature as the First Cause. But, if Nature can select, it must be a being, an entity, a something, that can distinguish one particle of matter from another, and be able to choose such pieces of it, be they protyle or protoplasm, and to make them unite, so as to form some special body, organic or inorganic. It is plain, also, that Selection can only be performed by such a being, or something, such as just so far described, that can distinguish, choose, and arrange the particles of matter des- tined to form the very smallest body or the universe. Thus we see that in whatever way the basis of the Theory of Evolution is looked upon even for its own evolution there is required a being of some kind that has knowledge and power to evolve or make all things that are "in heaven above, or in the earth beneath, or in the waters under the earth." So we 14 New Theories in Astronomy. see that, if the theory of evolution dethrones the Creator and Evolver of the first chapter of Genesis, it has to enthrone another god which it calls Nature ; and has to get rid of that god, and any number of others, before it can be what it pretends to be. We are all very voluble in talking of Nature, and en- thusiastic in admiring its beauties, wonders, and wisdom, but it seldom occurs to us that we are really doing so without thinking of whence come the beauty, wonders, and wisdom. We must, therefore, not be too hard on evolutionists, as they have only done what we all do every day of our lives ; but if the theory of evolution is to be looked upon as a branch of science, we would recommend its students to open their eyes and think of it as a process which has been in existence from the beginning of things at least, and not as one of their inven- tion or discovery. They may be able some day, through more accurate study and more convincing argumentation than they generally use, to lay claim to having discovered, as far as it is possible for man to do, the modus operandi of evolu- tion, but that is all, and we would also warn some of them to think that, when we see them in their highest flights of science, genius, and self-sufficiency, we can " Conceive the bard the hero of the story." We have read a good deal of what has been called the War of Science, without having been able to see that there ever was any cause for such a war, with the exception of ignorance. If Theology had been able, or rather had taken the trouble, to study thoroughly the first chapter of Genesis, and thus to comprehend that, if the earth was created without form and void, a great deal of work had to be done, after creation, in forming it into its present condition, there was no call upon it to find fault with Copernicus or persecute Galileus, because they said the earth revolved round the sun ; more especially as they do not appear to have ever said anything against religion or revelation. Neither was there any necessity for opposing the so-called new science of evolution, because it Introduction. 1 5 (Theology) ought to have seen that the work expended in reducing the earth into form could hardly be conceived of otherwise than as a process of evolution; and would thus have been in a position to tell the authors of the new science that they had only discovered what had existed before the beginning of time. On the other hand, there was no occasion for Science to take up the war. If it, in its turn, had taken the trouble to study and understand the first chapter of Genesis, it could have shown Theology that it did not comprehend, and could not give a true account of what religion and revelation are ; whereas it (Science) seems to have had a strong tendency to demonstrate that religion and revelation are altogether false, and that the great work it has to perform is to dethrone Theology, and set itself up it in its stead. It is not worth while even to think of who or which was the aggressor, seeing that the war originated from ignorance caused by want of thought and study on both sides. All that has to be said on the subject reduces itself to the fact that both Religion and Science have been coming, and are at present going, through the process of evolution. Can anyone say that Science has been truly scientific, without ever incurring in error, from the beginning of history up to the present day ? Will any one venture to maintain that there has been no evolution, no progress, no softening of the spirit of Religion, from the institution of Christianity up to the end of the nine- teenth century ? If such there be, let the one look back to the time of Aristotle, and the other to the establishment of the Church under Constantine. There has been for long an opinion, which goes on increas- ing in strength, that Science will ultimately reform Theology and put Religion in its right place ; but if such is to be the case, Science has to begin by reforming itself and putting an end to error it has been, in many cases, teaching for genera- tions ; and by ceasing to formulate new theories, or bases of progress, which can be in many cases exploded by suppressing some of the error just alluded to. Little advance is made in science by forming hypotheses and theories, however brilliant 1 6 New Theories in Astronomy. they may appear, unless they are carefully studied and thought out to the very uttermost ; because, if published abroad on the authority of some celebrated or even well- known name, they have a tendency to stop further investiga- tion, and prevent students from exercising their own judgment and perhaps discovering what they might possibly find out were they to study them to the very end for their own satis- faction. This is in some measure the case even with respect to the solar system. We believe it can be shown that a more complete knowledge and comprehension of it, and even of the universe, has been kept back by the unquestioning acceptation by successive astronomers of the ideas and conceptions of their predecessors. We have to acknowledge, at the same time, that Astronomy could not start into perfection at once, any more than any other science, and it is not to be wondered at that in times past ideas relating to it should have been formed without being properly thought out ; even ideas that could not be properly thought out to the end for want of the requisite knowledge. But it is much to be regretted that such ideas should continue to be published at the present day as trust- worthy instruction for readers who may look upon it as strictly correct. Among those who read text-books even on Astro- nomy, there must be a very considerable number who are rather surprised when they see statements made which do not agree with what they were taught at school, or with what they have practised in other sciences in their own professions or trades. It may be said that any person of ordinary intelligence will easily be able to correct such errors, but the evil does not stop here. If he can really correct them he will most probably find as well, that his instructors have been led into more serious errors, perhaps in more important matters, founded on the ideas which they had not fully studied out before giving them a place in their books. He may also find sometimes, in his reading, such ideas brought forward to substantiate some theory, just as far as they are required and then dropped, while a step or two further forward in the examination of these same ideas, would have exploded the theory altogether ; Introduction. 1 7 because, although founded to a certain extent on one law of nature, they are in contradiction with what is laid down in some other law. The above will be looked upon as an unwarrantably bold assertion ; but a careful study of, or attention to, what is taught in the most advanced works on the solar system, even in science generally, will show it to be perfectly true. It is not only true, but the consequences of its being true have been much more serious than will be readily believed. In our own endeavours to understand what we had been reading, we have seen that some of the notions presented to us were only half formed, and that they have led to theories being founded which could never have been entertained at all had they been thoroughly studied out. More than that, they have prevented the truth from being arrived at in the fundamental conceptions of the construction of the earth, and, as a natural consequence, of the whole solar system, perhaps even of the whole universe. There are probably many, even a great many, people who have arrived at the same conclusions as we have, but as far as it has been in our power to search into the matter, we have met with no attempt from any quarter to put an end to this defect in the literature of science ; perhaps because the work has the appearance of being too great to be readily undertaken, and also because it may be thought that there is little to be gained by it as all is sure to be set right through time. But, as we believe that it will be beneficial immediately, in the case of the earth and solar system at least, we shall first attempt to show what are some of the defects alluded to, and then what knowledge may be acquired through their removal. 1 8 New Theories in Astronomy. '. rY ) , CHAPTER I. PAGE 18 The bases of modern astronomy. Their late formation. 19 Instruments and measures used by ancient astronomers. 20 Weights and measures sought out by modern astronomers. 20 Means employed to discover the density of the earth. Measuring by means of plummets not sufficiently exact. 21 Measurements with torsion and chemical balances more accurate. 22 Sir George B. Airy's theory, and experiments at the Harton colliery. 23 Results of experiments not reliable. Theory contrary to the Law of Attraction. 24 Proof by arithmetical calculation of its error. 26 Difficulties in comparing beats of pendulums at top and bottom of a mine. 27 The theory upheld by text-books without proper examination. 28 Of a particle of matter within the shell of a hollow sphere. Not exempt from the law of Attraction. 29 A particle so situated confronted with the law of the inverse square of distance from an attracting body. Remarks thereon. 31 It is not true that the attraction of a spherical shell is "zero" for a particle of matter within it. BEFORE astronomers could begin to determine the relative distances from each other, and the relative dimensions and masses of the various members of the solar system, they had to establish scales of measurements appropriate to their under- taking. This entailed upon them, of course, the necessity of determining the form, the different circumferences and dia- meters, and the weight of the whole earth, as any other scales derived from the only available source, the earth, would have been too small to give even an approximate value of the measures and masses to be sought for. History tells us that at least one attempt had been made, over two thousand years ago, to find the- circumference and necessarily the diameter of the earth, but it says nothing of any to ascertain its weight. There may have been many to determine both diameter and mass, but we know nothing of them ; and when we think seriously about this, we cannot help New Theories in Astronomy. 19 feeling somewhat surprised that no attempt had been made to find out the density and mass till more than a century after Sir Isaac Newton's discovery of the law of Attraction, or Gravitation, as it is more usually called. But perhaps this is an idea that could only occur to one who has been spoilt by witnessing, in great measure, the immense strides in advance that have been made during the nineteenth century in science of all kinds, and does not duly take into account the immense labour, and the incessant meeting with almost insurmountable difficulties, that astronomers have had to encounter and over- come between the birth of modern astronomy and the end of the eighteenth century. Indeed, the difficulties can hardly be looked upon as altogether overcome even yet, as efforts are still being made to find out the exact distance of the sun, and it is not impossible that some small difference may be found, plus or minus, in the density at present adopted for the earth of 5 '66 times the weight of water. The geometer who, more than two thousand years ago, set himself the task of measuring the circumference of the earth, is supposed to have made use of very much the same kind of implements as those employed by modern astronomers. He must have had a very fair instrument for measuring angles, and have known very well how to use it, seeing he was able to determine a value for the obliquity of the ecliptic which agrees so well with that established by modern science, its variations being, for what we know, taken into account ; and for length or distance he would doubtless have some implement analogous to the metre, chain, foot-rule, or something called by other name that would, in those days, present facilities for selling a yard of calico. His operations would probably be as plain and simple as those applied to the measuring of a village green for we are not told that he had any idea of there being any difference between the length of a degree of the meridian at the equator and one nearer either of the poles and in- volved no hypotheses or theories, any more than modern operations have done. When the time came for making efforts to ascertain the density of the earth, science seems to have employed the very C 2 2O New Theories in Astronomy. simplest means it had at its disposal for attaining its object, and to have gone on refining its implements and operations in conformity with the lessons it went on learning while pursuing its self-imposed task. Every one who, even for recreation, has read a fair amount of the multitude of works and writings that have been published on Popular Astronomy not to speak of text-books knows that the first attempts were made by measuring the attraction of steep, or precipitous, mountains for plummets suspended in appropriate positions in their neighbourhood ; then evidently from knowledge acquired during these operations by the attraction for each other of large and small leaden balls suspended on frames and torsion balances, which go under the name of the Cavendish Experiment ; and afterwards by a refinement on this in using the Chemical Balance, where only one large and one small ball of metal are required. All these operations and their results are to be found described in works of various kinds, and are generally reduced to something like the following tubular form, which we reproduce in order to make more intelligible what we have just said, and that we may make a few remarks upon them. There is no hypothesis, no theory, connected with any of the operations, unless it was the supposition that a plummet which was naturally believed to point to the centre of the earth should be pulled to one side by the attraction for it of a mountain in its neighbourhood, and that was found to be a fact. METHODS EMPLOYED FOR FINDING THE DENSITY OF THE EARTH, AND THEIR RESULTS. (1) Deviation of Plummet by the Attraction of Mountains : Experiments made. By whom, and Date. Mean Density found. At Schiehallien . . Maskelyne . 1772 . . 4*713 At Arthur's Seat . . Sir H. James . 1855 . . 5-316 (2) Torsion Balance Experiments : Cavendish . 1798 . . 5*448 At Freyberg, Saxony . Reich . . 1837 . . 5^438 At Manchester . . Francis Baily 1838-1842 . 5^675 (3) Chemical Balance Experiments : J. H. Pointing 1878 . . 5-690 New Theories in Astronomy. 21 In the case of the plummet deviating from its absolutely straight direction towards the centre of the earth, caused by their attraction, not only the mountains themselves had to be measured and virtually weighed as far as they were measurable, but the weight of the wedge or pyramid between that measur- able point, in each case, and the centre of the earth had to be estimated in some way ; then the centre of gravity of the whole of this mass had to be ascertained, as well as the respec- tive distances from the centre of the earth of this centre of gravity and that of the plummet, and only after all this and a deep study of the mutual attractions of this mass and the plummet could an estimate be formed of the mass of the earth. It will thus be seen that such measurements and estimates could never be looked upon as very exact and reliable ; and nevertheless they have come very near the density of 5 66 finally adopted for the earth. In the case of the Torsion Balance experiments a very considerable advance was made in consequence, most un- doubtedly, of the knowledge acquired from what had been done by Maskelyne. When it was found that the attraction of Schiehallien for the plummets was such a measurable quantity, Cavendish evidently saw that the attraction of manageable leaden balls for each other would be measurable also, and that as no calculations of any kind whatever were necessary to find the masses of the balls, the mutual attraction of large and small balls would furnish a more exact means of measuring the density of the earth, than the roundabout way of having to calculate the weight of a mountain as a beginning ; and with the requisite ingenuity, invention, and labour, he found the means of applying the torsion balance, to make the experiments. After these experiments were revised by Reich and Baily and the density of 5 '66 adopted, we believe still another set were undertaken by J. H. Pointing, with the Chemical Balance, in which only two metal balls, one large and one small were required, which gave a density of 5 "690 as shown opposite, and from its extreme simplicity may perhaps have been the most exact of all. 22 New Theories in Astronomy. We have said, we think with truth, that there is no hypo- thesis or theory involved in any of these experiments, but only the simplest form of we might almost say arithmetical cal- culation. But there is a theory built up on hypothesis which has no foundation whatever, and about which most people, who take the trouble to study it out to the very end, will come to the conclusion that " the less said the better." This, at all events, is our opinion, and we would not have taken any notice whatever of it had it not been that up to the present day, it is published in many works on Popular Astronomy, and even in some text-books, and is looked upon in them, apparently, as an example of the transcendent height to which human science can reach. We allude, of course, to the theory that the deeper we go down into the earth at least to an undefined and undefinable depth the greater is its attraction for the bob of a pendulum at that depth, and the greater the number of vibrations the pendulum is caused to make in a given time. The explanation of the theory is, that were the earth homogeneous throughout its whole volume, the pendulum ought to make the fewer vibrations, the deeper down in the earth it is placed ; but as the earth is not homogeneous, it actually makes a greater number of vibrations in a given time, because the attractive force of the earth increases up to the undefined and undefin- able depth on account of the denser matter beneath the pendulum bob more than overbalancing the loss of attraction from the lighter matter left above it. The author of the theory was the late Astronomer Royal, Sir George B. Airy, who from it endeavoured to calculate the mean density of the earth, and with that view made two experiments which are thus described by Professor C. Piazzi Smythe in his work on the Great Pyramid : "Another species of experiment . . . was tried in 1826 by Mr. (now Sir) George B. Airy, Astronomer Royal, Dr. Whewell, and the Rev. Richard Sheepshanks, by means of pendulum observations at the top and bottom of a deep mine in Cornwall ; but the proceedings at that time failed. Subsequently, in 1855, the case was taken up again by Sir New Theories in Astronomy. 23 George B. Airy and his Greenwich assistants, in a mine near Newcastle. They were reinforced by the new invention of sympathetic electric control between clocks at the top and bottom of a mine, and had much better, though still unex- pectedly large results the mean density of the earth coming out, for them, 6*565." From other sources we have also found that the pit, or mine, was at the Harton Colliery and 1260 feet deep, that the pendulum at the bottom of it gained 2\ seconds on the simi- lar one at the top, in 24 hours ; and that the surrounding country had to be extensively surveyed, the strata had to be studied, and their specific gravities ascertained. A little unbiassed thought bestowed on this theory will at once show that it begins by violating the law of attraction discovered by Newton, when he showed that the mutually attractive forces of several bodies are the same as if they were resident in the centres of gravity of the bodies. In the case in point this means, that the attraction of the earth for the bob of the pendulum at the top of the mine was the same as if all its force was collected at its (the earth's) centre. In that posi- tion the force of the earth's attraction comprehended, most un- deniably, the whole of its attractive power, including whatever might be imagined to be derived from the non-homogeneity of the earth, due to its density increasing towards the centre ; and we are called upon to believe that when, virtually, the same pendulum was removed to the bottom of the mine, and a segment 1260 feet thick, at the centre as good as cut off from the earth and as far as the pendulum was concerned hung up on a peg in a laboratory, the diminished quantity of its matter had a greater attractive force, a very little beyond the centre non-homogeneity again included than the whole when the sphere was intact. This we cannot do, because all that we can see in the placing of the pendulum at the bottom of the mine, is that the position of the bob has divided the earth into two sections, one of which has a ten- dency to pull it up towards the surface, and the other to pull it down towards its centre of gravity ; and because the mass of the smaller segment is so insignificant that its entire removal to 24 New Theories in Astronomy. the laboratory peg, not only could not produce the reverse action, on which the theory is based, but could not be measured by any stretch of human invention or ingenuity ; it is far beyond the reach of mathematics and human comprehension of quantity. The difficulty of belief is increased when we reflect that, were the pendulum taken down towards the centre of the earth, the number of its vibrations in a given time ought gradually to decrease as it approached the centre, and would cease altogether when that point was reached. And we feel confident that no mathematician could calculate where the theoretical acceleration of the vibrations would cease, and the inevitable retardation commence ; where the theory would come to an end and the law of attraction begin to assert its rights, simply because he does not know how the non- homogeneity is distributed in the earth. No man can tell, even yet, how the mean density of 5*66 is made up through- out the earth, and without that any theory founded on its non-homogeneity is out of place. But to follow up our assertion of non-commensurability- Taking the diameter of the earth at 8000 miles, and its mean specific gravity at 5*66, its mass would be represented by 1,517,391,000,000 cubic miles of water. On the other hand > supposing the earth to be a true sphere, the volume of a segment of it cut off from one side, at one quarter of a mile deep not 1260, but 1320 feet would be 785*35 cubic miles in volume, and if we suppose its specific gravity to be 2 5 greater most probably than the average of all the strata in the neighbourhood of the Harton Colliery its mass would be represented by 1963*38 cubic miles of water. Then, if we divide the mass of the section below the pendulum, that is, 1,517,391.000,000 minus the mass of the one above it, 1963-38, viz. 1,517,390,998,036-62 by the mass of 1963-38 just men- tioned, we find that the proportion they bear to each other is as I to 772,846.315. This being so, we are asked to believe that by removing 772 s \ 6 315 tn P art f tne mass f ^ e eartn from one side of it, its force of attraction at the centre will not only not be decreased, but will be so increased that it will New Theories in Astronomy. 25 cause a pendulum, suspended at the centre of the flat left by the removal of the segment, to vibrate 86,402 '25 times in twenty-four hours instead of 86,400 times as it did when sus- pended at the surface before the segment was removed ; that is, that the vibrations will be increased by 38 400^ P art * Again we cannot do so. Had we been asked to believe that the removal of so small a fraction as decreased the earth's attraction at its centre, so much as to produce a diminution of 38 4 00 tn P art m tne number of vibra- tions of the pendulum, we could not have done so ; how much less then can we believe that the central attractive force had increased so much as to produce an augmentation of the vibrations in the same proportions ? But more in this strain presently. We have no doubt whatever that Sir George B. Airy and his assistants satisfied themselves that the pendulum at the bottom of the mine gained 2j seconds in twenty-four hours over the one at the top, but they may have been deceived by their over-enthusiastic adoption of what seemed to be a very grandly scientific theory, or by some unperceived changes in the temperature in the pendulums, caused by varying ventila- tion in the mine or the varying weather outside of it, or by the insidious manifestations of the " sympathetic electric control between clocks at the top and bottom of a mine," called in to assist at the experiments. An error of 38 1 40() th part of the time the sympathetic electricity would take to travel from the top to the bottom of the shaft would be sufficient to make the experiments of no value whatever ; not to speak of the small errors that may have been made in surveying the surrounding country, calculating the specific gravities of the strata for we are told that all this had to be done and applying the elements thus obtained to the solution of the problem they had in hand. We have read of the difficulties met with by Mr. Francis Baily when he began to revise the Cavendish Experiment some twelve or fifteen years before the final Harton Colliery experiments were made, and suppose it possible that they met with similar difficulties without being aware of it. And 38.400^ P art ' 1S suc ^ a ver y sma ^ fractional difference in the 26 New Theories in Astronomy. vibrations in twenty-four hours, of the pendulums of the two separate clocks, that taking into consideration the circum- stances under which it was found it would hardly be looked upon as reliable at the present day, when the clocks of astronomical observatories are placed in the deepest cellars or even caves available, so as to free them as much as possible from variations of temperature. Having referred to the difficulties met with by Mr. Baily, we believe it worth while to transcribe Professor C. Piazzi Smythe's account of them, given in his work already referred to at page 22 ; because it not only has a very direct bearing on what we have been saying of changes of temperature, but is exceedingly interesting, and probably very rarely to be met with in other works. It is as follows : " Nearly forty years after Cavendish's great work, his experiment was repeated by Professor Reich of Freyberg, in Saxony, with a result of 5*44; and then came the grander repetition of the late Mr. Francis Baily, representing therein the Royal Astronomical Society, and, in fact, the British Government and the British Nation. " With exquisite care did that well-versed and methodical observer proceed to his task, and yet his observations did not prosper. " Week after week, and month after month, unceasing measures were recorded ; but only to show that some dis- turbing element was at work, overpowering the attraction of the larger on the smaller balls. " What could it be ? " Professor Reich was applied to, and requested to state how he had continued to get the much greater degree of accordance with each other, that his published observations showed. " ' Ah ! ' he explained, ' he had to reject all his earlier observations until he had guarded against variations of temperature by putting the whole apparatus into a cellar, and only looking at it with a telescope through a small hole in the door.' "Then it was remembered that a very similar plan had New Theories in Astronomy. 27 been adopted by Cavendish, who had furthermore left this note behind him for his successor's attention 'that even still or after all the precautions which he did take, minute varia- tions and small changes of temperature between the large and small balls were the chief obstacles to full accuracy.' " Mr. Baily therefore adopted yet further, and very pecu- liar, means to prevent sudden changes of temperature in his observing room, and then only did the anomalies vanish and the real observations begin. " The full history of them, and all the particulars of every numerical entry, and the whole of the steps of calculation, are to be found in the Memoirs of the Royal Astronomical Society, and constitute one of the most interesting volumes (the Four- teenth) of that important series ; and its final result for the earth's mean density was announced as 5*675, probable error 0-0038." After reading this story of Baily's experiments with care, one cannot help feeling something stronger than want of confidence in those made at the Harton Colliery, especially after what has been shown of the smallness of the fraction of the earth that was dealt with, and due consideration is given to the insignificant difference of effect that the non-homogeneity of the earth could produce on the remainder after the sup- posed removal of such a small fraction ; and here we might let the theory drop. Perhaps it may be thought that now there is nothing to be gained by spending time and work in showing it to be more truly erroneous than we have yet made it out to be ; but if there is error, it cannot be too clearly exposed, and the sooner it is put an end to, the better ; more especially as it has been accepted as true by some authors of text-books, and by some competent astronomers who, in trying to explain the anomaly of the increase instead of decrease in the force of attraction at the bottom of a mine compared with the top, have used arguments which are not consistent with the law of gravitation, or rather attraction. Messrs. Newcomb and Holden in their work, entitled " Astronomy for High Schools and Colleges," sixth edition, 1889, apparently accept the theory, and proceed to explain 28 New Theories in Astronomy. and support it by showing what would be the action of a hollow spherical shell of any substance on a particle of it, say the bob of a pendulum, placed on the outside and also on the inside of the shell ; and give us two theorems which are supposed to comprehend both cases. These are : (1) "If the particle be outside of the shell, it will be attracted as if the whole mass of the shell were concentrated at its centre." (2) "If it be inside the shell, the opposite attractions in every direction will neutralise each other, no matter where- abouts in the interior the particles may be, and the resultant attraction of the shell will therefore be zero." To the first theorem no objection can be made : The particle on the outside of the shell will undoubtedly be at- tracted by every particle in the shell, with the same force as if the attractive power of all the particles composing it were concentrated in the centre. Not so with the second theorem : for it can be objected that it altogether ignores the Law of Attraction laid down by Sir Isaac Newton, where it asserts that the resultant attraction of the shell for the particle will be zero, when it is placed anywhere on the inside. In fact the theorem supposes a case impossible for the Harton Col- liery experiments, in order to demonstrate their accuracy ; for it makes use of the bob 6f the pendulum a particle of matter as if it were transferable to any part of the interior of the earth instead of being confined within the bounds of its swing. That the attraction of the shell 1260 feet thick all round the earth on the pendulum bob inside of it continues in all its force, and is only divided into two opposing parts, is made plain by Fig. I. Supposing O to represent the bob of the pendulum at the bottom of the mine, and the space be- tween the two circles the shell of the earth. Then the line B C will show where the attraction of the shell for the bob is divided into two parts acting in opposite directions. Suppos- ing these two parts to be separated from each other, only far enough to admit the bob a particle to all intents and pur- poses between them ; the part BAG will attract the bob as if its whole attractive force were collected at its centre of New Theories in Astronomy. 29 gravity, and the part B D C as if the whole of its attractive force were collected, not at the centre B of the shell, but at its centre of gravity, a very little distance from B in the direc- tion towards D. This is an incontrovertible fact, because it is in strict accordance with Newton's Law of Attraction, which is : Every particle of matter in the universe attracts every other particle with a force directly as their masses, and inversely as the square of the distance which separates them. If we now suppose the interior of the shell to be filled up solid, that will make no difference, because the mass of the part B D C will only be increased vastly thereby, while the mass of A B C will remain the same ; the two parts only increasing their proportion to each other, and thus coming to be for the earth in the Harton Colliery experiments what we represented them to be at page 24 ; and we can now proceed to find the attractive force of each of the two masses for the bob of the pendulum which is as the inverse square of their distances from it. These distances may be taken, with- out any very great stretch of conscience, as one-tenth of a 30 New Theories in Astronomy. mile and 3999*75 miles; because the centre of gravity of the segment ABC will be about that distance from O, and that of B D C cannot be adequately represented by a greater sum than 3999- 7 5, always supposing the diameter of the earth to be 8000 miles. Thus the squares of these two distances will be 0*01 and 15,898,000 miles respectively, and the relative force of attraction for the pendulum of the two segments ABC and BDC will be as I x O'Oi and 772,846,315, and 772,846,315 x 15,898,000; that is as I is to 1,228,671,000,000,000,000. Here then we get confirmed the unbelief in the theory we expressed at pages 23 and 24. Surely no one will be bold enough to assert that by decreasing the total attractive force of the earth by a little less than a \\ trillionth part cut off from one side of it, the want of homogeneity in what remains will not only not decrease its attractive force at the centre, but increase it so as to make a pendulum be lessened by 38 4 OQ th part of its time in beating one second. This fraction of time is quite small enough to inspire doubt of any theory founded upon it ; and if there ever is a quantity in mathematics that can be called negligible, the fraction of attractive force found above ought to be included in the same category. We may therefore assert that no human measurements could find a true difference between the beats of a seconds pendulum at the top and bottom of the pit at the Harton Colliery. If all the people who have puzzled themselves with this theory had spent an hour or two in making the above calculations before they began them, there would have been no experiments made, and the theory would have died almost ere it was born. Those who believed in it may have looked upon a particle as a negligible quantity, but as the whole earth is made up of particles a little thought would have put an end to such a notion. What puzzles us is how such a theory could be formed by people who knew nothing whatever of the nature of the interior of the earth at a depth of even one mile, and how they could speculate on its want of homogeneity without knowing anything of how the density of 5 66 is made up in it ? To suppose that the earth is made up of strata of different densities, and that each New Theories in Astronomy. 31 is in some degree elliptical the ellipticity of one stratum being different from another, as the French mathematician Clairaut did is all very allowable ; but to build up any theory on any such suppositions is to build upon shifting sands without examining the foundations. For anything that is known up to the present time, the density of the earth may go on increasing gradually from the surface to the centre, or it may attain nearly its greatest density at a few miles from the surface, and continue homogeneous or nearly so from there to the centre. To go further now : it is not true that the attraction of a hollow shell of a sphere for any particle within it, is the same " no matter whereabouts in the interior the particle may be." The only place where the attraction will be the same is when the particle is at the centre. In that position a particle would be in a state of very unstable equilibrium, and a little greater thickness of the shell on one side than the others, would pull it a little, perhaps a great, distance from the centre towards that side ; and if we extend our ideas to a plurality of par- ticles within the shell of a sphere, we are led to speculate on how they would be distributed, and to see the possibility of there not being any at all at the centre. This is a point which has never been mooted, as far as we have been able to learn, and we shall have to return to it when the proper time comes. It is difficult to understand how any man could conceive the notion that a shell of a sphere, such as that shown at Fig. i, could have no attraction for each separate one of all the particles which make up the mass of the whole solid sphere within it ; for that is the truth of the matter if properly looked into, when it is asserted, as has been done by Messrs. New- comb and Holden, that " the resultant attraction of the shell will therefore be zero." If such a notion could be carried out in a supposed formation of the earth, an infinity of particles would carry off the whole of the interior, and leave the earth as only a shell of 1260 feet thick, as per the Hartley Colliery experiment ; only we are told, or left to understand, that that process could not go on for ever, but would have to come to an end somehow and somewhere ; and then we are left to 3^ New Theories in Astronomy. speculate on how the unattracted particles could come back to take part in the composition of the earth. Left to our- selves we can only liken the process to that followed by a man who peels off the outer layer of an onion, eats the interior part, and when he is satisfied throws down the outer layer and thinks no more of it ; not even that he might be asked what had become of the interior part. Curiously enough, there is a way of explaining how, or rather why, the notion was formed not unlike the one just given to be found in the third of Sir George B. Airy's lectures on Popular Astronomy, delivered at Ipswich several years before the final experiments were made at the Harton Colliery. In that lecture, while describing how the Greek Astronomers accounted for the motions of the sun and planets round the stationary earth, he says, " It does appear strange that any reasonable man could entertain such a theory as this. It is, however, certain that they did entertain such a notion ; and there is one thing which seems to me to give something of a clue to it. In speaking today and yesterday of the faults of education, I said that we take things for granted without evidence ; mankind in general adopts things instilled into them in early youth as truths, without sufficient examination ; and I now add that philosophers are much influenced by the common belief of the common people." We can agree with Sir George B. Airy in his ideas about education, and now conclude by saying that he has given us a very clear and notable example of a theory being accepted very generally, without being thoroughly examined to the very end, and of how easy it is for such theories to be handed down to future generations for their admiration. New Theories in Astronomy. 33 CHAPTER II. PAGE 33 The moon cannot have even an imaginary rotation on its axis, but is generally believed to have. Quotations to prove this. 35 Proofs that there can be no rotation. The most confused assertion that there is rotation shown to be without foundations. 37 A gin horse does not rotate on its axis in its revolution. 38 A gin horse, or a substitute, driven instead of being a driver. 38 Results of the wooden horse being driven by the mill. 39 The same results produced by the revolution of the moon. Centri- fugal force sufficient to drive air and water away from our side of the moon. 40 That force not sufficient to drive them away from its other side. 41 No one seems ever to have thought of centrifugal force in connection with air and water on the moon. 41 Near approach made by Hansen to this notion. 42 Far-fetched reasons given for the non-appearance of air and water. 44 The moon must have both on the far-off hemisphere. 44 Proofs of this deduced from its appearance at change. 45 Where the evidences of this may be seen if looked for at the right place. The centrifugal force shown to be insufficient to drive off even air, and less water, altogether from the moon. 47 The moon must have rotated on its axis at one period of its existence. 48 The want of polar compression no proof to the contrary. 48 Want of proper study gives rise to extravagant conceptions, jumping at conclusions, and formation of " curious theories." A GOOD deal of theorising has been expended in accounting for the absence of all but traces of an atmosphere and water on the moon, which might have been avoided had astronomers not caught up the notion, and stuck to it, that it rotates on its axis once for every revolution that it makes round the earth. It might be difficult to find out with whom the notion originated ; but perhaps it was first conceived to be the case by some celebrated astronomer, and has been accepted by almost all his successors without being properly looked into. Any one who chose to take the trouble to study the matter thoroughly, would have easily discovered that the moon can have no rotation of any kind on its axis, and immediately afterwards have found out the reason why nothing beyond D 34 New Theories in Astronomy. traces of air and water were to be seen on the side of it constantly turned towards the earth. This is another example we can give of erroneous ideas leading to erroneous and impossible conclusions, and preventing the truth from being discovered. That the rotation of the moon on its axis is stated to be a fact, by recognised and celebrated astronomers, will be seen from the following quotations. (1) Sir John Herschel, in his "Treatise on Astronomy," new edition of 1835, says at page 230: "The lunar summer and winter arise, in fact, from the rotation of the moon on its own axis, the period of which rotation is exactly equal to its sidereal revolution about the earth, and is performed in a plane i 31' n" inclined to the ecliptic, and therefore nearly coincident with her own orbit. This is the cause why we always see the same face of the moon, and have no knowledge of the other side." (2) In his "Poetry of Astronomy," page 187, Mr. Proctor says : " For my own part, though I cannot doubt that the substance of the moon once formed a ring around the earth, I think there is good reason for believing that when the earth's vaporous mass, receding, left the moon's mass behind, this mass must have been already gathered up into a single vaporous globe. My chief reason for thinking this is, that I cannot on any other supposition find a sufficient explanation of one of the most singular characteristics of our satellite her revolution on her axis in the same mean time, exactly, as she circuits around the earth." (3) Professor Newcomb, in his " Popular Astronomy," 5th edition, 1884, at page 313, has what follows: "The most remarkable feature in the motion of the moon is, that she makes one revolution on her axis in the same time that she revolves around the earth, and so always presents the same face to us. In consequence, the other side of the moon must remain for ever invisible to human eyes. The reason for this peculiarity is to be found in the ellipticity of her globe." Then he enlarges upon and confirms the fact of her rotation. (4) Mr. George F. Chambers, in his " Handbook of As- tronomy," 4th edition, 1889, says at page 119, Vol. I.: "In New Theories in Astronomy. 35 order that the same hemisphere should be continually turned towards us, it would be necessary not only that the time of the moon's rotation on its axis should be precisely equal to the time of the revolution in its orbit, but that the angular velocity in its orbit should, in every part of its course, exactly equal its angular velocity on its axis." It may be necessary, to avoid misconception, to note that angular velocity on its axis confirms rotation ; and what is more extraordinary, that Chambers must have thought that its angular velocity on its axis must have increased and diminished in order to agree with its increased and diminished velocities in its elliptic orbit at its perigee, apogee, and quadra- tures. A rather strange notion in mechanics where there is no provision made for acceleration or retardation of rotation. (5) Dr. Samuel Kinns, in " Moses and Geology," twelfth thousand, 1889, says at page 208, "the same side of its (the moon's) sphere is always towards us. This could only happen by its having an axial rotation equal in period to its orbital revolution, which is 27 d. 7 h. 43 m. 1 1 s. (6) In the "Story of the Heavens," Sir Robert S. Ball informs us, in the fifteenth thousand, 1890, page 530, " That the moon should bend the same face to the earth depends imme- diately on the condition that the moon should rotate on its axis inprecisely the same period as that which it requires to revolve around the earth. The tides are a regulating power of the most unremitting efficiency to ensure that this condition should be observed." (7) And finally we have what follows from Messrs. New- comb and Holden, at page 164 of their work already referred to at page 27, " The moon rotates on her axis in the same time and in the same direction in which she moves around the earth. In consequence, she always presents very nearly the same face to the earth." And in a footnote to this consequence, add : " This conclusion is often a pons asinorum to some who con- ceive that, if the same face of the moon is always presented to the earth, she cannot rotate at all. The difficulty arises from a misunderstanding of the difference between a relative and an absolute rotation. It is true that she does not rotate relatively D 2 36 New Theories in Astronomy. to a line drawn from the earth to her centre, but she must rotate relative to a fixed line, or a line drawn to a fixed star." In six of the above cases it is distinctly maintained that the moon rotates once on its axis in the same time that it makes one revolution round the earth, and that it is in conse- quence of this rotation that it always presents the same side to the earth. Thus we feel authorised to conclude that their authors did either believe that it does so rotate, or that they entertained some confused idea on the subject, which they did not take the trouble to examine properly, but accepted as a dogma, because some predecessor, with a great name, had stated that such rotation was necessary in order that its same side should be always turned towards the earth. In the seventh case the authors, while actually making the same assertion, try to persuade those who they acknowledge can see that the moon does not rotate on its axis in any sense, that their difficulty in comprehending what is meant by rotation, arises from the misunderstanding of the difference between an absolute rotation and one relative to a line drawn to a fixed star. But they do not attempt to show how this relative rotation has anything to do with or has any effect in causing the moon to present always the same side to the earth ; and leave the story in the same confused state, out of which nobody can draw any satisfactory conclusion. Also, though they dis- tinctly recognise that it does not rotate relatively to a line drawn from the surface of the earth to its centre, they do not include in their general description of the moon anything in any way connected with what would be the consequences of its not really rotating on its axis relatively to the earth. So they leave us the problem in much the same state as they found it, and it is still necessary to show that there can be no actual rotation of any kind on its axis ; and the worst of it is that it is a thing that will have to be done in such very plain language that it will compel people to think of the absurdity of the idea so generally accepted. To begin, it is very difficult to comprehend what the authors, above alluded to, meant by saying that the moon " must rotate relative to a fixed line, or a line drawn to a fixed New Theories in Astronomy. 37 star." It may mean relative to the line itself or to the star to which it is drawn. If it is to the line itself we cannot form any notion of what direction the rotation will have, direct, retro- grade, or otherwise ; and if it is relative to the star itself, then we can see that the relative rotation must depend on what is the position of the star. Should it be placed in the " milky way," we can understand how the moon could show every side it has almost, not quite to the star during every revo- lution it makes round the earth, and how they may look upon it as a relative rotation. But if we draw the line to the pole star we cannot see how the moon can show every side it has to it in every revolution round the earth, so there can be no relative rotation in that case and the " almost, not quite," applies to every star between the pole and the ecliptic. The moon shows only the northern hemisphere, or a little more due to libration of its own kind, to that star, and would have to remove its poles to the equator, and make a new de- parture, in order to show the whole of its surface to that star in every revolution round the earth. Thus it is clear that the explanation given us of the relative rotation, is evidently one of the kind not properly thought out to the end. No one has ever said, or perhaps even thought, that a gin- horse makes one rotation on his vertical axis, in the same time as he makes a circuit round his ring, but, all the same, he keeps his same side always towards the gin, or mill, he is giving motion to. The proof that he does not make any such rotation is easy no proof is really required. But, suppose he is giving motion to a whim for raising ores from a mine, and that his motion is what is called direct. When the cage containing the ore is brought to bank, is emptied, and has to be lowered into the mine again, the horse has then to reverse his motion to retrograde, in doing which he has to make a half rotation on his vertical axis, and turn his other side to the whim. When again the cage has to be raised to bank, he has to resume his direct motion, for which he has to make another half rotation on his vertical axis, but it is this time in the op- posite direction. Thus it is shown that he can only make half rotations, under any circumstances, on his axis,, and these 38 New Theories in Astronomy. in opposite directions, when he changes his motion from direct to retrograde, or vice versa ; and that, when he moves in only one direction he cannot make even one rotation on his vertical axis, however long he may travel round the mill. In the same manner the moon which never turns back in its orbit can never make even one half rotation on its axis, which is all that we have had to prove. It is hardly necessary to ob- serve that its axis is nearly parallel to the earth's, just the same as the horse's is to that of the whim. Neither could any one say that the relative rotation of the horse to a star, or tower, or, say, a bridge, outside of his ring, could have any effect on his revolution round the mill, or his always keeping his same side to it, there being no mechanical connection between them, nor any law of attraction ; and the same is the case between the moon and a fixed star. Now, we may begin to consider what effects must be pro- duced by the moon not rotating on its axis, and we can do so most easily by continuing to work with our gin horse, or some equivalent substitute. It would not cost a great deal of ingenuity to plant a steam engine in the centre of the mill he is supposed to be driving, and to drive with it not only the mill but the horse also at the end of his lever. There might be some dissipation Professor Tate would call it degradation of energy in such an' experiment, but we could get over that by making divina Palladis arte a wooden horse. We might arrange the steam-engine so as to cause the mill to make 27^ revolutions for one made by our wooden horse, and so have a sort of a model of the earth and moon performing their most important relative motions. Then, having got our model ready for action, instead of filling it armato milite we might fill it half full of water. We fill it only half full, because the armed soldiers could not lie on the top of each other in the other horse, and there would be a vacant space above them for air, thus making the resemblance between the two the more similar ; and also because it suits our purpose better, as will soon be seen. We have still to propose that a lot of holes should be supposed to be made in the sides of oitr horse all round, just a little higher than between wind and water. New Theories in Astronomy. 39 Pallas did not order any holes to be made in hers as far as we know, even for ventilation, though we think it would have been an advantage ; but that will not spoil the experiment we are now prepared for. Let the steam-engine be started now and we shall soon see what will happen to the water. As the speed increases it will not be long till it begins to be thrown out, not from the side turned towards the mill but from the one furthest from it ; and if it is increased sufficiently the whole of it will be very soon thrown out. If we could now close up the holes on the side of the horse turned to- wards the mill, it would so happen that a good deal of the air would be expelled also ; and if the speed of the horse were brought up so as to equal that of the moon in its orbit, there would be nothing more, at the most, than traces of air left even in it. The expelling agent in this experiment would, of course, be centrifugal force, and we do not need to exercise our mental faculties very greatly, to comprehend that it is the same force that has driven both air and water away from the side of the moon always turned towards the earth. All the difficulty we have to contend with will be to make sure that the orbital velocity of the moon is sufficient to produce the force required. That the force is exceedingly greater than what is required is proved by the fact, that the velocity with which the moon travels in its orbit is a little more than 38 miles per minute, whereas the velocity of the circumference of a centrifugal machine, used for clarifying sugar, drying clothes, or any other similar industrial purpose, does not require a greater velocity than about one mile per minute, in order to throw everything in the form of water out of the material to be dried, and out of the centrifugal machine itself; and we know that air would be expelled more easily than water, were none re-admitted to supply the place of what was expelled. Here the idea very naturally occurs to any one, that so great a velocity would drive both air and water away, even from the far off side of the moon, into space, but in order to do so the velocity would have to be 120, not 38, miles per minute. Our authority for this statement will be found in "The Nineteenth Century," for August 1896, in an article 40 New Theories in Astronomy. written by Prince Kropotkin, in which he says : " But it appears from Dr. Johnstone Stoney's investigations that even if the moon was surrounded at some time of its existence with a gaseous envelope consisting of oxygen, nitrogen and water vapour, it would not have retained much of it. The gases, as is known, consist of molecules rushing in all direc- tions at immense speeds ; and the moment that the speed of a molecule which moves near the outer boundary of the atmosphere exceeds a certain limit (which would be about 10,600 feet in a second for the moon) it can escape from the sphere of attraction of the planet. Molecule by molecule the gas must wander off into interplanetary space ; and the smaller the mass of the molecule of a given gas, the feebler the planet's attraction, and this is why no free hydrogen could be retained in the earth's atmosphere, and why the moon could retain no air or water vapour." A velocity of 10,600 feet per second is as near 120 miles per minute as there is any use for, which is more than three times as great as the velocity of the moon in its orbit, so there is no possibility whatever of air and water having been swept away from the far off side of it by centrifugal force ; more especially as it ought to be well known that that force is always counteracted by the attractive force of the satellite for these or any other elements. We do not want to discuss the point of whether the mutual collisions of the molecules of a gas could get up such a velocity as would enable them to free themselves from the attraction of the moon, for it looks to us too much like one of those notions that are got up to account for something that does not exist ; but we do want to state our dissent to the conclusion evidently jumped at that because there are hardly any signs of there being air or water on our side of the moon, there can be none on the other. No astronomer, physicist, scientist of any kind, can prove that there is none, simply because he has never been round there to see or make experiments to prove it ; and if there is any one bold enough to make such an assertion, it is only an example of how stupendous a jump to a conclusion can be made. New Theories in Astronomy. 41 When we first read, many years ago, some of the reasons given for there being no water visible on the side of the moon constantly turned to the earth, one of which was that if there ever had been any it must have been absorbed into its body during the process of cooling and consolidation ; and when we had convinced ourselves, by placing two oranges on two ends of a wire and revolving the one round the other, that the moon did not rotate on its axis in any sense whatever, we came to the conclusion that both water and air could be re- moved to the far off hemisphere by centrifugal force. We thought this so simple, so self-evident, and so indisputable an explanation, that every one who had read what we had read must have come to the same conclusion ; so that we were not a little surprised when we saw it stated by " The Times " of September 15, 1893, in its first report of the meeting of the British Association for that year, that Sir Robert Ball had suggested, some time previously, that the " absence of any atmosphere investing the moon is a simple and necessary consequence of the kinetic theory of gases." This at once made us suspect that the theory our theory must have been new, but we could not altogether believe it. It seemed to us passing strange that it should not have occurred to astronomers, from the moment they discovered that they could not find any, or hardly any, traces of air or water on the only hemisphere they could examine ; but it would appear from Sir Robert Ball's suggestion, being even dis- cussed at that meeting, that the notion of their having been removed simply by centrifugal force to the unseen hemisphere, had never been entertained by, to say the least, any one who was present at that discussion. Not satisfied with this conclusion, we proceeded to examine all the books, journals, magazines, and papers we could get hold of, to see whether we could find any indication of such a conception having been published previously, and the nearest approach to anything of the kind having been conceived of by anyone, we found in Chambers's work already referred to at page 134, Vol. I., where we read, " Professor Hansen has recently started a curious theory from which he concludes 42 New Theories in Astronomy. that the hemisphere of the moon which is turned away from the earth may possess an atmosphere. Having discovered certain irregularities in the moon's motion, which he was unable to reconcile with theory, he was led to suspect that they might arise from the centre of gravity of the moon not coinciding with the centre of figure. Pursuing this idea, he found upon actual investigation that the irregularities could be almost wholly accounted for by supposing the centre of gravity to be at a distance of 33 \ miles beyond the centre of figure. Assuming this hypothesis to be well founded, Pro- fessor Hansen remarks that the hemisphere of the moon, which is turned towards the earth, is in the condition of a high mountain, and that consequently we need not be sur- prised that (little or) no trace of an atmosphere exists ; but that on the opposite hemisphere, the surface of which is situated beneath the mean level, we have no reason to suppose that there may not exist an atmosphere and consequently both animal and vegetable life. Professor Newcomb has disputed these conclusions of Hansen, which it is obvious must be very difficult of either proof or disproof." What Professor Newcomb's objections to the conclusions of Hansen were we do not know, but we do know that Mr. Proctor also objected to the " curious theory," as it is called by Mr. Chambers. In his " Poetry on Astronomy," he discusses pretty fully the withdrawal of water from the surface of the moon during the process of cooling and condensation, ascribing the conception of it to four independent authors, namely, Seeman, a German geologist, Frankland in England, Stanislas Mennier in France, and Sterry Hunt in America ; and in a footnote, at page 163, says of Hansen's theory : " The idea was that the moon, though nearly spherical, is sometimes egg-shaped, the smaller end of the egg-shaped figure being directed towards the earth. Now, while it is perfectly clear that on this supposition the greater part of the moon's visible half would be of the nature of a gigantic elevation above the mean level, and would, therefore, be denuded (or might be denuded) of its seas and denser parts of the air covering it, yet it is equally clear that all around the base of this mon- New Theories in Astronomy. 43 strous lunar elevation, the seas would be gathered together, and the air would be at its densest. But it is precisely round the base of this part of the moon or, in other words, round the border of the lunar hemisphere, that we should have the best chance of perceiving the effects of air and seas, if any really existed ; and it is because of the absolute absence of all evidence of the kind, that astronomers regard the moon as having no seas and very little air." Had the idea of centrifugal force ever occurred to Mr. Proctor, he could not have written this last sentence ; for he could not have failed to see that " the border of the visible lunar hemisphere " would be the very place, from which it could most easily remove air and water, after they had got so far down the monstrous elevation ; because there it the centrifugal force would be acting at right angles to the moon's attraction, instead of having to contend against it, as it would have to do in a constantly increasing degree until it arrived at its maximum, just in porportion to the distance the air and water got down to the similar monstrous depression on the other hemisphere, down which the gradient would start off under the most favourable circumstances possible. From what has been said, it is very evident that neither Hansen, Chambers, Proctor, nor any of those whose names have been mentioned by the last, in connexion with the with- drawal of water into the body of the moon by absorption, while cooling and condensing, had ever thought of the possi- bility of air and water having been removed by centrifugal force from the side of the moon turned towards the earth. That it should not have occurred to Hansen seems passing strange, seeing that he had conceived the idea of their possible exist- ence on the hemisphere turned away from the earth, which could hardly fail to make him think of how they got there, and could exist only there ; and the only explanation of his not having perceived the true cause seems to be, that his thoughts were hampered by a sort of confused notion that the moon actually rotates on its axis once for every revolution it makes around the earth, that being, as it were, one of the dogmas of astronomic belief, handed down from 44 New Theories in Astronomy. some great authority of times past, and never properly inquired into. We do not want to question the suggestion, that the absence of any atmosphere investing the moon is a simple and necessary consequence of the kinetic theory of gases though we see that a good deal could be argued against it as we do not consider it to be necessary neither the questioning nor the theory. We have demonstrated clearly, how both air and water could be removed from the side of the moon constantly shown to us, and that is sufficient for our purpose both now and later on ; besides it would appear that the moon really has some sort of an atmosphere somewhere. Following up the quotation, made at page 39, from Prince Kropotkin's article in the " Nineteenth Century " as being the latest information we have on the subject, we are told that " a feeble twilight is seen on our satellite, and twilight is due, as is known, to the reflection of light within the gaseous envelope ; besides it has been remarked long since at Greenwich that the stars which are covered by the moon during its movements in its orbit remain visible for a couple of seconds longer than they ought to be visible if their rays were not slightly broken as they pass near the moon's surface. Consequently it was concluded that the moon must have an atmosphere "... and : " The observations made at Lick, Paris, and Arequipa, fully confirm this view. A twilight is decidedly visible at the cusps of the crescent-moon, especially near the first and last quarters. It prolongs the cusps as a faint glow over the dark shadowed part, for a distance of about 70 miles (60"), and this indicates the existence of an atmosphere having on the surface of the moon the same density as our atmosphere has at a height of about forty miles." What is of interest for us to know is where that " feeble twilight," or, " reflection of light within the gaseous envelope," is seen. Whether it is at what Mr. Proctor calls "the border of the visible lunar hemisphere," on this side of it, or beyond it. It cannot be a difficult matter to decide. It must be beyond it, for the following reasons : If the atmosphere has been driven away to the far-off hemisphere of the moon by New Theories in Astronomy. 45 Centrifugal force, its natural tendency would be to spread out immediately after it had passed the visible border where we have said the centrifugal force would be acting most effect- ively. Also, if all the air at one time belonging to our side of the moon has been driven away to the other, that side must have a double allowance of atmosphere, which, though it does not increase its density at the surface, on account of the centrifugal force, will double its volume, and enable it to extend to a greater proportionate distance in all directions from the border and from the far-off hemisphere. In this way there must be a considerable wedge of atmosphere illuminated by the sun, and visible past the edge of the moon's disc, to reflect a feeble twilight perhaps something stronger towards the earth, and to intercept the light of a star before its edge and that of the moon come into actual apparent contact. But before the wedge becomes thick enough to reflect that light, the reflecting part must be far beyond the edge of the moon's disc. Perhaps the feeble light might be seen more clearly when looked for in the proper place ; quite possibly hundreds of miles beyond the disc. In order to make more clear the truth of what we have said about water and air and more especially the latter being thrown away to the far-off side of the moon by centri- fugal force, we may add the following details : If the force of gravity at its surface is one-sixth part of what it is at the surface of the earth, the pressure of an atmosphere there would be 2 ' 5 Ib. per square inch, if it rotated on its axis ; but as it does not so rotate and is subjected to centrifugal force, the pressure of an atmosphere will vary according to the part of it over which it exists. On the nearest part of the side turned towards the earth, gravity, which we have just seen must be equal to 2 * $ Ib., would be acting in the same direction as centrifugal force, which in its turn is equal to 0*7 Ib. or there- by, and the whole would be 3 2 Ib. per square inch tending to drive off air and water to the far-off hemisphere. But from that place, gravity would gradually diminish its aid till it came to be nil at the disc separating the two hemispheres, where it would have no effect whatever as it would be acting 46 New Theories in Astronomy. at right angles to centrifugal force, and this would be reduced to 0*7 Ib. per square inch. Then, from the edges of the disc forward, on the far-off hemisphere, gravity would begin to act against centrifugal force, or rather vice versa, until it, gravity, got reduced to I 8 Ib. per square inch. Also, as that hemi- sphere must have a double portion of air or atmosphere on it, and as its pressure on any part of it cannot be greater than the I '8 Ib. just mentioned, we can imagine that the double quantity will hang closer to the surface than if there was only one portion. Such being the case the atmosphere would spread out much more rapidly than would be represented by the extension of a triangle starting from the earth and reaching beyond the moon's disc to the farthest limit of the atmosphere ; and thus the wedge, which we have supposed to be visible beyond the edges of the disc may come to have a very considerable thickness. What that thickness may be, and up to what distance beyond the disc the density of the wedge would be sufficient to reflect the light of the sun, it would be very difficult to calculate, but we think it might possibly extend even as far as one-fourth of the radius of the moon because at that point the force of gravity pulling it towards the centre, or the axis, would be very small, and its distance from the axis would be little less than the radius, not over 33 miles and cause it to project over the edges as far, to appearance, as the 70 miles (60") that have been ob- served at Greenwich. This reflected light must be all round the moon not at the cusps only of the crescent-moon and it has occurred to us that it may, most probably does, account for the appearance of what we call " the old moon in the young moon's arms." We know what effect the " earth-shine " has upon the moon at its change, and the brighter ring-shine just outside of it, may very well be caused by the sunlight reflected from the atmosphere far beyond the visible limit of the hemisphere turned to us. In support of this suggestion we may refer to Professor C. A. Young's description, in his " Sun," p. 213, of one par- ticular feature observed at the time of a total eclipse of the sun. He says : " On such an occasion, if the sky is clear, New Theories in Astronomy. 47 the moon appears of almost inky darkness, with just a suffi- cient illumination at the edge of the disc to bring out its rotundity in a striking manner. It looks not like a flat screen, but like a huge black ball, as it really is. From behind it stream out on all sides radiant filaments, beams, and sheets of pearly light, which reach to a distance sometimes of several degrees from the solar surface, forming an irregular stellate halo, with the black globe of the moon in its apparent centre." There can be little doubt, we think, from what is said here, that Professor Young looks upon this "illumination of the edge of the disc " as pertaining to the moon, and upon the " radiant filaments, beams," etc. behind it as belonging to the sun. And in that case the illumination can only be caused by the light of the sun, refracted by the atmosphere belonging to the hemisphere of the moon that is never seen from the earth. We have taken it for granted in what we have been doing ? that the moon has really rotated on its axis, and to some purpose, at some former period of its existence. Some people think otherwise, or that there is at least a doubt about it ; we cannot see even the shadow of a doubt. All that we need to say in support of our opinion is, that there is no other conceivable way of accounting for its perfectly circular form. All the planets are circular, or spheroidal to speak more correctly in form, admittedly in consequence of rotation on their axes ; and if one or two of Jupiter's satellites are not completely circular or spheroidal, it does not stretch our conscience very much to suppose that it is because they have not yet been rotated into form. Saturn apparently has satel- lites still in the form of rings, and there can be nothing out of the way in supposing that all of Jupiter's are not yet licked into shape. The fact that there is no appearance of com- pression on the moon makes us think of why there is none, and the only explanation that occurs to us is, that, as its rota- tion must have come to an end gradually, the compression it must have had when rotating must have disappeared gradually also, by reason of the differences of force in the equatorial 48 New Theories in Astronomy. and polar attractions, drawing in the bulged out, and thus forcing out the compressed parts. This is a notion that will be scoffed at by those who have always thought, and main- tained, that the earth acquired its present form when in a liquid state ; but they have not thought this supposition for it is nothing else out to the very end. Several reasons could easily be given against their opinion, among others the variations in rate of rotation we so frequently see used in favour of other notions ; but we shall content ourselves with the best one of all, which is this : The pressures in the interior of the earth must be so enormous that they are quite sufficient to compress steel, or adamant if that is supposed to be more resistant, into any shape whatever, almost as if it were dough, and there can be no doubt mathematics notwithstanding that the earth has the form, to-day, due to its present rate of rotation. We shall have to return to this subject some time hence, if we live to complete what we have taken in hand. How many things there are, in what is considered to be astronomical science, that have not been properly thought out to the end, and to what strange notions they have given rise ! This one of the rotation of the moon which we have been discussing, has evidently given occasion for the conception of the theory that the absence of atmosphere and seas from the moon is the natural consequence of the kinetic theory of gases ; and the author of the theory, and its supporters, have never, apparently, taken the trouble to think whether their absence from the near hemisphere is a satisfactory and convincing proof of there not being any air or water on the far-off one. In what we have proposed to write many similar examples of want of study will be met with, but we do not intend to call special attention to them, unless it be in cases where we con- sider it to be of some importance to do so. In fact we have already been working on that plan. New Theories in Astronomy. 49 CHAPTER III. PAGE 49 Remarks on some of the principal cosmogonies. Ancient notions. 50 The Nebular hypothesis of Laplace. Early opinions on it. Re- V- ceived into favour. Again condemned as erroneous. 51 Defects attributed to it as fatal. New cosmogonies advanced. 53 Dr. Croll's collision, or impact, theory discussed. 59 Dr. Braun's cosmogony examined. 61 M. Faye's " Origine du Monde " defined. 65 Shown to be without proper foundation, confused, and in some parts contradictory. 70 Reference to other hypotheses not noticed. All more or less only variations on the nebular hypothesis. 71 Necessity for more particular examination into it. WE have thought it worth while to dedicate this chapter to some remarks on cosmogonies in general, and examination into a very few conceived by eminent men ; these forming in our opinion the most attractive matter for those readers who do not pretend to make a study of astromony, but are very desirous to have some knowledge of the most plausible ideas which have been conceived by astronomers, of how the uni- verse, and more particularly the solar system, were brought into existence ; while, at the same time, they are the subjects on which more crude conceptions, more limited study, and more fanciful unexamined thought have been expended, than any others we have met with. Some readers will, no doubt, be able to reject what is erroneous, to speak mildly, but there will be, equally surely, some who cannot do so ; and it must be confessed there are a good many to whom the most com- plicated conceptions, and the most difficult of comprehension, are the most attractive. A great many centuries ago, astromoners and philosophers had already conceived the idea that the sun and stars had been formed into spherical bodies by the condensation of celestial vapours ; but when the telescope was invented, and E 50 New Theories in Astronomy. the nature of nebulae in some measure understood, it was not long till it came to be thought that the matter, out of which the sun and stars were formed, must have been much more substantial in its nature than celestial vapours. Being visible, they were naturally considered to be self-luminous, and consequently endowed with great heat, because the self- luminous sun was felt to be so endowed, though perhaps not with the same degree. Accordingly, astronomers began to form theories, or hypotheses, on the construction of the solar system out of a nebula, which, like everything else, went on each one improving on its predecessor as, through continued observation and study, more knowledge was acquired of the nature of nebulae. The most notable of these cosmogonists were Descartes, Newton, Kant, and Laplace, each of whom contributed valuable contingents to the general work ; which may be said to have culminated about a century ago in the Nebular Hypothesis of the last-named ; for the many attempts that have been made to improve upon it, or to supplant it altogether, have been very far from successful. The hypothesis is about a century old, as we have said, and there may still be many people who can remember having heard it denounced as a profane, impious, atheistic speculation, for it is not over half a century since the ban begun to be taken off it. Sir David Brewster, in his " Life of Newton," said of it, " That the nebular hypothesis, that dull and danger- ous heresy of the age, is incompatible with the established laws of the material universe, and that an omnipotent arm was required to give the planets their positions and motions in space, and a presiding intelligence to assign to them the different functions they had to perform." With others, its chief defect was that the time required to form even the earth in the manner prescribed by it, must have been infinitely greater than six days of twenty-four hours each. In the meantime, geologists had also discovered that, for the forma- tion of the strata of the earth, which they had been examining and studying, the time required for their being deposited must have been, not days of twenty-four hours, but periods of many millions of years each ; and the evidence adduced by New Theories in Astronomy. 51 them that such must have been the case was so overwhelming, that Theology had to acknowledge its force, and gradually to recognise that the days must have been periods of undefinable length. Thus relieved from the charge of heresy, the hy- pothesis rose rapidly into favour, and came to be generally accepted by the most eminent astronomers, subject always to certain modifications, which modifications have never been clearly defined, if at all. It was not, however, allowed to enjoy long the exalted station to which it had attained. Astronomers had begun to consider from whence the sun had acquired the enormous quantity of heat it had been ex- pending ever since the world began, and, after long discus- sion, had corne to the conclusion that by far the greatest source must have been the condensation from the nebulous state of the matter of which it is composed. Having settled this point, it was calculated that the amount of heat derived from that and all other sources could not have kept up its expenditure, at the present rate of consumption, for more than twenty million years, and could not maintain it for more than from six to eight million years in the time to come. Owing in good part to this great difference between the calculations of astronomers and geologists about the age of the earth, the hypothesis began again to suffer in repute, and then all its faults and shortcomings were sought out and arrayed against it. The chief defects attributed to it were : The retrograde motion of rotation of Uranus and Neptune and revolution of their satellites that fault in the former having been noted by Sir John Herschel, in his Treatise on Astronomy already cited ; the discovery of the satellites of Mars which exposed the facts, that the inner one revolves round the planet in less than one- third of the time that it ought to, and that the outer one is too small to have been thrown off by Mars, in accordance with the terms of the hypothesis ; the exclusion from it of comets, some of which at least have been proved, in the most irrefutable manner, to form part of the solar system ; and what can only be called speculations, on the formation of a lens-shaped nebula brought about by the acceleration of rotation caused by condensation according to the areolar E 2 52 New Theories in Astronomy. theory which it is supposed would be enormously in excess of the actual revolution of the inner planets, and of the rota- tion of the sun. Here we must protest against retrograde motion of rotation in any of the members of the solar system being considered as militating against the theory, because Laplace states distinctly, while explaining his hypothesis, that the rotation of the earth might just as well have been retrograde as direct : a fact that some eminent astronomers have not noticed, simply because they have not paid proper attention to what they were reading. We shall have to return to this statement again, and to present the proof of its being true. An idea of how far the hypothesis had fallen into disrepute may be formed from the following extract, from " Nature " of August 4, 1887, of a Review of a "New Cosmogony," by A. M. Clerke, in which it is said : " But now the reiterated blows of objectors may fairly be said to have shattered the symmetrical mould in which Laplace cast his ideas. What remains of it is summed up in the statement that the solar system did originate somehow, by the condensation of a primitive nebula. The rest is irrecoverably gone, and the field is open for ingenious theorising. It has not been wanting. . . . The newer cosmogonists are divided into two schools by the more or less radical tendencies of the reforms they propose. Some seek wholly to abolish, others merely to renovate the Kant Laplace scheme. The first class is best represented by M. Faye, the second by Mr. Wolfe and Dr. Braun " the author of the " New Cosmogony." We cannot pass this quotation without remarking " How glibly some people can write ! " More we do not want to say about it, except that it gave us the notion to examine closely some of the new cosmogonies, which have not been wanting^ to see whether they are better than Laplace's. We have not had the opportunity of knowing what are Mr. Wolfe's amendments, but the Review, just cited, gives us a pretty good notion of those of Dr. Braun, and we have been able to study carefully M. Faye's " Origine du Monde," in which he considers the solar system to have been evolved New Theories in Astronomy. 53 from cosmic matter partially endowed with motion in the form of eddies, whirlwinds, vortices, or tourbillons, which last may comprehend all of them, and even more. We have also studied, with some surprise, in " Climate and Cosmology " Dr. Croll's Impact, or Collision, Theory, and will confine our examination to the three of which we know something, beginning with Dr. Croll's, which we believe to be the oldest of the three. We understand that Dr. Croll accepts the nebular hypo- thesis in all its main features, including the intense heat in which the original nebula is supposed to have existed from the beginning ; and has only invented the collision theory in order to increase its quantity, to suit the demands of geologists for unlimited time, by showing how an unlimited supply of both heat and time may be obtained. But he has incurred an oversight in not taking into consideration the kind of matter in which that unlimited supply of heat was to be stored up whether it would hold it. He wrote in times when some- thing was really known about heat, and we cannot suppose him to have believed that heat could exist independent of matter, or that a gas or vapour could be heated to a high temperature except under corresponding pressure ; but he has evidently overlooked this point, his thoughts recurring to old notions ; and he has fallen, probably for the same reason, into other oversights equally as grave. When showing how a supply of fifty millions of years of sun-heat could be produced from the collision of two half-suns colliding with velocities of 476 miles per second, Dr. Croll says in his " Discussions on Climate and Cosmology," of 1885, at page 301 : " The whole mass would be converted into an incandescent gas " (the handmaid of the period), " with a temperature of which we can have no adequate conception. If we assume the specific heat of the gaseous mass to be equal to that of air (viz. 0*2374), the mass would have a temperature of about 300,000,000 C, or more than 140,000 times that of the voltaic arc." Now, let us suppose the whole mass of the whole solar system to be converted into a gas, or vapour, at the pressure 54 New Theories in Astronomy. of our atmosphere, and temperature of o C., its volume would be equal to that of a sphere of not quite 9,000,000 miles in diameter. Suppose, then, this volume to be heated to 300,000,000 C. in a close vessel, as would necessarily have to be the case, the pressure corresponding to that temperature would be 1,094,480 atmospheres, according to the theory on which the absolute zero of temperature is founded. Without stopping to consider whether air or any gas could be heated to the temperature mentioned ; or the strength of the vessel 9,000,000 miles in diameter required to retain it at the equiva- lent pressure ; if we increase the diameter of the containing sphere to a little more than that of the orbit of Neptune, or, say 6,000,000,000 miles, and allow the air or gas or vapour to expand into it ; then, as the volume of the new sphere will be greater than the former one in the proportion of 9,000,000 cubed to 6,000,000,000 cubed, or as I is to 296,296,296, the pressure of the gas will be reduced to 296,296,296 divided by 1,094,980, that is just over the 2/oth part of an atmosphere ; which, in its turn would correspond to a temperature of a very little more than 273, or what is considered to be* 273 C. above absolute zero of temperature ; or, at all events, to the temperature of space, whatever that may be. Dr. Croll goes on to say at page 302 : " It maybe objected that enormous as would be such a temperature, it would nevertheless be insufficient to expand the mass against gravity so as to occupy the entire space included within the orbit of Neptune. To this objection it might be replied, that if the temperature in question were not sufficient to produce the required expansion, it might readily have been so if the two bodies before encounter be assumed to possess a higher velocity, which of course might have been the case. But without making any such assumption, the necessary expansion of the mass can be accounted for on very simple principles. It follows in fact from the theory, that the expansion of the gaseous mass must have been far greater than could have * This temperature is altogether erroneous, as we shall show in due time ; at present our proof would not be accepted without a demonstration, for which we have not sufficient data. New Theories in Astronomy. 55 resulted simply from the temperature produced by the con- cussion. This will be obvious by considering what must take place immediately after the encounter of the two bodies, and before the mass has had sufficient time to pass completely into the gaseous condition. The two bodies coming into collision with such enormous velocities would not rebound like two elastic balls, neither would they instantly be converted into vapour by the encounter. The first effect of the blow would be to shiver them into fragments, small indeed as compared with the size of the bodies themselves, but still into what might be called in ordinary language immense blocks. Before the motion of the two bodies could be stopped, they would undoubtedly interpenetrate each other; and this of course would break them up into fragments. But this would only be the work of a few minutes. Here then we should have all the energy of the lost motion existing in the blocks as heat (molecular motion), while they were still in the solid state ; for as yet they would not have had time to assume the gaseous condition. It is obvious, however, that the greater part of the heat would exist on the surface of the blocks (the place receiving the greatest concussion), and would continue there while the blocks retained their solid condition. It is difficult in imagination to realize what the temperature of the surfaces would be at this moment. For supposing the heat were uniformly distributed through the entire mass, each pound, as we have already seen, would possess 100,000,000,000 foot-pounds of heat. But, as the greater part of the heat would at this instant be concentrated on the outer layers of the blocks, these layers would be at once transformed into the gaseous condition, thus enveloping the blocks and filling up the interstices. The temperature of the incandescent gas, owing to this enormous concentration of heat, would be excessive, and its expansive force inconceivably great. As a consequence the blocks would be separated from each other, and driven in all directions with a velocity far more than sufficient to carry them to an infinite distance against the force of gravity were no opposing obstacle in the way. The blocks, by their mutual impact, would be shivered into small 56 New Theories in Astronomy. fragments, each cf which would consequently become en- veloped in incandescent gas. These smaller fragments would in a similar manner break up into smaller pieces, and so on until the whole came to assume the gaseous state. The general effect of the explosion would be to disperse the blocks in all directions, radiating from the centre of the mass. Those towards the circumference of the mass, meeting with little or no obstruction to their outward progress, would pass outwards into space to indefinite distances, leaving in this manner a free path for the layers of blocks behind them to follow in their track. Thus eventually a space, perhaps twice or even thrice that included within the orbit of Neptune, might be filled with fragments by the time the whole had assumed the gaseous condition. " It would be the suddenness and almost instantaneity with which the mass would receive the entire store of energy before it had time even to assume the molten, far less the gaseous condition, which would lead to such fearful explosions and dispersion of the materials. If the heat had been gradually applied, no explosions, and consequently no dispersion of the materials would have taken place* There would first have been a gradual melting ; and then the mass would pass by slow degrees in vapour, after which the vapour would rise in temperature as the heat continued, until it became possessed of the entire amount. But the space thus occupied by the gaseous mass would necessarily be very much smaller than in the case we have been considering, where the shattered materials were first dispersed in space before the gaseous condition could be assumed." We have made this very long quotation ; first, because we have not been able to condense it without running the risk of not placing sufficiently clearly the whole of the argumentations employed in it ; secondly, because the purport of the whole explanation set forth is evidently to demonstrate that, by means of the explosions of gases produced by the collision, the matter of the whole mass would be more extensively distributed into space bearing heat along with it than were it gradually melted and converted into vapour ; and thirdly, New Theories in Astronomy. 57 because every argument advanced in favour of the theory of explosions, if carefully looked into, brings along with it its testimony that it has not been studied thoroughly out to the end. Thus the quotation in a great measure saves us that labour. Dr. Croll seems sometimes to demand more from the laws of nature than they can give. He says, at p. 42 of the work cited, that the expansion of the gaseous mass, produced by the collision of the two bodies, must have been far greater than could have resulted simply from the temperature produced by the concussion ; and goes on to show how it the expan- sion might be caused by explosions of gases blowing out blocks of matter in all directions to indefinite distances. But he forgets that these explosions of gases would consume a great part of the heat they contained, that is, turn it into motion of the blocks, and so diminish the quantity produced by the collision, just in proportion to the velocities given to the masses of all the blocks blown out ; so that what was gained in expansion would be lost in heat, and the object aimed at of producing heat for the expenditure of the sun so far lost. Also, that, were the thing feasible, the blocks could not carry with them any of the heat of the exploded gases that might not be used up, and that the heat contained in them derived from the concussion would have time in their flight about two hours at 476 miles per second to melt the matter com- posing them and turn it into vapour, long before even the orbit of Neptune was reached. The heat produced by the explosion of powder in a cannon gives the projectile all the impulse it can, and disappears ; it is converted into motion. It does not cluster round the projectile, nor follow it up in its flight, nor push it through an armour plate when it pierces one. We cannot admit for this reason the possibility of a block of matter flying off into space, with a mass of heat clustering round it, like bees when swarming round a branch of a tree. Thermodynamics does not teach us anything about a mass of heat sticking to the surface of a block of matter of any kind. If the heat were, at a given moment that is, when motion 58 New 7^/ieories in Astronomy. was stopped brought into existence uniformly throughout the entire mass, which, according to the law of conversion of motion into heat and vice versa, would most assuredly be the case, and each pound of the mass possessed 100,000,000,000 foot-pounds of heat, it could not be heaped up on the outer layers of the blocks it matters not whether this means the layers of the outside of the whole mass, or at the outsides of the blocks for the energy of lost motion, converted into heat, must have existed at the centres of the blocks or masses just in as great force as it did at the surfaces when motion was stopped. If each pound of matter carried along with it 100,000,000,000 foot-pounds of heat, that given out by one pound at the centre of a block would be as great as that given out by one pound at its surface ; and the pounds at the surface could not acquire any greater heat from a neighbour- ing pound, because its neighbour could have no greater quantity to give it. Pounds of matter would be melted and vaporized, or converted into gas, just as readily at the centre of the mass or block as at its surface ; and storing up of heat in the interstices of the blocks is rather a strange notion, because we are not at liberty to stow away heat in a vacuum. Besides, it is impossible to conceive how anything in the shape of a block could exist in any part of the whole mass, long enough for it to be blown out into space as a block. But supposing that a block could exist, it would most notoriously be in a state of imstable equilibrium ; and were it then to receive from an explosion of gas, an impulse sufficient to drive it off to the verge of the sun's power of attraction or rather to a distance equal to what that is which would imply a velocity of not less than 360 miles per second, the shock would be quite sufficient to blow it into its constituent atoms. Moreover, as already stated, the heat of the explosion of the gas required to give the impulse would be immediately converted into motion, and disappear ; so that out of the heat produced by the stoppage of a motion of 476 miles per second, that required to produce a motion of 360 miles per second, in each one of the blocks blown out to the distance above mentioned, would be entirely lost to the stock of heat schemed New Theories in Astronomy. 59 for so boldly. Of course, the less the distance from the centre the blocks were blown the less would be the loss, but the fact remains that there would be a loss instead of a gain of heat, in dispersing the matter of two half suns into space by explo- sions of gas. In fine, a given amount of heat will raise the temperature of a given amount of matter to an easily calcu- lable degree, and no more ; and if part of that is expended in expanding the volume of the matter, the whole stock of heat will be diminished by exactly the quantity required to pro- duce the expansions. So that we come back to what we have said at page 54, viz., that when the matter and the heat of the collision of the two half suns were dispersed, under the most favourable circumstances, into a sphere of 6,000,000,000 miles in diameter, the mean density of the matter would be equal to about ^}o tn P art ^ an atmosphere, and its tem- perature what is called 273 C. of absolute temperature, always considering the quantity of the heat to have been 300,000,000 C. Dr. Croll says that if a velocity of 476 miles per second were not sufficient to produce the quantity of heat required, any other necessary velocity might be supposed, but when we consider that his supply of 300,000,000 C. would have to be increased to 82,000,000,000 C., in order to add i C. of heat to the matter dispersed through a sphere of 6,000,000,000 miles in diameter, it seems unnecessary to pursue the subject any farther. We may now take a look at Dr. Braun's Impact Cos- mogony, of which we know nothing beyond what is set forth in the Review in " Nature " already alluded to, but that is enough for our purpose. We understand that he extends his operations to the whole universe, which he conceives to have been formed out of almost unlimited, and almost imponderable, nebulous matter, not homogeneous, but with local irregu- larities in it, which "would lead to the breaking up of the nebula into a vast number of separate fragments." Out of one of these fragments he supposes the solar system to have been formed. This fragment would contain local irregularities also, which through condensation would lead to the formation 66 New Theories in Astronomy. of separate bodies, and these bodies are supposed to have been driven into their present forms, and gyrating movements of all kinds, by centric and eccentric collisions among them- selves, caused by their mutual attractions. Of course anything can be supposed, but in a construction of this kind the idea is forced upon us of the necessity of the active superintendence of the Creator, to create in the proper places and bring in the matter at the exact moment required, and to see that the collisions were directed with the proper degree of energy and eccentricity, to construct the kind of machine that was proposed. To this idea we have no objections whatever, but we would like to see the necessity for it acknowledged. Per- haps Dr. Braun does acknowledge it, but the cosmogony is given to us, it would seem, to show what most probably was the original scheme of construction, and implying that no continual supervision and direction were required during the process. If Dr. Braun could show us some method of attrac- tion, and suspension land variation of attraction, by which some of the separate bodies could be drawn towards each other so as to form a central mass, nebula, or sun, and to give it, by their impacts of collision, a rotary motion ; and how others of the separate bodies could be formed and held in appropriate places, so as to be set in motion at the right moment ; and how they were to be so set in motion without the direct action of the constructor, to revolve as planets around the central mass, we might be able to recognise that a mechanism such as that of the solar system might be brought into existence ; but when we are left to discover all these requisites, and their modus operand^ we find that we might be as well employed in designing a cosmogony of our own. Dr. Braun indulges in somewhat startling numbers in temperature and pressure. He considers that the temperature of the sun, at the surface, may be from 40,000 to 100,000 C., and that it may reach to from ten to thirty million degrees at the centre. In this he may be right for anything we know to the contrary. When riding over a sandy desert, under an unclouded vertical sun, we could easily have believed any- New Theories in Astronomy. 61 thing of the central heat of such a fire, especially when we considered that it was at a distance of ninety-three millions of miles from us. But when he tells us that in the depths of the sun's interior the pressure reaches a maximum of two thousand millions of atmospheres, we " pull in resolution and begin to doubt." Air at that pressure would have a density 2,5^5,984 times that of water, or 456,887 times the mean density of the earth, and we should have a species of matter to ponder over, of which no physicist has ever as yet dreamt. We have been able to study M. Faye's cosmogony in his work on " L'Origine du Monde," second edition of 1885, and can eive a better account of it than of Dr. Braun's. o (i) He repudiates almost all existence of heat in the cosmic matter he is about to deal with, recognising that its temperature must have been very near the point of absolute zero, and also that its tenuity must have been almost incon- ceivable ; so tenuous that a cubic miriametre of it would not contain more perhaps than 5*217 grammes in weight. And very properly, we think, he looks upon the solar systems as having, at one time, formed a part of the whole universe, all of which was brought into existence, created, more or less, about the same time. In this universe, he considers that the stars have been formed, as well as the sun, by the progressive concen- tration of primitive materials disseminated in space, which con- ception gives rise to a totally new notion of the most positive character : viz. that each star owes to its mode of formation a provision of heat essentially limited ; that it is not permissible, as Laplace thought he could do, to endow a sun with an in- definite amount of heat ; and that what it has expended and what it still possesses, depend upon its volume and actual mass. And also that the primitive materials of the solar system were, at the beginning, part of a universal chaos from which they were afterwards separated, in virtue of movements previously impressed on the whole of the matter ; and sums up his first ideas in the following manner or theorem : " At the beginning tJie universe consisted of a general chaos, 62 New Theories in Astronomy. of extreme tenuity, formed of all tJie elements of Chemistry more or less mixed and confounded together. These materials under the force of their mutual attractions were, from the beginning, endoived with diverse movements which brought about their separation into masses or clouds. These still retained their movements of rapid translation, and very gentle interior gyra- tions. These myriads of chaotic fragments have given birtJi, by means of progressive condensations, to the diverse worlds of the universe? (2) So much for the formation of the universe, including, of course, the solar system, for which he acknowledges the necessity for the intervention of a creating power, because it is impossible to account for it simply by the laws of nature ; and adds : It is unnecessary to say that the universe is an indefinite series of transformations, that what we see results logically from a previous condition, and thus necessary in the past as in the future ; we cannot see how a previous condition could tend towards the immense diffusion of matter, to the chaos out of which the actual condition has arisen ; and that it is, therefore, necessary to begin with a hypothesis, and postulate of God, as Descartes did, the disseminated matter and the forces which govern it. (3) From dealing with the universe, M. Faye comes to the formation of an isolated star, and begins with an entirely ideal case, that of a spherical homogeneous mass, without interior movement of any kind, and concludes that the mole- cules would fall in straight lines towards the centre ; that the mass would condense regularly without losing its homo- geneity, and would end in producing an incandescent sphere perfectly immovable ; and that that would be a star, but a star without satellites, without rotation, without proper movement. This not being what was wanted, he goes on to show how, previous to its separation and complete isolation from the universal chaos, such a mass would possess, and carry with it when separated, a considerable velocity of rotation, and would still retain the internal movements it had acquired from the attraction of the other masses with which it had been pre- viously in contact ; and how the molecules, drawn towards the New Theories in Astronomy. 63 centre in obedience to gravitation, would not fall in straight lines but in concentric ellipses. (4) From this state of affairs, two very different results might arise. One, that the molecules might resolve themselves into a multitude of small masses without the centre acquiring a preponderating increase. The other, that the central con- densation might greatly exceed the others, and there would be formed a central star accompanied by a crowd of small dark bodies. M. Faye accepts the second result, in which case the ellipses described by the small bodies, now become satellites, would, as the central mass increased in preponder- ance, have one of their centres at the centre of the prepon- derating mass, and their times of revolution would vary from one to another in conformity to the third law of Kepler. (5) For the formation of the solar system M. Faye finds that it is of little importance whether the movements of bodies around the sun be very eccentric or almost circular ; the first cause is always the same. They arise from the eddies, tour- billonnementS) they have brought with them from their rectilinear movements in the primitive chaos. But the circle is such a particular case of the ellipse, that we ought not to expect to see it realized in any system. It is therefore necessary that, among the initial conditions of the chaotic mass, one should be found which would prevent the gyrations, eddies, from degenerating into elliptical movements, and which has at first made right, and afterwards firmly preserved, the form, more or less circular, in all its changes. (6) For the formation of circular rings he gives us the following conceptions : In order that a star should have com- panions, great or small, circulating round the centre of gravity of the system, it is necessary that the partial chaos from whence it proceeded should have possessed, from the beginning, a gentle eddying movement affecting a part of its materials. Besides, if the partial chaos has been really round and homo- geneous, we shall see that these gyrations must have taken up, and to some extent preserved, the circular form. He then requests the reader not to lose sight of the feeble density of the medium, in which a succession of mechanical changes are 64 New Theories in Astronomy. to be brought about ; and not to conclude that that density v/as such that a cubic miriametre of the space occupied by it might not contain 3250 grammes of matter, as he stated in the preceding chapter (we think he said 5217 grammes), but that it might contain only 3 grammes or even less. And adds that in such a medium, the small agglomerations of matter which would be formed all through it, would move as if they were in an absolute vacuum, and any changes in them would be produced extremely slowly. (7) Then he goes on to say that the gyrating movements belonging to the chaotic mass, would have very little difficulty in transforming a part of a motion of that kind into a veritable rotation, if this last were compatible with the law of the internal gravitation ; that it is the nature of that kind of masses to only permit, to the bodies moving in them, revolu- tions, elliptic or circular, concentric and of the same duration ; that therefore notable portions of the gyrating matter could take the form and movements of a flat ring, turning around the centre with the same angular velocity, exactly as if this nebulous ring were a solid body ; that all the particles which have the proper velocity in the plane of the gyrations, will arrange themselves under the influence of gravitation in a flat ring with a veritable rotation around the centre ; that any other parts having velocities too great or too small, will move in the same plane, describing ellipses concentric to the ring ; that if the ellipses are very elongated the materials composing them will approach the centre, where they will produce a pro- gressive condensation, communicating to the central globe formed there a rotation in the same plane with the primitive gyrations ; and finishes off the whole scheme by specifying the first results to be : (i) The formation of concentric rings turning in one piece, in the manner of a solid body, around a centre almost empty (d'abord vide) ; and (2) A rotation in the same direction, communicated to the condensation which would be produced, little by little, by means of matter coming in, partly, from regions affected by the internal eddyings (tonrbillonnements). (8) It is unnecessary to go any farther, and take note of jj UNIVERSITY V OF ^/ New Theories^^^j^^^my. 65 his method of the formation of planets and satellites from rings, as it is much the same as what we have seen described by others who have written on the same subject ; only inter- preted by him in a way to suit his own purposes, and in which interpretation he does not do full justice to Laplace, through not having paid sufficient attention to nis explanation of how planets could be formed out of rings. Except in so far as to note that all along he has considered that rings were formed, and even those nearest to the centre condensed into globes, long before the central condensation had attained any magnitude of importance, or assumed any distinctive shape, and that afterwards all the disposable matter of the rings and also all the exterior matter that had not formed part of what was separated from the original universal chaos, had fallen in towards the small central mass, and so completed the forma- tion of the sun last of all. We shall now proceed to make a few remarks with respect to this condensation of M. Faye's cosmogony, which we think we have made without adding to or omitting anything of importance that we have met with in his work, for which purpose we have numbered the paragraphs containing it, in the last six pages, in order to do away with the necessity of repeating the parts to which we refer. No. I. All those who believe that "the solar system did originate somehow, by the condensation of a primitive nebula," agree with M. Faye in considering that the density of the nebulous matter must have been extremely low, and some of them seem almost to vie with each other in showing how great must have been the degree of its tenuity ; but M. Faye is one of the few who, paying due respect to the law of the inter- dependence of temperature and pressure in a gas or vapour, maintain that it must have been almost devoid of temperature, and we have to acknowledge that he is in the right. Then we believe that his assumption, that the whole universe of stars, including the sun, was created, humanly speaking, about the same time, is shared by the great majority of those who have thought at all seriously on the subject. Also, we agree with him firmly in his statement that each star and we F 66 New Theories in Astronomy. add planet, satellite, etc. was originally supplied with an extremely limited quantity of heat, and that what it has expended and what it still retains has been derived entirely from the condensation of the original cosmic matter out of which it was made. With regard to his theorem : we cannot follow him in his statement that the diverse movements caused by the mutual attractions of parts of the original universal mass of cosmic matter, have brought about its separation into myriads of fragments ; nor how these fragments could carry with them a rapid movement of translation, unless the whole universal mass was endowed with a rapid movement of translation through space, in which case we think that such a motion would have had no greater particular effect in producing new forms of motion in the fragments, than if the whole had been created in a state of rest. Stray movements of translation might give rise to collisions among the multitude of fragments, and perhaps that was one of the modes of formation into suns through which they had to pass ; but we cannot follow it out. Neither can we see clearly how translation could be effected of one mass into the space occupied by another mass unless empty spaces were reserved for that purpose from the begin- ning. Without that, translation could not exist : it would be collision. No. 2. We have nothing to object to what is said in this paragraph ; except that a rotating sphere might have been postulated at once, in imitation of Laplace, instead of trying like Descartes to join fragments together, endowed with movements so adjusted that, among the whole of them, they would produce in the whole mass, when united, the kind of movement that was wanted. No. 3. To the ideal case of the formation of an isolated sun from a homogeneous mass without interior movement of any kind, we cannot agree in any way. The molecules of matter would not, could not, fall in towards the centre in straight lines. Their mutual collisions would drive them generally in curved lines in all directions as they fell in, which would create new internal movements ; and these movements New Theories in Astronomy. ' 67 would prevent the possibility of the formation of an immov- able incandescent sphere such as is described. There could be no immobility in the interior of a sun, as long as its temperature was sufficient to keep the surface incandescent. But we cannot give our reasons here for this assertion to most people they will, we think, occur at once because we have a long road to travel before we can do so. When M. Faye abandons the isolated case, he leaves us without giving us any help, to conceive for ourselves how the mass would possess and carry with it a considerable velocity of rotation, and still retain the internal movements it had acquired from the attraction of the other masses of the uni- versal chaos with which it had been in contact ; and also how the molecules drawn towards the centre would not fall in straight lines but in concentric ellipses. And this last we have to do without his giving us any reason why the molecules should fall in towards the centre at all ; or rather in spite of the fact that one of his principal ideas would lead us to ex- pect exactly the contrary, as we shall see presently. No. 4. Here he places before us again, two cases in one of which the molecules might resolve themselves into a multi- tude of small masses, without the centre acquiring any preponderating increase ; and the other where the central condensation might greatly exceed the others, and there would be formed a central star accompanied by a crowd of small dark bodies, now become satellites, describing ellipses around the central preponderating mass. This second case he seems, for the time being, to accept as the most probable ; but it is strangely at variance with what he sets forth after- wards. He does not give us the least hint as to why or how the satellites acquired their various times of revolution, but only assumes that they did so ; and we are very sure that it was not the third law of Kepler that was the agent in the case, however much it might suit his purpose. No. 5. Although this part of his exposition is dedicated to the formation of the solar system, all that M. Faye says is that it is of little importance whether the movements of bodies around the sun be very eccentric or almost circular ; F 2 68 New Theories in Astronomy. and that among the initial conditions of the chaotic mass, all that we require is that one should be found which would prevent the gyrations from degenerating into elliptic move- ments, and which had first put right and afterwards firmly preserved the form, more or less circular, in all its changes. But he does not make any attempt to show what that one condition is, and allows us to find it out for ourselves. No. 6. What M. Faye says about the formation of circular rings is more or less a repetition of what he has adduced, to explain all the other movements which he has derived from the universal chaos ; and which he seems to think sufficient to account for such movements being nearly circular. For our part we do not think they are sufficient, and he does not show us how they influence each other to bring about the final movements he wants to present to us. We duly take note of the tenuity of the cosmic matter on which he operates, which at 3 grammes in weight to i cubic miriametre would correspond to one grain in weight to 771,947,719,300 cubic feet of space, or I grain to a cube of 9173 feet more than 3000 yards to the side. We do this in order to remind him of what he says at page 151 of his work, when dealing with the rotation of the Kant-Laplace nebula namely, that it is impossible to comprehend how an immense chaos, of almost inconceivable tenuity, could possess such a rotation from the beginning, and that for want of that inadmissible supposition nothing remains to fall back upon but the mouvements tourbillonnaires of Descartes. Thus he wants us to believe that his tourbillons could move in straight or curved lines, have motions of translation, could attract, restrain, and drive each other into all sorts of move- ments with the tenuity he has indicated ; but that Laplace's nebula, with a density of I grain to a cube of 90 feet or at most 1 50 feet to the side, could not be conceived to have the single movement of rotation. And lastly, we repeat that if the centre of the chaos was almost empty, we do not see what induced the cosmic matter to fall into it in elliptic orbits. Nos. 7 and 8. In these paragraphs, the main features are repetitions of the simple assertions made in all the others, that New Theories in Astronomy. 69 certain movements possessed by matter in one state would produce other movements in another state, without attempting to show how they all came to so far coincide with each other and form one harmonious whole, with movements in almost one single direction. It is clear that one side of the separated chaos might have acquired motion in one direction from the universal chaos with which it had been in contact, and that the opposite side might have acquired motion in exactly the opposite direction from the original chaos with which it had been in contact ; and we are left to find out how these came to agree with each other in the end. And, going back to the beginning, we are left to find out where the mass, out of which he constructs his solar system, was stowed away, after it was separated from the original universal chaos. We can conceive of its being separated by condensation, in obedience to the law of attraction, from the surrounding chaos, in which case it might fall towards a centre, or that some parts of it might come to revolve round each other, and that finally the whole of these parts might come to rotate about a common centre ; but that is evidently very different from the mode of formation of the solar system which M. Faye has advocated. It comes to be by far too like the nebula which Laplace supposed to be endowed with rotary motion from the beginning, probably because he did not see, or did not take the trouble to see, how such a motion could be produced. In any case, Laplace did not consider that the primary motion of rotation was the most important part of his hypothesis ; neither was it, as it seems to have been in the case we have been considering. And he did not go much further than M. Faye in postulating primary motion, only he did it in a more effectual and business-like manner. He drew on the bank at once for all the funds he required, instead of having to draw afresh every time he found himself in difficulties, as has been the lot of his critic and successor. Finally, M. Faye tries to show that after all his rings, flat or otherwise, converted or not converted into globes, had been formed according to his ideas, the greater mass by far of the chaos had fallen into the centre, and had formed the sun there 70 New Theories tn Astronomy. last of all. Now, if the preponderating mass of the chaos had been outside of the field of his operations, up to the period when all his planets, satellites, etc. were formed, or at least laid out, it is more natural to suppose that the matter inside of his structure, if there was any, would be drawn outwards by the attraction of the greatly preponderating mass outside, than that any portion of it should have fallen in, in elongated ellipses, towards the insignificant mass that he supposes to have been inside his structure. This, of course, would be nearly exactly the reverse of the mode of formation he was trying to demonstrate, and clearly shows that he was working on unsound principles from the beginning to the end of his cosmogony. It had never occurred to him that matter could be attracted outwards as well as inwards, most probably because it would seem to htm ridiculous to imagine that anything in the universe could gravitate upwards. There are other theories of the formation of the solar system from meteorites and meteors, giving us the idea of its being made out of manufactured articles instead of originally created raw material, which does not in any way simplify the process. In some of them, the inrush of meteor swarms is invoked as the cause of gyratory motion, which places them in much the same category as impact theories. We know that broadcloth is made out of woollen yarn, but we also know how the yarn is made out of wool, and how it is woven into the cloth, whereas we are not told by what process, or even out of what the meteors and meteorites are made, although some of them are said to have thumb-marks upon them. All these theories and cosmogonies may be very appro- priately classified as variations of the nebula hypothesis, and like variations in another science, may be very brilliant, scientific, imaginative, grand, but after all the flights of fancy exhibited by them are set before us, we feel in a measure relieved when a return is made to the original air. They all assume original motion, varied, accidental, opportune, more dependent upon the will of the cosmogonist than on the laws of nature, which tend to confound rather than enlighten any one who tries to understand and bring them, mentally, into New Theories in Astronomy. 71 actual operation. Laplace assumed rotary motion for the whole of his nebula, and was thus able to account at once for the relation which exists among the planets in respect of dis- tance from, and period of revolution around the sun arising from the original rotation of the whole mass in one piece a result which, in any impact theory, has to be accounted for separately, and, in plain truth, empirically in each case, and at each step. Seeing, then, that we have not been able to find any cosmogony, or speculation, that gives us a more plausible idea of how the solar system has been formed, we shall try whether from the original nebula as imagined by Laplace, it is possible to separate the various members, and form the system in the manner described in his celebrated hypothesis. In other words, we shall endeavour to analyse the hypothesis. 72 New Theories in Astronomy. CHAPTER IV. PAGE 72 Preliminaries to analysis of the Nebular hypothesis. 73 Definition of the hypothesis. 75 Elements of solar system. Tables of dimensions and masses. 78 Explanation of tables and density of Saturn. 79 Volume, density and mass of Saturn's rings, general remarks about them, and satellites to be made from them. 79 Future of Saturn's rings. 80 Notions about Saturn's satellites and their masses. 8 1 Nature of rings seemingly not well understood. 81 Masses given to the satellites of Uranus and Neptune, Explana- tions of. 82 Volumes of the members of the solar system at density of water. PRELIMINARIES TO ANALYSIS OF THE NEBULAR HYPOTHESIS. IT may be thought that there is little benefit to be derived from analysing an hypothesis which has been declared, by very eminent authorities in the matter treated of, to be erroneous in some points of very serious importance ; but hypotheses are somewhat of the nature of inventions, and we know that it has often happened that many parties, aiming at the same invention, have altogether failed, while some other person using almost exactly the same means as his predecessors, has been entirely successful in his pursuit. How many times has it been pointed out to us, that if such a person had only gone one step further in the process he was following, or had only studied more deeply the matter he had in hand, he would have anticipated by many years one of the greatest discoveries of the age ! In some cases the failure to take that one step was occasioned through want of knowledge acquired long years afterwards ; whereas we think that in the case we have in hand, it can be shown that the want of knowledge acquired many years after he had formulated his hypothesis, or if New Theories in Astronomy. 73 otherwise, the want of faith in what he knew, enabled Laplace to construct an edifice which otherwise he could hardly have convinced himself could be built up in a practical form. We think also that if he had made the proper use of the know- ledge he must have had of the law of attraction, he would have seen that no nebula could ever have existed such as the one he assumed, extending far beyond the orbit of the re- motest planet. Furthermore, we think it can be shown that if he had thoroughly considered what must have been the interior construction of his nebula, he would have found one that would have suited his hypothesis in the main point, viz. condensation at the surface, at least equally as well as endow- ing it with excessive heat. But to be able to show these things our first step must be to analyse the hypothesis, to examine into it as minutely and deeply as lies in our power. For this purpose it will be necessary to define what the hypothesis is. Many definitions have been given, more or less clear, and it would be only a waste of time to try to set forth Laplace's own exposition of it, with all its details, which he had no doubt studied very carefully. But in those defini- tions that have come under our observation, several of the conditions he has specified are wanting, or not made suffi- ciently prominent ; so instead of adopting any one of them we will make a sort of condensation of the whole, adding the conditions that have been left out ; because the want of them, has been the cause of mistaken conceptions of the evolution of the system having been formed by very eminent astro- nomers. Our definition will therefore be as follows : I. It is supposed that before the solar system was formed the portion of space in which its planets and other bodies now perform their revolutions and other movements, was occupied by an immense nebula of cosmic matter in its most simple condition of molecules or atoms somewhat of a spherical form, extending far beyond its present utmost limits, and that it was endowed with excessive heat and a slow rotary motion round its centre ; which means that while it made one revolu- tion at the circumference it also made one at the centre. The excessive heat, by counteracting in a certain measure the 74 New Theories in Astronomy. force of gravitation, kept the molecules of matter apart from each other ; but as the heat was gradually radiated into space, gravitation became more effective, and then began to condense and contract more rapidly, by which process its rotary motion was, in accordance with the areolar law, gradually increased at the surface, in the atmosphere of the sun, where the cooling took place, and condensation was most active ; and the in- crease of rotation was propagated from there towards the centre. (2) As the contraction and rotation increased a time or times arrived, when the centrifugal force produced by the rotation came to balance the force of gravitation, and a series of zones or rings were separated from the nebula, each one of them continuing to rotate revolve now around the central mass, with the same velocities they had at the times of their separation ; until at last the nebula became so contracted that it could not abandon any more rings, and what of it remained condensed and contracted into a central mass which ultimately assumed the form of the actual sun. (3) In the meantime, or following afterwards, each one of the rings which were abandoned by the nebula, acquired, through the friction of its molecules with each other, an equal movement of revolution throughout its entire mass, so that the real velocities of the molecules furthest removed from the centre of the nebula were greater than those of the molecules nearest to its centre, and the ring revolved as if it were in one solid piece. Arrived at this stage the rings broke up and formed themselves into smaller nebulae, each of which con- densed into a globe or planet, and continued to revolve around the central mass in the same time as its mass had done when in the form of a ring. And some of these sub-nebulae, imitat- ing the example of their common parent more perfectly than others, abandoned in space in their turn smaller rings which in the same manner condensed, broke up, and formed them- selves into smaller globes or satellites ; all, as far as we know, except the rings of Saturn, which have not as yet been con- verted into satellites. (4) All of these bodies, planets, satellites, and rings were New Theories in Astronomy. 75 1 W 1^* tO VO VO C^ 00 vO vo oo III ^ r- F ? ? r^ ? O VO CO vo 5J.S OO N VO OO >-> CO ON VO oo oo vb oo i> O c N to VO t^ CO VO .2 "'S 3 -T ^ o" ?0 A OJ * "o j 1 1 1 1 ! ! 1 1 1 i CO C o O to vO vo N ^\ ^* vl CO 1 4j Q N ^ -* O ^ M O C^ to i-^ vO vO ^ VO CO oo 2 C/5 1) C - o\ nT ^-T ON ^.J. vo o*\ vo M s 5 M_( -^j- H fe G 4 Q ^7 C J l to o O O oo oo t-i vo >-> VO OO vo Tt- OO OO vo "- 1 I co vo CO f ft CO 41 tfl >H vb W 1 vo rj- t-i b ^ J^ s ^ Wrn H a g a < O t^. O vo CO VO O ^- vC co co N O OO N CO CO vO O v ' ON n j-> >< oi OT Q _s OO OO N CO KH VO N CO CO O ON t^ OO CO " vO VO VO 1 I J < < 3 OO vo CO ON CO ^< CO 00 | f 3 o H M co O c * vO N N ON 1 t CO B _d ^ : ft ff 2" vo H4 3 N CO O H a 1^^* N " < O t^i VO CO ^_ 1 8, co vo ON 3- o oo. oo oo K w '-' N 8 I . i T8 Z * * > ^ D ^ (A; O ^ d 3 q 1 1 1 1 1 1 I 2 CO 1 a, New Theories in Astronomy. a 00 vo !|i 00 N CO 2 >5* Js VO t- ^ CO M "o+-^ N CO t>- 115 J eg ON CO vo 00 vo ON I** ON co vO O vo t~ ^h c vo d \ ~ - ,. vo 00~ 00 rf |JB 1 *%* n Q * "tf- 35 rh O t^ *i 'o' 5 VO v^-% ON t^ vo t~ vO vO t*^ vO *M ^ 00 5 O r^ t>^ CO VO CO *- r^ vo ^ vO O ON ON H vO~ > W CO M (S 3 vO ? II ^ *o 3- 2S ^ CO Jj CO *^ C^ N^ w t-. b I g 1 t 1 ? 5I VO ^N OcoONt^- OOOOOvOrt- ^OO .'VOCON N ^O VOLOVOOO O CO CO w ^ 5vvO h O ** M 'O ^vo^-rl-Ti-t^vovo VO l i t^>. "^ oO ^" ^ vo ^ d vO vo vO O "* vo ^j C^ v^ 4 ON OO OJ ^^ Co ^O ON OO O CO ^ ir> , vo rj- 1-1 co ^, 00 CO CO - B -' O c^ ON vo ON O Q Q Q Q vO VOONCOM O^.OOOOij.. HH NOTt-ON OvovoNCO^ | t|* N MNCON i-i mco M an Distance 3m Primary in Miles. 00 co^cooo OOOOOOOO OO t^ vo GO c^ O vo t"* vo CO vO t^ CO vO W t^* ON C^ vo ON ^" ^" ON O N N^VO>-l h^MHHMCOt^O CO S* M HH N 1 v cS ^ . . . . g . . . . . 'HI I 1 1 1 1 1 1 S i W O U SWHQP^HE 1 New Theories in Astronomy. 77 I 11 >-" N CO *|i .. 1 ^B ON fil 3 IJ c eg II 2| i Volume o Cubic 1 CO "5 < M S ifl .'... & _c t^ t^ oo |N ^- JC TJ- vo .H'S if) vr> ON O rr t^ 00 O O O vO OO ji N ON O ^ vn n" W l/^ VQ CO tO j O O O O O CO ^* ON O ^O ^ ON N to HH 10 O ON .s < 2 a 3 I . . . o 8 S Q 1 1 1 1 1 1 S .- I l i 78 New Theories in Astronomy. supposed to revolve around their primaries, and to rotate on their axes, in the same direction viz., from right to left, in the opposite direction to the hands of a watch. In addition to the above definition it is necessary to give some sort of description of the various parts of the machine or system which has to be made out of the nebula, with their positions, dimensions, and details. This we believe will be made plain enough, in the simplest manner, by Table No. I., taken and calculated from the elements of the solar system given in almost all astronomical works, from which we have selected what be believe to be the most modern data. The construction of this table requires some explanation on account of its being made to show complete results from incomplete data. There has been no difficulty with the sun, the major planets, and the satellites of the earth and Jupiter, but for the minor planets, the satellites of the three outer planets, and the rings of Saturn, we have been obliged to exercise our judgment as best we could. There being almost no data whatever of the dimensions and densities of the minor planets, to be found, we have been driven in order to assign some mass to them, to imagine the existence of one planet to represent the whole of them (in fact Olbers's planet before it exploded), which we have supposed to be placed at the mean distance of 260,300,000 miles from the centre of the sun ; and we have given to it a mass equal to one-fourth of the mass of the earth, that being, in the opinion of some astronomers, the greatest mass which the whole of them put together could have. This assumption we shall explain more fully at a more suitable time. In the case of Saturn the diameters of two of the satellites are wanting which we have assumed to be the same as those of the smallest of those nearest to them, and thus have been able to compute the volumes of the whole of them ; but we have not been able to find any statement anywhere of their densities, and to get over this difficulty we have reasoned in the following manner. The density of the moon is very little over two-thirds of New Theories in Astronomy. 79 that of the earth, while that of the satellites of Jupiter varies from a little more than the same to a little more than twice as much as the density of their primary. Why this difference ? To account for it we appeal to the very general opinion of astronomers, that the four inner planets are in a more advanced stage of their development, or existence, than the four outer ones. In this way it is easy to conceive that the earth has arrived at the stage of being more dense than its satellite ; while in the case of Jupiter, his satellites being of so very much less volume than their primary, have already arrived at a higher degree of development. Carrying this motion forward to Saturn, we have supposed that from his being considerably less dense than any other of the outer planets quite possibly from having been formed out of material comparatively (per- haps not actually) less dense than the others his satellites may not have condensed to a greater degree than his own mass, and we have, therefore assumed their density, that is the density of the volume of the whole of them, to be the same as that of their primary. To determine some mass for the rings of Saturn, is a much more intricate matter than for his satellites, and presents to us some ideas facts rather which had never before crossed our imagination. The most natural way to look upon these rings is to suppose that they are destined to become satellites at some future time. All the modern cosmogonies that have come under our notice are founded upon the idea that rings are the seed, as it were, of planets and satellites, and if those of Saturn have been left, as it has been said, to show how the solar system has been evolved, it cannot be said that the supposition is not well founded. In this way we are led to speculate upon how many satellites are to be made out of the rings before us. Considering, then, that the nearest satellite is 120,800 miles from the centre of Saturn, leaving only 83,500 miles between his surface and that of Mimas, and also that the distances between satellites diminish rapidly as they come to be nearer to their primaries, there is not room to stow away a great number of satellites. On the other hand, seeing that there are at least three distinct rings, we cannot reasonably do 8o New Theories in Astronomy. less than conclude that three satellites are intended to be made out of them. But let the number be what it may, all that we have to do with them for our present purpose is to assign some mass to them. With this view, we have given, arbitrarily, to each one of the three we have supposed, a volume equal to that of one of the satellites of 500 miles in diameter, that is, about 65,000,000 cubic miles, and we have supposed their density to be the same as that of water, instead of that of the planet Thus, in the table, we have assigned to the three a mass of 195,000,000 cubic miles at density of water, which would be more than sufficient to make four other satellites for the system of 500 miles in diameter each, and of the same density as the planet. For the table referred to we have calculated the areas of the three rings to be 152,110,800,172 square miles, and we have assumed the thickness as 90 miles, that is about two-thirds of that estimated by Chambers in his hand- book of Astronomy, but almost the same as that given by Edmund Dubois ; nevertheless their total volume comes up to 1,369,062,060,480 cubic miles, which reduces their average density to 0*0001425 that of water, to make up the mass of 195,000,000 cubic miles at the density of water, which we have adopted for the three. This density corresponds to very nearly one-tenth of that of air, which, however strange it may appear to us, may be considered to be a very full allowance, seeing that we shall find, later on, that the planet itself was formed out of matter whose density could not have been more than one twenty-six millionth part of that of air. All the same, it is hardly matter that we could liken to brickbats. After being driven to this low estimate of density, which startled us, we referred to an article in 339557 J I 55 15 cubic miles for his system at the same density as the nebula ; therefore, substracting this amount from i,348,720,i86,335 15 weget I,347,38o,629,i8o 15 cubic miles as the volume to be condensed into the succeeding nebula which we shall call Asteroidal, the dimensions of which we can determine in the following manner, although only very approximately. According to the nebula hypothesis, there must have been a ring detached from the nebula for the formation of the Asteroids, as well as the formation of the other planets. So, in order to be able to assign elements for that ring, corre- sponding to those we have found for the others, we shall suppose the whole of them to have been collected into one representative planet, at the mean distance from the centre of the nebula of 260,300,000 miles, more or less in the position denoted by the number 2.8 in Bode's Law ; also its mass to have been one-fourth of that of the earth, or 367,792,000,000 cubic miles at density of water, which, in the opinion of probably most astronomers, is a considerably greater mass than would be made up by the whole of them put together discovered and not yet discovered. With the above distance from the centre of the nebula, the divisionary line between the Jovian and the Asteroidal nebulae would be 372,000,000 miles from the said centre, and the diameter of the latter 744,000,000 miles in consequence. We know that some of the Asteroids move in their orbits beyond this supposed divisionary line, and it may be that when we come to determine the divisionary line between the supposed Asteroidal and the Martian nebulae, some of them may revolve in their orbits nearer to Mars than that line, but that will not interfere in any way with our operations, because we are only dealing with the whole of them collected into one representative. For finding the dimensions of the ring for Jupiter's system, we have the mean diameter of his orbit as 967,356,000 miles, New Theories in Astronomy. 93 which makes its circumference to be 3,039,045,610 miles in length. Therefore, dividing the volume of the ring as found above, viz. 1,339 557, 155 15 cubic miles by this length, the area of its cross-section comes to be 440,782,188,524,000 square miles, which divided in turn by the breadth of 313,400,000 the difference between the radii of the Jovian and Astcroidal nebulae, or 685,400,000 less 372,000,000 makes the thickness of the ring to have been 1,406,771 miles. But, as before, the inner edge of the ring had become 6-2484 times more dense than the outer edge, so that the average thickness would be only 450,282 miles. ASTEROIDAL NEBULA. The volume of the nebula after the separation of the ring for the system of Jupiter having been 1, 347,380,629, i8o 15 cubic miles, this volume has to be condensed into the volume of the Asteroidal nebula of 744,000,000 miles in diameter and consequently of volume of 215,634,925, 373, 133, 82O 9 cubic miles. Then if we divide the first of these volumes by the second, we find the density to have been increased 6 '24.84 fold, as used above for the average thickness of Jupiter's ring. But the density of the Jovian nebula was 2,794,417,420 times less than water, dividing which by 6 '2484 makes the Asteroidal nebula to have been 447,218,905 times less dense than water. This again divided by 773*395 makes it 578,254 times less dense than air, which will give us 0*00047384 as its abso- lute temperature or the same as 273 '99952616. Next, from the Asteroidal nebula 774,000.000 miles in diameter, volume of 2I5,634,925,373,I33,82O 9 cubic miles, and density 447,218,905 times less than water, we have to deduct the volume of the whole of the system which in Table No. II. we have supposed to have been 367,792,000,000 cubic miles at density of water. Multiplying this by 447,218,905 we get the volume to have been 1 64,482,7 17,2OO 9 cubic miles for the ring at the same density as the nebula ; so, deducting this quan- tity from 2i5,634,925,i33,82o 9 , we get 2i5,634,76o,89O,4i6,62O 9 cubic miles as the volume to which the nebula had been reduced by the separation of the ring. 94 New Theories in Astronomy. For the dimensions of the ring we have the mean diameter of the orbit of the representative Asteroid as 520,600,000 miles, that is twice its distance from the centre of the nebula, which makes its circumference to be 1,635,516,960 miles in length. Dividing then the volume of the ring, which we found to have been i64,482,/i7,2OO 9 cubic miles by this length, the area of its cross-section must have been 100,569,251,938 square miles, which divided by the breadth of 171,000,000 miles the differ- ence between the radii of the Asteroidal and Martian nebula, namely 372,000,000 less 201,000,000 makes the thickness of the ring to have been 588 miles. But the inner having been ^ '339 times more than the outer edge, as we shall see presently, the average thickness would be 185 miles. MARTIAN NEBULA. The volume of the last nebula after the separation of the ring for the Asteroids was found to have been 2 1 5,634,760,890,41 6,62O 9 cubic miles, which had to be con- densed into the volume of the Martian nebula of 402,000,000 miles in diameter, which would give a volume of 34,01 5, 582,677,165, 354 9 cubic miles. Dividing then, the larger of these volumes by the smaller, we find that the density of the Martian nebula had been increased 6*339 times by the condensation. But we found the density of the Asteroidal nebula to have been 447,218,905 times less dense than water, dividing which by 6*339 makes the Martian nebula to have been 70,547,110 times less dense than water. This divided again by 773*395 makes it 91,259 times less dense than air, and consequently its absolute temperature to have been 0*00300243 or -273-99699757. From the Martian nebula of 402,000,000 miles in diameter, volume 34,01 5, 582,677, 165, 354 9 cubic miles, and density 70,547,110 times less than water, we have to deduct the volume of his ring, which by Table II., was estimated at 160,728,460,000 cubic miles at density of water. Multiplying this by 70,547,110 we find its volume to be 11, 338,927, 154 9 cubic miles at the same density as the nebula, deducting New Theories in Astronomy. 95 which from its whole volume we get 34,015, 571, 338,237,2OO 9 cubic miles as the volume after the separation of the ring. For finding the dimensions of the ring we have 283,300,000 miles as the mean diameter of the orbit of Mars, which makes its circumference 890,015,280 miles in length. Then dividing the volume of the ring 1 1,338,927,1 54 9 cubic miles by this length, the area of its cross-section comes to be 12,740,148,859 square miles, which, divided by the breadth of 83,690,000 miles that is one-half of the difference between the diameters of the Martian and Earth nebula, respectively 402,000,000 and 234,620,000 miles makes the thickness of the ring to have been 152 miles. But as before, the inner having become through condensation, 5-0302 times more dense than the outer edge, the average thickness would be 61 miles. EARTH NEBULA. As the volume of the nebula was 34,oi5,57i,338,237,2OO 9 cubic miles after the separation of the ring for Mars, we have to condense it into the volume of the ear.th nebula, which at 234,620,000 miles in diameter would be 6,762,303,076,923,03 1 9 cubic miles. Dividing the larger of these volumes by the smaller we find that the density of the nebula has been in- creased 5 '0302 times, as employed above. But we found the density of the Martian nebula to have been 70,547,110 times less than that of water, dividing which by 5*0302 makes the earth nebula to have been 14,024,781 times less dense than water. Dividing this again by 773*395 we find it to have been 18,134 times less dense than air, and 274 divided by this density of air the same as in all the respective cases gives O' 015 1097 as the absolute temperature of the nebula and corresponds to -273 9848903. From the earth nebula 234,620,000 miles in diameter, 6,762,303,076,923,03 1 9 cubic miles in volume, and 14,024781 times less dense than water, we have to subtract the volume of the ring of the earth's system, which, in Table II., appears as 1,489,310,236,000 cubic miles at density of water. Multi- ply ing this by 14,024,781 we fin ditto have been 20,887,249,553 96 New Theories in Astronomy. cubic miles at the same density as the nebula. And sub- tracting- this quantity from 6,762,303,076.923,03 1 9 , we get 6,762, 282, 189,673, 478 9 cubic miles for the volume of the pre- vious nebula after the separation of the ring for the system of the earth. For finding the dimensions of the ring we have 185.930,000 miles for the mean diameter of the Earth's orbit, which makes the circumference 584,117,688 miles in length, and dividing the volume of the ring for the system, which was found to be 20,887,249, 5 S3 9 cubic miles, by this length, the area of its cross section comes to be 3 5,760,344, 109 square miles, which divided by the breadth of 37,205,000 miles that is one-half of the difference between the diameters of the Earth and Venus nebulae, respectively 234,620,000 and 160,210,000 miles makes the thickness of the ring to have been 961 miles. But the inner will presently be seen to have been 3*141 times more dense than the outer edge when its separation was com- pleted, so that the average thickness would be 612 miles. VENUS NEBULA. As the volume of the nebula was 6,762, 282, i89,673,47S 9 cubic miles after the separation of the ring for the system of the Earth, we have to condense it into the volume of the Venus nebula, which at 160,210,000 miles in diameter would be 2,i53,i2O,792,O79,2o8 8 cubic miles. Then dividing the larger of these two volumes by the smaller, we find that the density of the Venus nebula had been increased to 3' 141 times what that of the Earth nebula was. But we found the density of that nebula to have been 14,024,781 times less than that of water, dividing which by 3*141 makes the Venus nebula to have been 4,465,512 times less dense than water. Dividing this again by 773*395 we find it to have been 5,774 times less dense than air, which would make its absolute temperature to have been O' 04745486, which corresponds to 273 '9525459. From the Venus nebula of 160,210,000 miles in diameter, volume 2, 1 5 3, 1 20,792,079,207,92 1 6 cubic miles, and density 4,465,512 times less than that of water, we have now to New Theories in Astronomy. 97 deduct the volume of her ring, which by Table II. is 1, 1 3 1, 960,000,000 cubic miles at the density of water. Multi- plying this volume by 4,465,512 we find the volume of the ring to have been 5,054,780, 604,65 1 6 cubic miles at the same density as the nebula, and subtracting this amount from 2,i53,i20,792,079,207,92i 6 we get 2 153,1 i5,737 2 98,6o3 6 cubic miles for the volume to be condensed into the nebula following. To find the dimensions of the ring we have 134,490,000 miles for the diameter of the orbit of Venus, which makes its circumference 422,513,784 miles in length. Then dividing the volume of the ring, i.e. 5,054,780,604,65 1 6 cubic miles by this length, the area of its cross-section comes to be 11,963,821,788 square miles, which, divided by the breadth of 28,489,000 miles that is one-half of the difference between the diameters of the Venus and Mercurian nebulae, respectively 160,210,000 and 103,232,000 miles makes the thickness of the ring to have been 420 miles. But the inner edge having become, in the process of separation, 3*738 times more dense than the outer one (see below) the average thickness would be reduced to 225 miles. MERCURIAN NEBULA. As the volume of the nebula was 2,1 53,1 15,7 37,298,6o3,27o 6 cubic miles after the separation of the ring for Venus, we have to condense it into the volume of the Mercurian nebula, which at 103,232,000 miles in diameter would be 576,026,613, 333, 333, 333 6 cubic miles. Then, dividing the larger of these two volumes by the smaller, we find that the density of the Mercurian nebula must have been increased 3*738 fold over that of its predecessor. But we find the density of the Venus nebula to have been 4,465 512 times less than water, dividing which by 3*738 makes the Mercurian nebula to have been 1,194,666 times less dense than water. Dividing again this density by 773 395 we find it to have been 1545 times less than air, and 274 divided by this air density gives o* 1773463 as its absolute temperature, which corresponds to -273-8226537. H 98 New Theories in Astronomy. From the Mercurian nebula 103,232,000 miles in diameter, volume of 576,026,61 3, 333, 333, 333 6 cubic miles, and density of 1,194,666 times less than water, we have to deduct the volume of his ring, which by Table II. is 92,735,000,000 cubic miles at density of water. Multiplying this volume by 1,194,666 makes the ring to have been I io,787,355,3OO 6 cubic miles in volume at the density of the nebula, and sub- tracting this amount from 576,026,61 3,333,333,3336, we get 576,026,502,545 978,O33 6 cubic miles for the volume to be condensed into the nebula following. To find the dimensions of the ring we have 71,974,000 miles for the mean diameter of the orbit of Mercury, which makes its circumference 226,1 13^1 8 miles in length. Then dividing the volume of his ring, i.e. 1 10,787,355, 3OO 6 cubic miles, as above, by this length, the area of its cross-section comes to be 489,963,459 square miles. Here we have to determine the breadth of the ring in a new way, that is em- pirically. Seeing that the breadth of the ring for the earth's system was 37,205,000 and of that for Venus 28,489,000 miles, we shall assume 20,000,000 miks for the breadth of the ring for Mercury. This will make the residuary, now the Solar nebula, to have been 31,616,000' miles in radius and 63,232,000 miles in diameter. Returning now to the area of the cross-section of the ring, that is, 489 963,459 square miles, and dividing it by the assumed breadth 20,000,000 miles, makes the thickness of the ring to have been 25 miles. But, as before, its inner edge having become 4*354 times more dense than the outer one during the process of separation (see below) the average thickness must have been only 1 1 miles. SOLAR NEBULA. Lastly, as the volume of the nebula was 576,026,502,545 978,033 6 cubic miles after the separation of the ring for Mercury, we have to condense it into the volume of the Solar nebula, which at 63 232,000 miles in diameter would be 132376310,975609,756' New Theories in Astronomy. 99 cubic miles. Then dividing the first of these two volumes by the second, we find that its density must have been increased 4-3514 fold. But we found that the density of the Mercurian nebula was 1,194,656 times less than that of water, dividing which by 4*3514 makes the Solar nebula to have been 274,546 times less dense than water. Dividing this in turn by 773*395 shows it to have been 355 times less dense than air, and, still further, dividing 274 by this air density makes its absolute temperature to have been 0*7718585 equal to -273 2281415. We might conclude our analysis here, but it will be more convenient to carry our calculations a few steps further, to save the additional trouble that might be occasioned by having to return to them later on. First we shall condense the Solar nebula to 211,911 times less dense than water, and therefore 274 times less dense than air, which we may note will increase its density 1*2956 times. This supposed to be done, its diameter would be 58,002 920 miles, its volume 1 02, 176,1 29,4 12 12 cubic miles, and its density sf^th of an atmosphere about one-ninth inch of mercury which would, in consequence, make its absolute mean heat equal to one degree of the ordinary Centigrade scale, or, in another way of expressing it, equal to 273. Second. Let us condense this same nebula to 773*395 times less dense than water, and consequently to the density of air at atmospheric pressure, then its diameter will be 8,930,309 miles, volume 372,905, 56o,345 9 cubic miles, and the mean heat o, or the heat of freezing water which by some unexplained process of thought has hitherto been considered to be 274 of absolute temperature. Third. By again condensing the Solar nebula to the density of water, corresponding to a pressure of more than 773 atmospheres, its diameter becomes 972,285 miles, its volume 482, i67 12 cubic miles, and mean heat 775, including the 2 C acquired in condensing it to the pressure of I atmosphere, as is plainly shown in Table III. Before going any further we must enter into a digression to examine into the process of thought by which the absolute H 2 TOO New Theories in Astronomy. zero of heat has come to be called the absolute zero of temperature, and absolute temperature to be so many degrees of negative less than o or nothing heat counted from the lower or wrong end, to be called positive absolute temperature ; thus making heat and temperature appear to be two very different things, without giving any explanation of what is the difference between them. Science has, as it were, gone down a stair of 274 steps carrying along with it the laws of gases, and has found, most legitimately, with their assistance the total absence of even negative heat at the bottom of it ; and, leaving these laws there, has jumped up to the top of the stair, thinking that it carried along with it 274 of absolute heat, which it now calls temperature ; instead of bringing the said laws up with it and verifying, if not at every step at least at intervals, how much it brought up with it of what it had taken down. Had it done so it would have found that at the top of the stair it had got what was equal to only 2 of positive heat as measured by the Centigrade scale, as has been shown above, which might be called temperature, but that would not mend matters. Science seems to have forgotten, for the time being at least, all about the laws of gases ; it had got something which it thought would enable it to mount much higher, and was satisfied. It will not be difficult to do away with the con- fusion of thought that is thus shown to have occurred. The laws of gases are founded upon the fact that in gases there is a necessary interdependence between heat and pressure, and the starting points adopted by science for calculating this interdependence in them are o of heat and I atmosphere of pressure at o of heat. Obeying these laws, we have argued, from the beginning of our operations, that heat requires something to hold it in, and that the nebula from which the Solar system was formed if it was so formed could only contain heat in proportion to its density ; that is being a gas, or vapour in the form of a gas, it could not con- tain, i.e. hold in it, more than 2 of positive heat when its density was equal to the pressure belonging to I atmosphere of a gas ; all as shown in the most irrefragable manner in this chapter and in the accompanying Table III. New Theories in Astronomy. 101 A gas can be easily compressed in a close vessel to a pressure of 100 atmospheres, which would enable it to hold 1 00 of heat due to that compression ; in fact, were it compressed to that degree by a piston in a cylinder, without any loss of heat, it would be raised to that heat by that act alone, but that would raise it to only 102 instead of 374 of what is called absolute temperature according to present usage ; because as a gas it could not hold any more heat at that pressure. It is, therefore, evident that this usage has not been derived from the laws of gases. Neither has it been derived from the other two states of liquid and solid to which all gases can be reduced, as can be ver,y easily demonstrated. To cool steam at atmospheric pressure from its gaseous to its liquid state 519 of heat of one kind and another as measured by the Centigrade thermometer have to be ab- stracted from it, which leaves the liquid at its boiling point of 1 00 a quantity that has been arbitrarily adopted to mark the difference between the freezing and boiling points of this liquid. In order, after this, to reduce the liquid, now water, to the freezing, or what is called o of heat, these 100 degrees of heat have to be extracted from it, which is not very difficult to do because the heat put into it arbitrarily can be extracted from it ; but if it is now wanted to change the steam from its liquid to its solid state, the work, or operation assumes a very different character, because heat cannot be extracted from a substance which contains none at all. It is well known that 80 of heat are required to change one pound of ice at o into a pound of water also at o of heat ; but it is equally well known that 80 of heat cannot be taken out of the pound of water which has none in it ; how then, is the water to be changed into ice ? Even in cooling water to o it has to be put into a bath of some kind, either of cold water or some cold mixture of other substances at least as cold ; because, otherwise, extrane- ous heat from any source might find its way into it, and prevent it from cooling down to zero of heat. In the same manner, to change the water into its solid state of ice it has to be put into a similar bath, not to extract heat from it, because it has not any to extract, but to prevent extraneous heat from iO2 New Theories in Astronomy. getting into it. This being the case, it is evident that if water is put into a bath at what is called - i of heat, or even a frac- tion of that amount, it will be converted into ice though very gradually, by keeping extraneous heat from getting to it to sustain the collisions, or vibrations, of its constituent atoms necessary to maintain it in its liquid state. All for the very same reason why a stone, a piece of metal, or of anything assumes the same degree of heat, or absence of heat, as the medium by which it is surrounded ; be it derived from sun- heat, earth-heat, or heat produced chemically or mechanically, and is not cooled down to a lower degree than the surround- ing bath, be it what it may. The heat required to change a solid into a liquid is called latent /teat, which in the case of ice and water may be a frac- tion of 1 or" 80, or minus almost anything according to the time it is necessary for it to act ; so that no quantity of what is called absolute temperature can be ascribed to ice without the element time being involved in it. The absolute temper- ature of water and ice, just changing from freezing to frozen, might be counted as the same, seeing that a fraction of a degree of heat may make all the difference between them ; but no fixed absolute temperature can be applied to ice, as it, in conjunction with all solid bodies, may have any degree of absolute temperature between its melting point and the abso- lute zero of heat, as far as is at present known. The same, of course, must be the case with any gas or vapour, or nebulous matter changed into its liquid and then solid state ; and this fact enables us to go a little further. We have seen that what, according to present usage, is called the absolute temperature of solid hydrogen may be anything between -257 and 274 of heat, that is, between the absolute temperature of o and 17, which, of course, is no measure at all ; and, therefore, absolute temperature can only be looked upon as a conventional term, which, when added to positive Centigrade, or other, heat, conveys no clear idea to the mind, as it must always be mixed up with the concomitant idea of latent heat and its time of action. This leads us to think of what remains in the vessel, in which pure hydrogen New Theories in Astronomy. 103 has been changed into its liquid and then solid state, after these operations have been performed ; and our first conclusion comes to be that there can be nothing in it but a small piece of solid hydrogen ; but from the limited accounts we have seen of these operations, there does appear to be something remaining, because it seems that by it the degree of negative heat in the vessel can be measured. What that remaining something may be can hardly be anything but a matter of conjecture. The first and most probable idea that occurs is that it may be some lighter gas mixed with the pure (?) hydrogen that was put into the vessel ; the next is that it may be the vapour of solid hydrogen ; and the last refuge for speculation is that it may be radiant matter, whatever that may turn out to be. At one time it was supposed to be im- purities mixed with the gases operated upon, which in the case of common, air, were found to be removed to a certain extent by means of absorbents ; but the numerous com- ponents of common air discovered since that time, have gone far to throw light upon that supposition, and we are thus led to think of what a true gas really is. But we are not yet prepared to follow up this thought. This is not an inappropriate place to say that when we adopted the Centigrade scale for our work, we thought that a special thermometer, decimal throughout and consequently more handy, might be arranged for science alone, leaving every man the free use of whatever scale he liked best ; but our experience acquired in this chapter put an end to that thought, and has left us totally unable to see how any decimal scale can be contrived, which will start from absolute zero of heat and will admit of any combination with any existing scale, or will assist humanity in any of its operations in con- nection with heat and temperature, whichever science may choose to call it. We therefore see that no known thermo- meter scale is superior to another, and end where we began by saying that the Centigrade is the fashionable one at the present time. It is decimal as far as boiling water and result- ing steam are concerned, but all the world is not boiling water ; even steam has to be complicated with latent heat. TABLE III. ABSTRACT OF MEASUREMENTS, ETC., RESULTING Nebulae. Explanations. Volume of the Mass of each Separate System at Density of Water in cubic miles. Times less D^nse than Water. Increase of Density in times. Name. Diameter in miles. Original or ) Neptun an } Ditto . . 6,600,000,000 Volume of Neptune's Ring . 29 , 107 , 964 , 680 , 925 311,754,100,720 311,754,100,720 Ditto . . M Volume of Nebula less ring . .. Uranian . 4,580,000,000 Condensed from Neptunian Nebula .. .. 2-9923 Ditto . . .. Volume of Uranus' Ring . . 25,876,388,977,000 104,184,535,721 .. Ditto . . " Volume of Nebula less ring . . " Saturnian . 2,672 ( OOO,OOO Condensed from Uranian Nebula . .. .. 5 '357 Ditto . . .. Volume of Saturn's Ring 1 5437>7347743i5 20,689,000,000 .. Ditto . . Volume of Nebula less ring . . .. - Jovian . . 1,370,800,000 Condensed from Saturnian Nebula . .. .. 7*4037 Ditto . . .. Volume of Jupiter's Ring . 479.368,921,317,000 2 >794. 4 I 74 20 .. Ditto . . " Volume of Nebula less ring . .. Asteroidal . 744,000,000 Condensed from Jovian Nebula .. .. 6-2484 Ditto . . .. Volume of Asteroidal Ring . 367,792,000,000 447,218,905 .. Ditto . . Volume of Nebula less ring . .. " - Martian 402,000,000 Condensed from Asteroidal Nebula . .. .. 6-3392 Ditto . . .. Volume of Martian Ring 160,728,460,000 70,547,110 .. Ditto *. . Volume of Nebula less ring . .. Earth . . 234,620,000 Condensed from Martian Nebula . .. .. 5*0302 Ditto . . .. Volume of Earth Ring . . 1,489,310,236,000 14,024,781 .. Ditto . . " Volume of Nebula less ring .. - " Venus .' l6o,2IO,000 Condensed from Earth Nebula . .. .. 3-1410 Ditto . . .. Volume of Venus Ring ... 1,131,960,000,000 4,465,512 .. Ditto . . " Volume of Nebula less ring . . .. - Mercurian . 103,232,000 Condensed from Venus Nebula .. .. 3' 7 379 Ditto . . .. Volume of Mercurian Ring . . 92,735,000,000 1,194,666 Ditto . . - Volume of Nebula less ring * . .. Solar . . 63,232,000 Condensed from Mercurian Nebula. .. 274.S4 6 4'35 J 4 Ditto . . 58,002,920 Volume at -^ of an atmosphere .. 211,911 i '2956 Ditto . . 8,930,309 Volume at density of one atmosphere .. .. 274-000 Ditto . . 972.895 Volume at density of water . . .. - 773 '395 *OM THE CALCULATIONS MADE IN CHAPTER V. Volumes at Densities of Respective Nebulae in cubic miles. Times less Ue'ise than Air. Absolute Tempera- ture. (Degrees.) At Density of Water. At Air Density. Dimensions of Rings. Space to Grain of Matter. Inches Breadth in miles. Thick- ness in miles. Aver- age Thick- ness in miles Cubic Feet. Side of Cube in Feet. 150,532,847,222,000, ooo , ooo , ooo , ooo , ooo 403,000,000 o" 00000068 .. .. . . 7i3 22 3 89*327 9,074,530,000,000,000,000,000,000 1,010,000,000 5H.794 341,196 150,523,772,692,000,000,000,000,000,000 50,303,255,814,000,000,000,000,000,000 2,695,918,851,000,000,000,000,000 134,710 620 0*00000203^ 954,000,000 252,193 100,553 238,357 61*994 50,300,559,895,149,000,000,000,000,000 9,988,700,000,000,000,000,000,000,000 3,193,775,478,000,000,000,000,000 26,750,876 O'OOOOIO24 650,600,000 881,037 238,000 47.313 36-168 9,985,506,224,522,000,000,000,000,000 1,348,720,186,335,000,000,000,000,000 I >339>557' I 5S' OOO ' OOO ' OOO ' OOO > O00 3,613,182 0*00007583 313,400,000 1,406,771 450,282 6,303 18*472 1,347,380,629,180,000,000,000,000,000 i 215, 634, 925, 373, 133, 820, ooo, ooo, ooo 164,482 .717,200,000,000,000 578,254 0*00047384 171,000,000 588 185 1,023 10*075 215,634,760,890,416,620,000,000,000 34,015,582,677,165,354,000,000,000 11,338,927,154,000,000,000 9 I > 2 59 0*00300244 83,690,000 152 61 161 5 '445 34,015,571,338,237,200,000,000,000 6,762,303,076,923,031,000,000,000 20,887,249,553,000,000,000 18,134 0*0151097 37,205,000 961 612 3 2 3-I78 6,762,282,189,673,478,000,000,000 2,153,120,792,079,207,921,000,000 5,054,780,604,651,000,000 5774 *47454 28,489,000 420 225 I0'2 2*170 2,153,115,737,298,603,270,000,000 576,026,613,333,333,333,000,000 110,787,355,300,000,000 1.545 0*1773463 20,000,000 25 ii 2 '734 1-398 576,026,502,545,978,033,000,000 132,376,310,975,609,756,000,000 355 0*771831 .. .. .. 0*6283 0-8565 10*28 102,176,129,412,000,000,000,000 274 0*99635 .. .. .. 0*4848 0*7856 9'43 372,905,560,345,000,000,000 o 2*0000 * * 0*00177 O"I2I i'452 io6 New J^heories in Astronomy. Returning now to page 84, we see that the volume of the sun alone was considered to be 482, i6g 12 cubic miles, which corresponds to a diameter of 972,869 miles. Comparing this with the volume 482, i6/ 12 cubic miles, see page 99, left after all the members of the Solar system have been separated from the original nebula, we find that there is a remainder of 2,000,000,000,000 cubic miles less than we ought to have. But it will be remembered that we added only T^jo tn part to the mass of the sun for the mass of the whole Solar system, whereas it will be seen, by referring to Table I L, that we ought to have added g-ggr^gth part. Had we done so the sphere containing the whole Solar system at the density of water would have been 973,361*31 miles in diameter with volume of 482,860,744** cubic miles, which would have added 3,153,681,000,000 cubic miles to the volume we started with, and would have left us with 1,375.903,430,000 cubic miles more than we ought to have had. Besides, for the sake of round numbers, we made the diameter of the nebula containing the whole Solar system, at the density of water, to be 973,360 instead of 973, 359' 208 miles, and thereby really added more to the original volume than we should have ; so that the defects in accuracy at the beginning of our work partially counterbalanced each other, which accounts so far for the difference noted at the end not being much more than half of what it should have been. Taking all this into considera- tion, and the really insignificant magnitudes of the differences that would result from the corrections that could be made, we have not thought it necessary to reform the whole of our calculations. Besides, the data we have been working upon are not so absolutely exact as to insure us that we should get nearer to the truth by making the revision. The whole error would be much more than obliterated were we to apply 5 67 instead of 5 '66 for the mean density of the earth to the debit side of the sun's account. To simply describe arithmetical operations conveys no really satisfactory meaning to the mind ; of working them out in full there is no end ; and to partially represent them as we have done in these pages, although showing how the results New Theories in Astronomy. 107 are arrived at, still leaves them so mixed up together that it is difficult to compare them with each other, and to note the sequences from the beginning to the end of the whole opera- tion. For these reasons we have compiled Table III., where the whole of the principal and most important data, and results from them, may be followed out and examined. We may now say that we have taken our nebula to pieces, with the exception of the parts belonging to the satellites of those planets which have them ; which would only be a tiresome repetition of what we have done for each principal member of the system, provided we had the necessary data, which we have not ; and have thus acquired a certain amount of knowledge of the primitive conditions of each one of them. But we have still to examine into and draw conclusions from what we have seen and learned during the operation ; which in some points, differ very much from our notions, formed from what we had previously read on the subject. io8 New 77ieories in Astronomy. CHAPTER VI. PAGE 1 08 Analysis continued. Excessive heat of nebula involved condensa- tion only at the surface. Proof that this was Laplace's idea. 109 Noteworthy that some astronomers still believe in excessive heat. 1 10 Interdependence of temperature and pressure in gases and vapours. Collisions of atoms the source of heat. no Conditions on which a nebula can be incandescent. Sir Robert Ball. 112 No proper explanation yet given of incandescent or glowing gas. 115 How matter was thrown off, or abandoned by the Jovian nebula. 116 Division into rings of matter thrown off determined during contrac- tion. 117 How direct rotary motion was determined by friction and collisions of particles. 118 Saturn's rings going through the same process. Left to show process. 1 20 Form gradually assumed by nebulae. Cause of Saturn's square- shouldered appearance. 1 20 A lens-shaped nebula could not be formed by surface condensation. 121 Retrograde rotary motion of Neptune and Uranus, and revolution of their satellites recognised by Laplace as possible. 123 Satellites of Mars. Rapid revolution of inner one may be accounted for. 124 Laplace's proportion of 4000 millions not reduced but enormously increased by discoveries of this century. ANALYSIS OF THE NEBULAR HYPOTHESIS continued. WHEN Laplace elaborated his hypothesis, heat was considered to be an imponderable material substance, and continued to be thought of as such though perhaps not altogether believed to be so for somewhere about half a century afterwards ; so that it cannot be wondered at that he thought the nebula could have been endowed with excessive heat, more especially as it was looked upon as imponderable, and could in no way have any effect on the mass of the nebula. He only accepted the idea that was common to almost all astronomers of his time, that nebulae were masses of cosmic matter of extreme New Theories in Astronomy. 109 tenuity but self-luminous, and consequently possessed of intense heat ; they saw the sun gave light and felt its heat, and very naturally thought the nebula must be hot also. Without this idea he could not have formed the hypothesis at all, because he could not have conceived that the condensa- tion of the nebula could only take place at its surface, or, as he terms it, " in the atmosphere of the sun," as most assuredly would be the case with an excessively hot body. And in order that there may be no doubt about this being his idea, we quote his own words as guaranteed by M. Faye in " L'Origine du Monde " : " La consideration des mouvements planetaires nous conduit done a penser qu'en vertu d'une chaleur ex- cessive I'atmosphere du soleil s'est primitivement etendu au dela des orbes de toutes les planetes, et qu'elle s'est reserree successivement jusqu'a ses limites actuelles." And again : "Mais comment 1' atmosphere solaire a-t-elle determine les mouvements de rotation et de revolution des planetes et des satellites ? Si ces corps avaient penetre" profondement dans cette atmosphere, sa resistance les aurait fait tomber sur le soleil. On peut done conjecturer que les planetes ont ete formees a ses limites successives par la condensation des zones de vapeurs qu'elle a du, en se refroidissant, abandonner dans le plan de son dquateur." Proceeding on these ideas Laplace was quite in order and logical in conceiving that successive rings could be abandoned by the hot nebula, through the centrifugal force of rotation, for the formation of planets, more or less just in the way we have separated them. Having obtained his end quite legitimately, as he thought, in this way, he had no occasion to look any deeper into the affair, and consequently was not under the necessity of taking any thought of what the interior construction of the nebula might be, any more than so many others have not done since his day. That he should have conceived the nebula to have been endowed with intense heat was, as we have already said, a natural consequence of the mistaken notions of the nature of heat at that period ; but that so many astronomers should, up to the present day, think that the nebula must have been no New Theories in Astronomy. intensely hot, even to the degree required to dissociate the meteorites of which they conceive it to have consisted, seems to us to be almost inconceivable. We believe we have shown abundantly plainly, that there could have been almost no heat in the primitive nebula, because there was hardly any cosmic matter to hold it in. We have given as proof of this the laws of gases recognised and accepted by every scientist, according to which a gas cannot contain a stated amount of heat except it be at a pressure corresponding to that temperature, that is unless it is subjected to conditions foreign to its natural state. Therefore we must either persist in maintaining that there was almost no heat in the original nebula, or we must throw the laws of gases to the winds, for they all depend one upon another. There may be nebulae possessed of very high tem- perature, that of incandescence for example, but certainly the nebula out of which the solar system was made, could not have contained more heat than what we have shown it had at the various stages through which we have carried it. If there be nebulae at the temperature of incandescence, they must be possessed of densities, or pressures, corresponding to that temperature. A few pages back we have spoken of the impossibility of two grains of matter 90 feet apart, raising, by mutual collisions, their temperature and that of the space occupied by each to the temperature of incandescence, and if we now substitute for them meteorites of a pound weight each, the space occupied by each of them will be a cube of 1670 feet to the side, which does not help us in any way to believe that the spaces occupied by them could be heated up by their collisions, so as to shine with the temperature of incandescence. So we get no help from meteorites. Some people evidently seem to think that nebulse can be incandescent and give the spectrum of incandescent gas, with- out their density or pressure being increased to the corre- sponding degree. Sir Robert Ball seems to be one of them, though at the same time he appears to be not altogether sure of it. When discussing the self-luminosity of the nebula in Orion, in his " Story of the Heavens," Ed. 1890, p. 465, he says: "We have, fortunately, one or two very interesting New ^Fheories in Astronomy. 1 1 1 observations on this point. On a particularly fine night, when the speculum of the great six-foot telescope of Parsonstown was in its finest order, the skilled eye of the late Earl of Rosse and of his assistant, Mr. Stoney, detected in the densest part of the nebula myriads of minute stars, which had never before been recognised by human eye. Unquestionably the com- mingled rays of these stars contribute not a little to the brilliancy of the nebula, but there still remains the question as to whether the entire luminosity of the great nebula can be explained, or whether the light thereof may not partly arise from some other source. The question is one which must necessarily be forced on the attention of any observer who has ever enjoyed the privilege of viewing the great nebula through a telescope of power really adequate to render justice to its beauty. It seems impossible to believe that the bluish light of such delicately graduated shades has really arisen merely from stellar points. The object is so soft and so continuous might we not almost say ghost-like ? that it is impossible not to believe that we are really looking at some gaseous matter." Here we see that his own belief about the matter is not very firm. He admits that the stars contribute not a little to the brilliancy of the nebula, and the most he can say in favour of its shining with its own light is, that it seems im- possible to believe that the light has arisen merely from stellar points. He then goes on to show how the self-luminosity may be explained, as follows : " But here a difficulty may be suggested. The nebula is a luminous body, but ordinary gas is invisible. We do not see the gases which surround us and form the atmosphere in which we live. How, then, if the nebula consisted merely of gaseous matter, would we see it shining on the far distant heavens? A well-known experiment will at once explain this difficulty. We take a tube containing a very small quan- tity of some gas : for example hydrogen ; this gas is usually invisible ; no one could tell that there is any gas in the tube, or still less could the kind of gas be known ; but pour a stream of electricity through the tube, and instantly the gas 1 1 2 New Theories in Astronomy. begins to glow with a violet light. What has the electricity done for us in this experiment ? Its sole effect has been to heat the gas. It is, indeed, merely a convenient means of heating the gas and making it glow. It is not the electricity which we see, it is rather the gas heated by the electricity. We infer, then, that if the gas be heated it becomes luminous. The gas does not burn in the ordinary sense of the word ; no chemical change has taken place. The tube contains exactly the same amount of hydrogen after the experiment that it did before. It glows with the heat just as red-hot iron glows. If, then, we could believe that in the great nebula of Orion there were vast volumes of rarefied gas in the same physical condition as the gas in the tube while the electricity was passing, then we should expect to find that this gas would actually glow." There is a great deal to be said about this explanation. We presume that a very small quantity of hydrogen gas means that it was considerably below atmospheric pressure. Even so we admit that by introducing sufficient heat into the tube by means of electricity or otherwise, the gas could be raised to the temperature of incandescence, but its pressure would, at the same time, be increased to the corresponding force measured in atmospheres ; and we also admit that when the gas was allowed to cool down to its original temperature, the same quantity of hydrogen would be found in the tube ; but how about the tube ? When the gas came to be at the temperature of incandescence the tube would be the same, or very soon raised to it, and being made of glass would be sufficiently plastic to be distorted, or even burst by the pres- sure within, probably even before the gas reached the tempera- ture of incandescence. We must not forget that the first appearance of incandescence begins with red heat whose temperature is not far from 500 in daylight, and that white heat rises to above 1000. If the experiment was made in an almost capillary tube, sufficiently thick to prevent accidents, then it might appear to prove a foregone conclusion, but nothing else ; it might keep the idea of pressure out of sight, but it could not prove that the gas inside was in a rarefied state when incandescent. That the gas glowed the same as a New Theories in Astronomy. \ \ 3 red-hot bar of iron has not been shown. The gas had to be shut up in a tube to make it glow, but the bar of iron could glow outside of the tube. Could a streak of hydrogen be put into a furnace along with a bar of iron and heated to in- candescence by its side, there might be some fair comparison between them, as long as they were in the furnace together, but the moment they were taken out the glow would disappear from the gas, whereas the iron would glow for some time. On the other hand we might say that a stream of incandescent gas might be made to heat a bar of iron in an oven to its own temperature, but the moment the stream of gas and the iron bar were removed from the oven, the former would disappear at once and the latter would continue to glow, simply because it was dense enough to contain a very considerable supply of heat compared to what the gas could, or rather, because the pressure of the gas, even did it correspond to the temperature, would disappear at once and the heat with it. So it is not always safe to say things. But it is quite safe to say that no gas or substance such as we are accustomed to look upon as gas can abide in a state of incandescence, and merely glow, unless its pressure, or density, corresponds to the temperature of incandescence ; which for red heat (in the dark) would be 370 = 2 '35 atmospheres, and for white heat at 1000= 4*65 atmospheres, above absolute zero of pressure in both cases. And also, that if the self-luminosity of a nebula arises from incandescent gas, the pressure in the gas of that nebula must be somewhere between 2 and 5 atmospheres above absolute zero of pressure. Now we have shown, at page 85, that the density and pressure in the solar nebula, at the stage there specified, could not have been more than the 403 millionth part of those of our atmosphere, and consequently were justi- fied in asserting that in it there could be almost no heat whatever. We have just been speaking of a streak of gas and a bar of iron being heated in an oven to a red or white heat side by side, but everybody knows that this could not be done ; but everybody has not thought of why it could not be done, otherwise Sir Robert Ball would not have favoured us with H4 New Theories in Astronomy. his laboratory experiment of a streak, or remnant, of hydrogen in a glass tube. We know that a plate, or bar, of iron can be heated up to the temperature of incandescence in an oven, but it has never occurred to anyone, who has seen the thing done, that the gas, air, or vapour which heats them must be at a pressure corresponding to that temperature. Multitudes of people may have thought of how the thing is done, but apparently very few have thought that it is not the gaseous part of the current of heated matter introduced into the oven, that heats it and the metal in it, but the solid part which is the distinctive and most important part of the constituents of the current. The solid part of the matter let it be gas or any other element is heated to incandescence in some furnace and carried along by the gaseous part that is the stuff that fills the empty spaces between the solid molecules to give it out to the oven and iron. We are not sure that the gaseous part even glows. We see plainly enough that the walls of the oven glow, but with respect to the gas, or carrying agent, we are inclined to think that it rather dims the glow of the oven and iron than otherwise. In passing, we say it is not unreasonable to suppose that the solid matter which contained the heat till it was given out, consisted of the elements which were put into the furnace to raise the heat, and of those which were drawn in by the draught in a word, the elements of combustion but about the carrying constituent there is a great deal to be said after we know more about it. It seems to us from all this that the hydrogen gas in Sir Robert Ball's tube was not made to glow by heating up to the temperature of incandescence, but somehow by the electricity passing through it, if it did pass. We, therefore, come to the conclu- sion that the light of nebulae does not come from gas or what we call gas heated up to be incandescent merely to make it glow, and that it might be as cold as the light that comes from the aurora, or as that of a glowworm. Sir Robert Ball refers to stellar points seen through the nebula, and acknowledges that part of the glow may be due to them, which shows that the nebula must have been excessively tenuous ; for we know how thin a cloud will hide Sirius from us, New Theories in Astronomy. 115 and we think that nobody will assert that two grains of matter dispersed in 1, 4.26,44 5 cubic feet of space, as we have seen at page 86, would hide Sirius from us. Therefore, we must acknowledge that the glow of nebula in Orion, observed by Sir Robert Ball, was caused either by the stellar points, or by some other thing that most assuredly could not be gas heated to the temperature of incandescence, or in part from both. For we believe that the glowing of nebulae, fluorescence, phos- phorescence, Will-o'-the-wisp, auroras, fire-flies, fire-on-the- wave, etc., etc., all, all proceed from the same cause. We may now proceed to say a few words about the separation of the rings for the planets, brought about by the rotation of the nebula on its axis, and the centrifugal force produced throughout it thereby. We have shown, at page 88, that a ring could not be detached from the nebula at once in one large annular mass, as it seems to have been the common notion was the mode of separation ; and we shall now try to show with some detail what the process must have been, notwithstanding that it has been in a general way described by others ; because, like everything else, there is something to be learnt from it. For this purpose we shall select what we have called the Jovian nebula, because we can suppose, for the present, it must have been more nearly in the form of a sphere than either the original or any of the exterior nebulae, which may not have been properly licked into shape, as it were ; and also because we have found that the thickness and mass of the ring for his, Jupiter's, system were vastly greater than those for any other one of the planets. We have made the Jovian nebula to have been 1,370,800,000 miles in diameter, and the greatest thickness of the ring detatched from it to have been 1,406,771 miles. Now in a circle of that diameter, a chord of the length of that thickness would subtend an arc of very little more than 7 minutes, one half of which we shall suppose to be measured on each side of the equatorial diameter of the nebula at right angles to the diameter ; then, the middle ordinate of a chord of 1,406,771 miles long, would be 359 miles long. This length would be a very snull fraction of the radius of the circle which I 2 1 1 6 New Theories in Astronomy. would be 685,400,000 miles long, but in a rotating sphere of the same dimension, we must acknowledge that the centri- fugal force at the middle of the arc would be greater how- ever small the difference than at its ends, and would sooner come to balance the force of gravitation ; therefore we must admit that the process of separation would begin there by abandoning a thin layer of matter, convex on the outer side and in a measure concave on the inner side, for the reason just given, much the same as a layer that could be pealed off from the equator of an orange the poles and equator of an orange are easily distinguished. As the velocity of rotation increased another layer would be abandoned following the first, so far curved on both sides, i.e. convex and concave, and the same process would continue on and on, according as the centrifugal force continued to balance that of gravitation, till the whole of the matter for all the attendants of the sun was abandoned ; so that in the process itself no such division of rings as we have been following could have taken place, but one continuous sheet, as it were, would be formed from first to last. Whether the thickness of the ring for Jupiter's system, or any other system or planet, was limited to the length of the chord we have been dealing with, or came to be many times greater or even less, makes no difference on our explana- tion. After being abandoned in a sheet, as we have shown it would be, the centrifugal force they had acquired would, for a time at least, keep the particles of the sheet near the radial positions they then occupied, and their mutual attraction would go on diminishing its thickness, till finally the radial attractions among the particles divided the sheet into entirely separate rings after the manner of those of Saturn ; which would in due course break up and form themselves into the smaller nebulae from which the planets were supposed to have been made. M. Faye has made it a great point against the nebula hypothesis that when these rings broke up, the rotary motions *>f the planets resulting from them would be retrograde, because the outer parts of them would be travelling at a slower rate than the inner ones, and has taken the trouble to New Theories in Astronomy. 1 1 7 construct a diagram to show how this would be the case ; but he himself has told us, in " L'Origine du Monde," that Laplace had duly considered this point, and had shown how the friction of the particles of the flat rings among themselves would, through course of time, retard and accelerate each other, so that a ring would come to revolve as if it were one solid piece, and consequently that the outer edge of the ring would come to be travelling faster than the inner one, which according to his (M. Faye's) own showing would produce, on breaking up, a planet with direct motion of rotation. Lap- lace's words, as cited by him, are: " Le frottement mutuel des molecules de chaque anneau a du accelerer les unes et retarder les autres jusqu'a ce qu'elles aient acquis une meme mouvement angulaire. Ainsi les vitesses reelles des molecules eloignees du centre de 1'astre ont ete plus grandes. La cause suivante a du contribuer encore a cette difference de vitesse : les molecules les plus distantes du soleil et qui, par les effets du refroidissement et de la condensation, s ; en sont rappro- chees pour former la partie superieure de 1'anneau ont toujours decrit les aires proportionnelles aux temps, puisque la force centrale dont elles etaient animees a e"te constamment dirigee vers cet astre ; or cette Constance des airs exige un accroisse- ment de vitesse a mesure qu'elles s'en sont rapprochees. On voit que la meme cause a du diminuer la vitesse des molecules qui se sont elevees vers 1'anneau pour former sa partie in- ferieure." In his method of bringing all the molecules of matter in a ring, to revolve round the centre as if they formed one sole piece, Laplace does not appeal to any accommodating force among them except friction, while he might have called in that of the collisions of the molecules amongst themselves. It is not to be supposed that each molecule would remain fixed in the position it occupied when separated from the nebulae, and only went on rubbing against and creating friction with its neighbours, and only creeping closer to the centre or farther from it, as it was acted upon by the attraction of the other parts of the ring. The molecules would be rushing against each other in all directions, in spite of, although in the 1 1 8 New Theories in Astronomy. main obedient to, the law of attraction ; and we could con- ceive the possibility of molecules gradually working their way from the extreme outer edge to the extreme inner edge of a ring, or vice versd, which would be a much more effectual means of bringing about one period of revolution throughout the whole ring, than the simple force of rubbing against each other. When physicists get a gas shut up in a close vessel, they grant to its molecules the power of committing exactly the same kind of freaks ; and a planetary ring is, to all intents and purposes, a closed vessel to our molecules ; because they have been placed in it by the laws of attraction and centrifugal force, and there is no other force acting upon them sufficiently powerful to liberate them from it. Therefore there is no reason why a molecule in a ring should be always wedged up in one place, especially after we have shown that each mole- cule of matter, in any of the rings we have been dealing with, must have had a much greater free path to move about in, than a molecule of gas shut up in any of the vessels used by physicists. We have no reason to look upon the rings of Saturn otherwise than as in process of being converted into one or more satellites, most probably more than one ; because if the matter they are composed of has been separated from the planet in the form of a sheet, the same as we have seen must have been the case with the matter separated from the original nebula for the planets, the sheet has been already divided into at least three distinct parts, and surely that cannot have been done without some object. If these rings have been left, as has been said, in order to show us how the solar system has been formed, that does not authorise us to con- clude that they will always remain in the form they have. There is no reason why the lesson should not be carried out to the very end, through the breaking up of the rings, forma- tion of spherical nebiculye, and finally satellites. It would be rash to assert that the matter of which any one of them is composed be it atoms, molecules, meteorites, or brick bats cannot, through friction and collisions of its particles among themselves, come to revolve around Saturn as if it were one New Theories in Astronomy. 1 1 9 solid piece. But should anyone do so, and adopt M. Faye's condemnation of Laplace's mode of forming rings, he must confess that when Saturn's rings are converted into satellites, their rotations must be retrograde ; and it might be, for him, an interesting inquiry to find out whether the rotations of the existing satellites are direct or retrograde. Astromoners have learnt the lesson as far as it has gone, have noted and registered the state of affairs as it is at present, and their successors will no doubt do the same as changes succeed each other. The day may be inconceivably remote, but it will inevitably come for the rings to be changed into satellites, unless they are disposed of in some other way. It has been said that were the rings to break up, in consequence of their being in a state of unstable equilibrium, they would fall back upon the planet, but that would depend on circumstances. If the motion of their revolution were stopped altogether, they would certainly fall back upon the planet ; but if it were not stopped then each molecule would retain its centrifugal force, and would revolve around the primary on its own account, just as, according to very general opinion, it does at present. \V e do not see why, or for what purpose, these rings could have been separated from Saturn merely to fall back upon him again. It would be rather a strange way of giving a lesson if it were stopped, by a cataclysm of some kind, just when the most interesting part of it was in a fair way of being exhibited. Such a proceeding would assuredly not suit the ideas of those who believe that the solar system has been self-formed by a simple process of evolution. During the whole process of separation of rings from the original nebula, the nebulous matter would be abandoned in what we may call the form of thin hoop-shaped rings, so that the equatorial region of the nebula would be flat as we have shown at p. 1 1 5 and when the nebula came to be so much reduced that it could abandon no more matter through centri- fugal force, its form would be, in some measure, like that of a rotating cylinder terminating at each end in a cap in the form of a segment of a sphere. When explaining the formation of planetary rings, we have seen that in the Jovian nebula the i 20 New Theories in Astronomy. length of the flat part would have come very soon to be nearly 1,500,000 miles, and that it would increase rapidly. But, remembering that the flattening of the equatorial part must have begun on the original nebula, we see that the flat part must have increased vastly in length before it reached Jupiter, and that by the time the residuary, or solar, nebula was reached which we made to be only a little over 63,000,000 miles in diameter the cylindrical part of it would bear no small proportion to that diameter. Taking this form of the nebula into consideration, and also the fact that the separation of matter from it by centrifugal force could not always be absolutely equal all around it, the swaying in its rotary motion produced by the all but inevitable inequality of mass, at the two ends of the cylindrical part, and at the sides of the segmental caps, may have been the cause of the differences in the inclinations of the orbits of the planets to the ecliptic ; and especially of why the difference came to be so much greater in the case of Mercury than in any of the others. In connection with this very reasonable conclusion as to the form of the nebula almost from the beginning, we may add that, when it ceased to throw off rings, it would be very much in the same condition as Saturn is at the present day. Therefore we may conclude with very great safety, that the present form of Saturn is that of a cylinder with segments of spheres forming the ends ; and in this manner can account for his square-shouldered appearance, which has puzzled more than one astronomer. The idea has been very general that in condensing and contracting, the nebula would gradually come to assume the form of a lens of a very pronounced character, from the circumference of which the rings would be abandoned one after the other ; but when thoroughly looked into, it is difficult to see how this could be the case. In a sphere of cosmic matter contracting equally all round towards the centre through the force of attraction, it is more natural to suppose that the separation of matter from its equator through centrifugal force, would have a tendency to diminish the equatorial more rapidly than the polar diameter, as we have been trying to New Theories in Astronomy. 1 2 1 show above, more especially as the attraction of the matter in the rings as they were abandoned one after the other would, in a constantly increasing degree, assist the centrifugal force in facilitating the separation by drawing the matter outwards. Matter falling in from the polar regions would afterwards require to have its motion turned off at right angles before it could be sent off by centrifugal force to the equator, an operation which would be more easily effected in the equa- torial regions, where the gravitating motion had only to be retarded ; and as very unequal amounts of density could not be created in the interior parts of such a sphere by gravita- tion, so as to cause pressure outwards, it is difficult to show how the polar diameter could be more rapidly reduced than the equatorial diameter, which was being continually shorn of its length. It may be said that all that we have been writing in the last few pages is absurd, because we have been pro- ceeding on the supposition that the condensation of the nebula was effected at or near its surface. Laplace procured this condition by piling up imponderable heat in his nebula, but he might have got it otherwise. Given a nebula such as the one we are dealing with of 6,600,000,000 miles in diameter, where would condensation be most active ? Most undoubtedly where there was the greatest mass of matter. Compare, then, the mass of i,oco,ooo miles in diameter at the surface with the mass of the same diameter at the centre, and we cannot hesitate for a moment in concluding that the most active condensation would not be very far from the surface. Not only so, but the same would continue to be the case, at least until the last ring was abandoned. Thus by working upon what may have appeared to be an absurd foundation, i.e. con- densation at the surface due to the intense heat of the nebula, we have been able to acquire more correct ideas than we had before, of how the solar system was elaborated. But we shall have much more to say on the same subject hereafter. There has been a great outcry raised about the rotation of the planets Neptune and Uranus being retrograde, as is correctly concluded to be the case from the revolution of their satellites being retrograde, but we do not see that there has been any 122 New Theories in Astronomy. good reason for it. Laplace, no doubt, concluded, wrongly, that the motions of all the bodies of the solar system as known to him were direct, and therefore used that conclusion in showing that there were 4000 milliards against I in favour of his hypothesis being right ; but at the same time it cannot be concluded that he thought that it would be destroyed by the motion of rotation of one or even several of the forty-three bodies turning out to be retrograde ; because, when discussing the hypothesis of Buffon, he states, most distinctly, that it is not necessary that the rotation of a planet should be in the same sense as that of its revolution, and that the earth might revolve from east to west, and at the same time the absolute movement of each of its molecules might be directed from west to east. His words as cited by M. Faye in " L'Origine du Monde," at page 158, are: "A la verite, le mouvement absolu des molecules d'une planete doit etre alors dirige dans le sens du mouvement de son centre de gravite, mais il ne s'ensuit point que le mouvement de rotation de la planete soit dirige dans le meme sens ; ainsi la Terre pouvait tourner d'orient en Occident, et cependant le mouvement absolu de chacune de ses molecules serait dirige d'occident en orient, ce qui doit s'appliquer au mouvement de revolution des satel- lites, dont la direction, dans I'hypothese dont il s'agit, n'est pas necessairement la meme que cellc de la projection des planetes." He seems to say, " This would suit Buffon's hy- pothesis, but I do not require it for mine." Even were this not so, it would not be very difficult to account for the retro- grade rotation of these two planets, but we are not yet pre- pared to show, in a convincing manner, how these motions were produced. We have to show first how the nebula itself was brought to the dimensions at which we took it up, and there is a great deal to be done before we can show that. Should our belief in being able to explain how the retro- grade rotations of Uranus and Neptune were brought about turn out to be unacceptable, we would not condemn the nebular hypothesis, because, as M. Faye himself says, if we add the asteroids to Laplace's 43 we should have somewhere about 500 bodies, all with direct motion, agreeing with the New r Pheories in Astronomy. 123 hypothesis, against 4 that do not, that is about 125 to I instead of 43 to I, which was all Laplace could claim. More- over, we have not been able to see that M. Faye's objections to it are well founded, rather the contrary ; nor can we agree with him when he says that when one point in a hypothesis is found to be erroneous it ought to be abandoned altogether, and something better sought for. Is his something any better? All acquired knowledge has been built up from ideas collected from all sides, and from errors reformed. What would a grammarian say were we to return to him his grammar as useless, because we had found one exception to one of his rules against 125 cases in which we had found it to be right ? Perhaps it would put him in mind of the name of a tree. And grammar is not the only case in which we say that the exception confirms the rule. In taking the nebula to pieces, we have taken no notice of the satellites of Mars, not only because they are so small that they would have had no sensible effect on our calculations, but because we cannot conceive that they could have been abandoned by the planet, when in a nebulous state, in the same manner as the planetary rings are supposed to have been by the parent nebula ; and we might simply refer to the dimensions, especially the thinness, we have found for the ring out of which Mercury was formed, for proof of our assertion ; but for more satisfactory corroboration, we will go a little deeper into the affair. Let us take the diameters of Mars and of the orbits of his satellites, as they are stated in text-books of astronomy; that is 2957, 11,640 and 29,200 miles re- spectively, and suppose the diameters of what in the method we have applied to the planets we would call the Deimos and Phobos nebulae to have been 40,000 and 20,420 miles also, respectively ; then these two diameters would make the breadth of the ring for the formation of Deimos to have been 9790 miles. With these data, if we go through a series of calculations with respect to this outer satellite, in all respects similar to those we have made for each of the rings of the planets, we shall find that the ring for Deimos would have been only 5 64 inches thick, without taking into account its 124 New Theories in Astronomy. condensation during the process of separation. This, of course, points out at once the impossibility of any such operation going on in Nature. We can imagine the possibility of a ring of even millions of miles broad, and of very great tenuity, holding together provided it be hundreds of thousands of miles thick, but to think of one 10,000 miles broad and less than 6 inches thick holding together is another affair altogether. With respect to Phobos, it is only necessary to say that he revolves round Mars in considerably less than one-third of the time that he ought to, and is therefore not a legitimate pro- duction of the nebular hypothesis any more than Deimos can be. Here, then, we have come upon two bodies, one of which has not been formed in the way, and the other has not the proper motion, prescribed in the hypothesis ; but we do not think ourselves justified in declaring it to be worthy of con- demnation on that account, seeing that we have found no other difficulty in working out the solar system from it. Moreover, it is not impossible, nor do we think it at all improbable, that through the course of time astronomers may discover that Phobos is a captured asteroid perhaps Deimos also gradually working its way into final annexation. And who can tell how many of these erratic bodies Jupiter and Mars may have captured already ? In the dark as it were, for they may have been too small to be noticed when they were being run in. Neither of these two worthies has ever been very much celebrated in song or history for respect for his neighbour's property. Jupiter is credited with sorting out the asteroids and arranging them in bands, and perhaps he has been human enough to exact a commission for his labour ; and it might be more in his line, and certainly much more easy for Mars, to take forcible possession of as many of them as came within his reach. New Theories in Astronomy. I 2 CHAPTER VII. PAGE 126 Analysis continued. No contingent of heat could be imparted to any planet by the parent nebula. 127 Only one degree of heat added to the nebula from the beginning till it had contracted to the density of ^th of an atmosphere. 127 Increase in temperature from o to possible average of 274 when condensed to 4,150,000 miles in diameter. 128 Time when the sun could begin to act as sustainer of life and light anywhere. Temperature of space. 129 The ether devised as carrier of light, heat, etc. etc. What effect it might have on the nebula. 130 First measure of its density, as far as we know. 133 The estimate too high. May be many times less. 134 Return to the solar nebula at 63,232,000 miles in diameter. 134 Plausible reason for the position of Neptune not conforming to Bode's Law. The ring being very wide had separated into two rings. 135 Bode's law reversed. Ideas suggested by it. 137 Rates of acceleration of revolution from one planet to another. 138 Little possibility of there being a planet in the' position assigned to Vulcan. 138 Densities of planets compared. Seem to point to differences in the mass of matter abandoned by the nebula at different periods. 139 Giving rise to the continuous sheet of matter separating into different masses. Probably the rings had to arrive at a certain stage of density before contracting circumferentially. 140 Possible average temperature of the sun at the present day. Central heat probably very much greater. 140 Churning of matter going on in the interior of the sun, caused by unequal rotation between the equator and the poles. COMING back to the period when we reduced the residuary nebula to the density of our atmosphere with temperature of o, or freezing water, we can with confidence afHrm that none of the rings abandoned by it for the formation of planets, could have carried with them any contingent of heat to help them in their formation any beyond the temperature of space for even if they did it would very soon be reduced to that. Each one of them in condensing, breaking up, rejoining 126 New J^heories in Astronomy. the broken fragments, converting itself into a minor nebula, and finally constituting itself as a planet, must have accumu- lated in the process its own heat requisite to convert it into a molten liquid globe a stage of existence through which they are all, that is, the major planets, acknowledged to have passed, or have to pass. During that process its primitive annular form, and the multitude of fragments into which each one of them broke up, would present sufficient radiating surface, not only to dispose of all the heat it could have brought with it from the nebula, but a considerable part of the little it could create for itself while contracting and condensing. We may even go farther and assert that no one of them would have any necessity for being supplied with extraneous heat until it had, in a great measure, exhausted the stock it had produced for itself, or so far as to cool down from the molten liquid to the solid state, and to the stage when vegetable and animal life could exist upon its surface. We have no reason for supposing that an enormous supply of extraneous heat was crammed into each nebula, merely to be radiated into space before condensation could take place, and thus retard the execution of the work in hand. If there are astronomers or physicists who believe that the sun could not acquire by gravitation, all the heat he must have expended during geo- logical time, they must look for it in some other source than that of useless and impossible cramming. Hitherto we have said nothing of heat being radiated into space by the nebula during our operations, because there could be almost absolutely none to radiate from it at o of temperature. No doubt there is a large range between this and the absolute zero of temperature which is 274 ; but we have seen, at page 99, that when the nebula was condensed from 403,000,000 to 274 times less dense than air, only one degree was added to its temperature that is, it was raised from - 274 to - 273 and that these 273 of absolute tem- perature were added to it in its condensation from being only 274 times less dense than air to atmospheric pressure, when its temperature became o of the ordinary Centigrade scale. Therefore the only period when there could be any measur- New Theories in Astronomy. 127 able radiation of heat into space would be between the times when the diameter of the nebula was (see Table III.) between 58,000,000 miles and 9,000,000 miles. Even when the end of this period came, the temperature, after a contraction of 49,oco,ooo miles in diameter, would be only 1 raised to o i n other words 273 raised to o and that would not furnish much positive heat heat such as we are accustomed to deal with to be radiated into space, whose temperature is without doubt somewhat warmer, so to speak, than 273. And let us repeat, and fix it in our memory, that this 273 was equal to only 1 of positive heat. If we now suppose the nebula to be condensed to one-tenth of its volume, with consequent density of 10 atmospheres, and corresponding diameter of about 4,150,000 miles, its tempera- ture would be 2740 of the ordinary Centigrade scale according to our mode of calculating hitherto provided no heat had been radiated from it into space in the meantime. Of course this could not be the case, but we have no means of calculating what the amount of radiation would be, and it will not make much difference on our operations to take no notice of it. However, it is here necessary to take into consideration that 2740 would be the average temperature of the nebula ; consequently, if condensation was most active where the greatest mass was, which certainly could not be at the centre or even near it, there also heat would be produced most rapidly, from whence it would spread towards the centre and surface. From the centre it would have no outlet, and would accumulate there as condensation advanced ; whereas from the surface it would be radiated into space, and would tend to decrease in amount, so that we may conclude that the surface must have been considerably colder than the centre. If to this we add the fact that, in order to get to the surface, heat would have to be conducted, or conveyed by currents ; over from one to two millions of miles, it becomes all the more certain that the central heat would be very much greater than that of the surface. How much less it would be at the surface we cannot pretend to calculate, but we may suppose it to have been from one-fifth to one-third of the average, or rather,. 128 New Theories in Astronomy. somewhere between 370 and 1000, which we have taken, at page 1 10, to be the temperatures of red-heat and white-heat. And thus we come to find that the nebula, which was supposed to be endowed with excessive heat when it extended far beyond the orbit of Neptune, could not have radiated either heat or light into space to much purpose, until it had been condensed into not much more than 4,000,000 miles in dia- meter. This then we must acknowledge to be the earliest period at which the sun began to act as the life sustainer of his system ; because, even were it to be found that there are other planets revolving within the orbit of Mercury, which we do not think very probable, we have seen that he could have no light or heat with sufficient vivifying power to radiate to . them, till his diameter was reduced to not far from what we have shown above. Even then the sun would most likely be very much less brilliant than he is now, but the light may have been sufficient to promote vegetation on Mars or the earth, if it was sufficiently cooled down from its molten state and not much heat would be required by him, as there would probably be a remnant of his own interior heat, still sensible at the surface, sufficient for vegetation at least. We have had occasion to refer several times to the temperature of space, and, though we cannot pretend to determine what it is, our operations enable us to show that it must be very much less than any estimate of it that has ever come under our notice. The nearest approach made to absolute zero by M. Olzewski, in his experiments on the liquefaction of gases, as reported in the " Scientific American " of June 2, 1 887, was - 225, or so-called 49 of absolute tempera- ture,* which would correspond to a density of O' 1788 of an atmosphere. This could not be the density of space, because it can be easily shown that our nebula, when at the same density, must have had a diameter of about 29,000,000 miles, and we must admit that were a globe of this diameter rotating in a medium of its own density, the friction between the two * From the same source, date June 6, 1896, we learn that the greatest cold probably ever reached was 243*5 or 31-5 of so-called absolute temperature, but that will have very little effect on our calculations, and so it is not worth while altering them all to suit. New Theories in Astronomy. 129 would have been so great as to put a stop to the rotation before very long. We may even say that distinct rotation could never have been imparted to it. Following the same reasoning, we must acknowledge that the density of space must be much lower than that of our original nebula, if that could be, and therefore we can assert with confidence that the temperature of space must be far below 225. Here our operations put us in mind that we have said nothing yet about the ether, or what effect it might have on our nebula and the bodies formed out of it. We have not done so for the simple reason that, with one exception, it has never been taken into account in any scientific work that has come into our hands, except so far as its being called upon to perform the offices of a dog that has been taught to carry and fetch, and we have not known how to deal with it. But as we have come along, we have seen that it must have had some- thing to do with the density, and consequent temperature, of all the bodies we have been dealing with, and that, if properly studied, it may enable us to account for some things that we have never seen, to our mind, properly explained. We know that it was devised, or conceived of somewhere between thousands of years ago and the birth of modern astronomy as a medium for carrying light, heat, and anything that was hard to move, through space, or to where it was wanted to be moved, by its vibrations or undulations, in the same way that sound is conveyed by wave motion, or vibration, through air, water, and a multitude of bodies ; and we understand that some time during that long period it began to be looked upon as a material substance. We are told that it is supposed to pervade all bodies of all classes, but we think this idea must be taken in a limited sense, because, whether it is combined with electricity, as some suppose, or is only a carrier of elec- tricity, a good conductor must have a larger supply of it than a bad one, and an absolute non-conductor, if there be such a substance, must contain none at all, always provided the ether is the conducting or carrying power. We are told also, that it is neither of the nature of a gas nor a liquid, but may be of the nature of a jelly, and of its nature we shall have more to K " OF THE '"^ NtvERSITY 130 New Theories in Astronomy. say hereafter. It was natural that it should be conceived to be a material substance, because if light and heat were to be carried from one place to another by wave motion, as sound is by water and air, then the medium for carrying it must be of the same nature as air and water or any other carrier of sound that is, it must be a material substance and, in conse- quence, possessed of some density or specific gravity. The only place where we have seen any density assigned to it has been, in a series of articles on the " Origin of Motion," pub- lished in ''Engineering" of 1876, where it is estimated to be __i___th* of the density of air. How this estimate was formed is explained in the number for December I, 1876, page 461, from which we make the following very long quota- tion, because we look upon it as of great importance. " Steel of the best quality in the form of fine wire has been known to bear a tensile strain represented by not less than 1 50 tons per square inch before breaking, and even this can- not be said to be the limit to the tensile strength of steel, since the tenacity increases as the diameter of the wire is reduced. Rejecting ' action at a distance/ therefore, these molecules of the wire must be controlled by some external agent, and therefore, the pressure of the external agent must at least equal the static value of the strain. The pressure of the ether therefore cannot be less than 150 tons per square inch. Now, since it is a known fact that the strain required to separate molecules in ' chemical union ' would be very much greater than in a mere case of ' cohesion/ it follows that the ether pressure must be greater than the above figure. If we suppose the strain required to separate the molecules of oxygen and hydrogen combined in the state of water (one of the most powerful cases of chemical union) to be only three times greater than in the case of the molecules of steel, then this would give 450 tons per square inch as the effective ether pressure. It may be taken as certain that the strain required * Years after this was written we have seen it stated that the density of the ether has been calculated from the energy with which light from the sun strikes the earth, and that to represent it there are twenty-seven cyphers after the decimal point before the figures begin. But as this gives something like one thousand quadrillionth part of the density of water, we refuse to accept or even think of it. New Theories in Astronomy. 131 would be greater than this, as it has not been found possible by any ordinary mechanical means to separate molecules in chemical union. However, as it is only our object to fix a limiting value for the ether pressure, or a value that is less than the actual fact, we will therefore take in round numbers 500 tons per square inch as the total ether pressure, having thus valid grounds for inferring that this estimate is within the facts as they actually exist. The existence of such a pressure as this might well be sufficient to strike one with astonishment and legitimately excite incredulity, if it were not kept in mind that this pressure is exercised against molecules of matter, a perfect equilibrium of pressure existing, so that it may be deduced with certainty beforehand, that, however great this pressure might be, it could not make itself apparent to the senses. The air exercises a pressure of some tons on the human body without such pressure being detected, how much more cause, therefore, is there for the perfect conceal- ment of the ether pressure, which is exercised against the molecules of matter themselves. This great pressure is the absolutely essential mechanical condition to enable the ether to control forcibly the molecules of matter in stable equi- librium, and to produce forcible molecular movements when the equilibrium of pressure is disturbed (as exemplified in the molecular movements of 'chemical action/ etc.). " It is generally admitted that the ether must have a very low density, one reason being the almost imperceptible resistance opposed by it to the passage of cosmical bodies (the planets, etc.) at high speed through its substance. The pressure of an aeriform body constituted according to the theory of Joule and Clausius, being less as its density is less, it will therefore be necessary to show that the ether can exert so great a pressure as the above, consistent with a very low density. From the known principles belonging to gases, the pressure exerted by an aeriform medium is as the square of the velocity of its component particles, .and as the density. We will, in the first place, consider what the density of the ether would be, if it only gave a pressure equal to that of the atmosphere (15 Ib. per square inch). From the above prin- K 2 132 New Theories in Astronomy. ciples, therefore, it follows that for the ether to give a pressure equal to that of the atmosphere, the ether density will require to be as much less than that of the atmosphere, as the square of the velocity of the other particles is greater than the square of the velocity of the air molecules. The velocity of the air mole- cules giving a measure of 15 Ib. per square inch is known to amount to 1600 feet per second. Taking, therefore, the square of the velocity of the ether particles infect per second, and the square of the velocity of the air molecules and dividing the one by the other, we have the number of times the ether density must be less than that of the atmosphere, in order for the ether to give a pressure of 1 5 Ib. per square inch, or we have 393'.i2Q,ooo,coo. This result shows therefore that the density of ether, if it only gave a pressure equal to that of the atmosphere, would be upwards of 390,000,000,000 times less than the density of th;e atmosphere. This result expresses such an infinitesimal amount of almost vanishing quantity, that the ether density might be well much greater than this. We will now, therefore, consider what the ether density would be to give a pressure of 500 tons per square inch. Pressure and density being proportional to each other, it follows that for the ether to give a pressure of 500 tons per square inch, the ether density would require to be as much greater than the above value, as 500 tons is greater than 15 Ib. Multiplying, therefore, the above value for the density by this ratio, we have I 500 x 2240 __ I x\ 393,120,000,000 15 5,264,800' or this shows that the density of the ether to give a pressure of 500 tons per square inch would be only __.JL_ th. of the density of the atmosphere. This value representing a density less than that of the best gaseous vacua is therefore quite consistent with the known fact of the extremely low density of the ether. It follows, therefore, as a mathematical certainty dependent on the recognised principles belonging .to gaseous New Theories in Astronomy. 133 bodies, that the ether could exert a pressure of not less than 500 tons per square inch consistent with such an extremely low density as to harmonize with observation." If the ether is possessed of a density equal to that shown above, then the density of our original nebula must have been greater than what we have shown it to be. The density we found for it was 4030 * O oo th that of air, or 0-000000002481 of an atmosphere, and 5 26 l, 8 Q tn is ec l ua l to 0*00000019 of an atmosphere ; if then we add these two together we get 0*0000001925 of an atmosphere as the density of our nebula. This comes to be very slightly greater than the density of the ether, and shows that the estimate in the foregoing quotation is too high ; unless it is asserted that the ether can exert no frictional action at all, which, we believe, no one has ever done ; while the absolute temperature of the nebula at the new density would be 0*000053, which would be a very small addition indeed to the 0*00000068, we found for it at first. On the other hand, when the nebula was reduced to 29,000,000 miles in diameter the density of the ether would have increased its density from 0-1788, which we showed it then to have, only to o* 17880019 of an atmo- sphere, which would make no appreciable difference on its temperature, and would be so immensely greater than the 0-00000019 of an atmosphere of the ether that it could hardly be supposed to have any effect in retarding the rotation of so much heavier a body. And should it be found that the density of the ether is \, -J, or less, or even a great deal more, than that shown in the above quotation, it would only have proportionately less effect on our nebula, in every sense, than what we have just shown. We may, therefore, conclude that the introduction of the element ether has not vitiated our operations in any way up till now, and we shall leave it until we have acquired more knowledge of its nature and effects. Although we have already condensed our nebula to some- where about 4,000,000 miles in diameter, where we have shown it might begin to radiate light radiation of heat may have begun when the diameter was ten times as great, or even before that we propose to return to the period when it had 134 New Theories in Astronomy. just abandoned the ring for the formation of Mercury and was 63,232,000 miles in diameter, and became what we have called the Solar nebula ; because there is a good deal to be learned from a careful study of our operations up to that period, and of what must have taken place during further condensation up till the final establishment of the sun such as it is at the present time. When the planet Neptune was discovered, Bode's Law fell into disrepute for a time, because the new planet was found to be much nearer to the sun than, according to it, it should have been. All the other planets occupied the places assigned to them within 5 per cent, of the exact appointed distance from the sun, but Neptune turned out to be 22^54 per cent, out of his exact place, and hence the discredit thrown upon the law. It was hard treatment for a servant that had helped so unmistakably as we know to have been the case to the discovery of the first four asteroids, which has afterwards been followed by the discovery of a whole host of them, and that had been pressed into the service for the discovery of the very planet which was the cause of its discredit but such is the world. However, first offences against the law are generally looked upon with merciful eyes, and the Series of Titius seems to have been so far received into favour again that, some astronomers are said to have been looking out for another planet farther off than Neptune, being convinced that there must be some reason why a law that has shown itself to be right in eight cases should be altogether wrong in the ninth. Here, we think that the most likely explanation that can be given is, that the ring out of which Neptune was formed divided itself, after breaking up, into two planets instead of one, and that this is the reason why, Bode's Law could not point out the true position of either of them. It is hard enough to believe that the ring out of which Uranus was made which we have seen may have been 954,000,000 miles broad, and over 3,400,000,000 miles in extreme diameter could have united its fragments, after breaking up, into one planet, and the difficulty of belief becomes greater the greater the diameter comes to be. We have, in our work, considered the breadth New Theories in Astronomy. 135 of Neptune's ring to have been 1,010,000,000 miles, but then we limited the diameter of the nebula to 6,600,000,000 miles we had to draw the line somewhere whereas it may have been a thousand million miles greater, which would very greatly increase the probability of two planets, perhaps even more, having been formed out of the ring. If it has been so, the law could not apply to the case. A new Act was required. Besides, it is not a law, never has been, but only a register of facts ; and we know that truths are often discovered from similar registers. It registers, and at the same time shows, that there is a nearly fixed inter-relation, even proportion, in the distances of the planets from the centre of the sun as far out as Uranus ; and were we to make a similar register, beginning at the (present) outside of the planetary system, and registering the number of revolutions, beginning with I for Neptune, rates of acceleration of revolution in number of days, and densities of the planets, we may draw from it some useful knowledge. But we shall first extend Bode's Law to embrace Neptune, and show the discrepancies between the actual positions of the planets and those pointed out by the law. Here we see that, with the exception of the first step from Neptune to Uranus which is only I "9577, we have an average gradation of acceleration of 2-5898 times, from one planet to another, from the outermost as far in as Mars ; and that had Neptune had the period of revolution sought for by Leverrier in his discovery of that planet, viz. 217-387 years, or 79>399'"O2 days, the average rate of acceleration would have been 2-5896 times, from planet to planet, as far in as Mars. This, we think, is pretty strong evidence that one law of acceleration was in force from the beginning of the separation of rings from the nebula up to the time when the ring for Mars was separated the departure from it in the case of Neptune, notwithstanding and goes far to prove that part of the nebular hypothesis which implies that each of the planets is now revolving round the sun in the orbit, and with the velocity, belonging to the centre of gyration of the ring out of which it was formed. From Mars to Venus the law the areolar law, of course had changed to a variable decreasing 136 New Theories in Astronomy. 8 D M f/^ ON rl- vo 10 10 i cT o * E ON 10 oo 3 *^ OO ^- O *-O MJ i^>. c< vO 5 OO 00 O O I ^ 00 4J CO to * " N t-N. IO fc o" o\ w 4 8 V? 2 ^ *^ c t^ VO 00 CD N sJ "^J. ^ ^J. K* N CD oo 3 C ; , i . ^ CD .^ as. ^ E *% o* "f vO ' O . O N 00 vo 53 cT co b ' 00 CO rt W IO H-( IO i i-T i-T ' j| f 8 o o | ON - ' 1 S vb N 'rf OO vO . vO vO O\ vo CJ OO .'i 00 vo 1-1 10 ON 00 ^ . fe 1 1 | 7 w 'a 3 oo ^ ^3. o * ^ t ? b CO CD Tf CD GO 00 CO 10 *~~> CD CD 4> IO Tj- CD 00 OO 1 N 'M 4 'I ^^ OO S J. 3 1! rj- 00 CD S3 Q/J 2^ N VO i rn C C ^ rv-? ^^ ^ | ^0 3 . g^ ' 53 ?D VO 1 vo O 10 10 HH VO VO * * ON ON ^ o i D. OO N < M p ' ON ON o ^ v O n rt >o . \o O * * s CD ^ R )5 ? i 13 C !> O W CD tc ri d< IO l~ VO vO *o 1^ . Crt 1 . J* i * C^l tr. r- 'J2 6 ^ oo oo" ^ rt ~ H- ON CD j r o 9 I^. IO g_) J> t/j CD *"D " *^n M *"* C ^^ s * ~ " ^ ^ > ^^^^ . 'S P- 1 *o ~ 0*73^^^ "S^O^CJc*- 1 ^ "^ fe g ^ c S ^ S ci ^ tt^ o "5 -2 u _rt C ^ - v ity of water. 393,724,522 491,596,266 i-oooo 2-2500 393,724,522 1,106,090,598 7900 7850 3-0000 3-0679 883,309,189 2-7500 2,429,097,520 . Volume to 9 I miles deep at ( density of water. 1,768,628,977 4,870,723,550 3-0339 3,928,912,640 14,777,288,178 7800 3*1359 4,809,069,650 3-IOI9 H,9I7,253,I47 7750 3-2038 4,747,808,450 3 -l6 9 8 15,049,403,225 7700 3-2717 4,686,939,950 3-2377 15,174,905,476 7650 3-3397 4,626,464,150 3'3057 15,293,702,541 7600 3-4076 4,566,381,050 3-3737 15,405,599,748 7550 3-4756 4,506,690,650 3 - 44i6 15,510,226,541 7500 3-5435 4,447,392,950 3-5095 15,608,125,558 7450 3-6114 4,388,487,950 3-5775 15,699,815,651 7400 3 -6794 4,329,975,650 3-6454 15,784,493,235 7350 3-7473 4,271,856,050 3-7I32 15,862,255,885 7300 3'8l52 4,214,129,150 3-78I2 15,934,465,142 7250 3-8832 4,^6,794,950 3-8492 16,000,335,122 7200 3-95" 4,099,853,450 3-9172 16,059,945,934 7I5 4-0191 4,043,304,650 3'985i 16,112,973,361 7100 4-0870 3,987,148,550 4-053I 16,160,311,788 7050 4' 1549 3,931,385,150 4-1210 16,201,238,203 7000 4-2229 3,876,014,450 80,329,049,377 4-1889 16,236,236,930 285,717,488,335 58 New Theories in Astronomy. TABLE IV. CALCULATIONS continued. Dia- meters in miles. Densities. Volumes Averages in Cubic Miles. ^^ Volumes at Density of Water in Cubic Miles. Observations. 7000 4-2229 80,329,049,377 4-1889 285,717,488,335 6950 4-2908 3,821,036,450 4-2568 16,265,387,960 6900 4*3587 3,766,451,150 4-3248 16,289,147,934 6850 4-4267 3,712,258,550 4-3927 16,306,838,133 6800 4-4946 3,658,458,650 4-4606 16,318,920,654 6750 4*5625 3,605,051,450 4-5285 16,325,475,491 6"JOO 4'6305 3,552,036,950 4-5965 16,326,937,841 6650 4-6984 3,499,415,150 4-6645 16,323,022,067 6600 4-7664 3,447,186,050 4-7324 16,313,463,263 6550 4*8343 3,395*349,650 4-8004 16,299,036,460 6500 4-9022 3,343.905,950 4-8682 16,278,802,946 6450 4-9702 3,292,854,950 4*9362 16,254,190,604 6400 5-038I 3,242,196,650 5-0042 16,224,600,476 6350 5-1060 3,191,931,050 5-0721 16,189,793,479 6300 5-1740 3, 142,058,150 5-1400 16,150,178,891 6284 Half vo the e 5-214 lume of \ arth J 962,684,511 5 2080 5,013,660,933 o' 352507 of the who e volume < of the earth at density of water. 129,961,924,688 518,596,945,467 6250 5-2420 2,129,893,439 5-2080 11,092,485,030 6200 5-3098 3,043,490,450 5-2759 16,057,151,265 6150 5-3778 2,994,795,650 5-3438 16,003,588,994 6lOO 5 '4457 2,946,493,550 5-4H8 15,954.833,794 6050 5*5137 2,898,584,150 5-4797 15,883,371,567 6000 5-5816 2,851,067,450 5-5477 15,816,866,892 146,826,249,377 609,405,243,009 New Theories in Astronomy. 159 TABLE I V. CALCULATIONS continued. Dia- meters in miles. Densities. Volumes in Cubic Miles. Averages of Densities. Volumes at Density of Water in Cubic Miles. Observations. 6OOO 5-58I6 146,826,249,377 5-5477 609,405,243,009 - 5950 5'6495 2,803,943,450 5-6156 15,745,824,838 5900 5'7I75 2,757,212,150 5-6835 15,670,605,255 5850 5-7850 2,710,873,550 5-7515 15,591,589,223 5800 5'8533 2,664,927,650 5-8194 15,508,275,967 5750 5'92I3 2,619,374,450 5-8873 15,421,043,199 5700 5-9892 2,574,213,950 5-9S53 15,330,206,336 5650 6'0572 2,529,446,150 6-0232 15,235,360,051 5600 6*1251 2,485,071,050 6'09I2 15,137,064,780 5591* 0^6478 whole v the 19 of the \ olume of > earth / 412,281,190 6T59I 2,539,281,080 [ Half mass of the J whole earth at (density of water. 168,383,592,967 735,584,493,738 555 6-1930 2,028,807,460 6*1591 12,495,628,024 5500 6*2610 2,397,498,950 6-2270 14,929,225,962 5450 6-3289 2,354,301,95 6*2950 14,820,330,775 5400 6-3968 2,311,497,650 6-3628 14,707.597,247 5350 6-4648 2,269,086,050 6*4308 14,592,038,570 5300 6-5327 2,227,067,150 6-4988 14,473,263,994 5250 6-6006 2,185,440,950 6-5667 14,351,135,086 5200 6-6686 2,144,207,450 6-6346 14,225,958,748 5150 5100 6-7365 i 2,103,366,650 6-8045 2,062,918,550 6*7026 14,098,025,308 6'7705 j 13,966,990,043 5050 6-8724 i 2,022,863,150 6-8385 ; 13,833,349,651 5000 6-9403 1,983,200,450 6-9064 13,696,775,588 I94,473849,377 905,774,812,734 i6o New Theories in Astromomy. TABLE IV. CALCULATIONS continued. Dia- meter in miles. Densities. Volumes in Cubic Miles. Averages of Densities. Volumes at Density of Water in Cubic Miles. Observations. 5OOO 6-9403 94,473,849,377 6 9064 905,774,812,734 4950 7-0083 1,943,930,450 6-9743 13,557,554,137 ' < . 4900 7-0762 1,905,053,150 7-0423 13,418,813,378 4850 7-I44I 1,866,568,550 7 i 102 13,271,675,704 4800 7-2I2I 1,828,476,650 7-1781 13,124,988,24! 475 7-2800 1,790,777,450 7-2461 12,976,152,480 4700 4650 4600 4550 7-3479 7-4I59 7-4838 7-55i8 1,753,470,950 1,716,557,150 1,680,036,050 1,643,907,650 7-3140 7-3819 7 '4499 7-5I78 12,824,887,528 12,671,453,226 12,516,100,569 12,358,568,931 About density of iron 4500 7-6197 1,608,171,950 7-5858 12,199,270,778 4450 7-6876 1,572,828,950 7-6537 12,037,960,935 ^ 4400 7-7556 1,537,878,650 7-7216 11,874,883,784 4350 7-8235 1,503,321,050 7-7896 11,710,269,651 f 4300 7-8914 1,469,156,150 7-8575 11,543,894,449 4250 7 '9594 1,435,383,950 7'9254 ",375,991,957 4200 8-0273 1,402,004,450 7*9934 11,206,782,371 4150 8-0953 i,3 6 9, OI 7,65o 8-0613 11,036,061,982 4100 8-1632 1,336,423,550 8-1295 10,864,454,250 4050 8-2311 1,304,222,150 8-1972 10,690,969,808 4000 8-2991 1,272,413,450 8-2651 10,516,624,406 226,413,449,377 1,147,552,171,299 New Theories in Astronomy. 161 TABLE IV. CALCULATIONS continued. Dia- meters in miles. Densities. Volumes in Cubic Miles. Averages of Densities. Volumes at Density of Water in Cubic Miles. Observations. 4OOO 8-2991 226,413,449,377 8-2651 1,147,552,171,299 3950 8-3670 1,240,997,450 8'333I 10,341,355,851 3900 3850 8'4349 8-5029 1,209,974,150 I,I79,343550 8 '4010 8-4689 10,164,992,834 9,987,742,590 1 * 3800 8-5708 1,149,105,650 8-5369 9,809,800,023 >, 1 3750 3700 8-6387 8-7067 1,119,260,450 1,089,807,950 8-6048 8-6727 9,631,012,320 9,451,577,408 3 O i i 3650 8-7746 1,060,748,150 8-7407 9,271,681,355 3600 8-8426 1,032,081,050 8-8086 9,091,189,137 i 3550 8*9105 1,003,806,650 8-8766 8,910,390,109 3500 8-9784 975,924,950 8-9445 8,729,160,715 3450 9-0464 948,435,950 9-0124 8,547,684,156 3400 9' "43 921,339,650 9-0804 8,366,132,559 3350 9-1822 894,636,050 9'I483 8,184,398,976 33 9-2502 868,325,150 9-2162 8,002,658,247 3250 9-3181 842,406,950 9 2842 7,821,074,605 3200 9 "3860 816,881,450 9-3522 7,639,638,697 3150 9'4540 791,748,650 9-4200 7,458,252,283 3100 9-5219 767,008,550 9-4880 7,277,377,122 3050 9-5899 742,661,150 9-5554 . 7,09.6,424,353 3000 9-6578 718,706,450 9-6239 6,916,759,004 245,786,649,377 1,320,251,473,643 M 162 New Theories in Astronomy. TABLE TV. CALCULATIONS continued. Dia- mete is in mi'es. Densities. Volumes in Cubic Miles. Averages of Densities. Volumes at Density of Water in Cubic Miles. Observations. 3OOO 9-6578 245,786,649,377 9-6239 1,320,251,473,643 2950 9*7257 695,144,450 9-6918 6,737,200,981 2900 9*7937 671,975,150 9'7597 6,558,275,371 2850 9-8616 649,198,550 9-8276 6,380,063,674 2800 9-9295 626,814,650 9-8956 6,202,697,051 2750 9*9975 604,823,450 9*9635 6,026,158,444 2700 10*0654 583,224,950 10-0315 5,850,621,086 2650 10-1334 562,019,150 10-0994 5,675,940,204 2600 10-2013 541,206,050 10-1674 5,502,658,393 2550 10*2692 520,785,650 10-2353 5,330,397,363 2500 10-3372 500,757,950 10-3032 5,059,409,310 2450 10-4051 481,122,950 10-3712 4,989,822,340 2400 10-4730 461,880,650 10-4391 4,821,618,293 f About density I of silver. 2350 10-5410 443,031,050 10-5070 4,654,927,242 2300 10-6089 424,574,150 10-5750 4,489,871,636 2250 10-6768 406,509,950 10-6429 4,326,444,747 2200 10-7448 388,838,450 10-7108 4,164,770,870 2150 10-8127 37I,559650 10-7798 4,005,338,715 2100 10-8807 354,673,550 10-8467 3,847,037,595 2050 10-9486 338,180,150 10-9147 3,691,134,883 2OOO 11-0165 322,079,450 10*9826 3,537,269,768 255,735,049,377 1,422,103,132,109 New Theories in Astronomy. TABLE IV. CALCULATIONS continued. Dia- meters in niile> Densities. Volumes in Cubic Miles. Averages Densities. Volumes at Density of Water in Cubic Miles. Observations. 2OOO 11-0165 255>735 49 377 10-9826 1,422,103,132,109 . !95 11-0845 306,371,450 II-0505 3,385,557,708 1900 11-1524 291,056,150 II'Il85 3,236,107,805 1850 11-2203 276,133,550 II-I864 3,088,940,344 I800 i i 2883 261,603,650 "'2543 2,944,165,858 1750 1700 11-3562 11-4242 247,466,450 2 33.72i,95o II*3223 II-3902 2,802,888,487 2,662,139,545 I About density | of lead. 1650 11-4921 220,370,150 11*4582 2,525,045,253 I6OO 11-5600 207,411,050 II-526I '2,390,640,503 1550 11-6280 194,844,650 11-5940 2,259,028,872 1500 11-6959 182,670,950 1 1 * 6620 2,130,308,620 M50 i i 7638 170,889,950 II-7299 2,004,522,025 1400 11-8318 159,501,650 II-7978 1,881,768,566 1350 11-8997 148,506,050 II-8658 1,762,143,088 1300 11*9676 137,903,150 "'9337 1,645,694,821 1250 12-0356 127,692,950 I2'00l6 1,532,519,609 1200 12-1035 117,875,450 12*0696 1,422,709,531 1150 12-1715 108,450,650 I2M375 i, 3*6, 3*9, 764 1 100 12-2394 99,418,550 12-2055 ',213,453,112 1050 12-3073 90,779,150 12-2734 1,114,168,820 1000 12-3753 82,532,450 12*3413 1,018,557,725 259,400,249,377 ,464,439,812,165 M 2 164 New Theories in Astronomy. TABLE IV. CALCULATIONS continued. Dia- meters in miles. Densities. Volumes in Cubic Miles. Averages of densities. Volumes at Density of Water in Cubic Miles. Observations. 1000 12-3753 59,400,249,377 12-3413 1,464,439,812,165 950 12-4432 74,678,450 I2-4093 927,507,290 900 I2'5III 67,217,150 12-4772 838,681,824 . 850 I2-579I 60,148,550 12- 545 1. 754,569,575 800 12*6470 53,472,650 12-6132 674,461,229 750 I2-7I49 47,189,450 12-6820 598,456,605 700 12-7829 41,298,950 12-7489 526,516,184 650 12-8508 35,801,150 12-8169 458,859,759 600 I2-9I88 30,696,050 12-8848 395,512,465 550 12-9867 25,983,650 12-9528 336,561,022 500 13-0546 21,663,950 13-0207 282,079,794 450 I3'I226 17, 736,95 13-0886 232,151,644 400 I3-I905 14,202,650 13-1566 186,858,585 350 13-2584 II,o6l,050 13-2245 146,276,856 3 00 13-3264 8,312,150 13-2924 110,488,423 250 13*3943 5,955,950 13-3604 79,573,874 2OO 13-4623 3,992,450 13*4283 53,6ll,8l6 150 I3-5202 2,421,650 i3*4963 32,683,315 100 I3-598I 1,243,550 13-5642 16,867,76! 50 I3-666I 458,150 13-6321 6,245,547 f About density ( of mercury. I3*7340 65,450 13-7001 896,672 259,923,849,377 1,471,098,672,405 True volume at density of water . 1,471,168,987,476 Deficiency 70,315,071 fAhrmt- * th I About 21i00( /n \ part. .,New Theories in Astronomy. 165 CHAPTER IX. PAGE 165 Inquiry into the Interior Construction of the Earth continued. 166 The earth gasiform at one period. Density including the moon may have been i th that of air. Must have been a hollow 10.000 body. Proofs given. 169 Division of the mass of the earth alone into two parts. 171 Division of the two masses at 817 miles from surface. 1 72 Reasons why the earth cannot be solid to the centre. 172 Gasiform matter condensing in a cone leaves apex empty. 1 73 Proportions of the matter in a cone. 174 Calculations of the densities of the outer half of the hollow shell of the earth. Remarks upon the condensation. 175 Calculations of inner half of the hollow shell. 177 Remarks upon position of inner surface of the shell. 179 Calculations of the same. THE INTERIOR OF THE EARTH AND ITS DENSITY continued. WHEN, according to the nebular hypothesis, the ring for the formation of the earth and moon had been thrown off by the nebula, and had broken up and formed itself into one isolated mass rotating or not on an axis, as the case may have been it must have been in a gasiform state. What was its density, more or less, may be so far deduced from Table III., where it will be seen that when it had condensed to about one- half of its volume, it must have had a density of only ^troo^ part of our atmosphere, and in which each grain of matter would have for its habitat 16 cubic feet of space, or a cube of 2-52 feet to the side. So that, with an average distance from its neighbours of 2^ feet, a grain of matter could not be looked upon as wedged-in in any way, and would be free to move anywhere. Now, supposing this earth-moon nebula to have been in the form of even an almost shapeless mass> and that .it was nearly homogeneous as it could hardly be otherwise after the tumbling about it had in condensing from a flat ring 1 66 New Theories in Astronomy. its molecules would attract each other in all directions, and as the mass without having arrived perhaps at the stage of having any well defined centre would have an exterior as well as an interior, the individual molecules at the exterior would draw those of the interior out towards them, just as much as those at the interior would attract those of the exterior in towards them ; but as the number of those at the exterior would owing to the much greater space there, being able to contain an immensely greater number be almost in- finitely greater than of those nearer to the central part, the latter would be more effectually attracted, or drawn, outwards than the former would be inwards, and there would be none left at the interior after condensation had fairly begun. The mass would speedily become a hollow body, the hollow part gradually increasing in diameter. But let us go deeper into the matter. Let us suppose that the whole mass had assumed nearly the form of a sphere. We have already shown that, although the general force of attraction would cause all the component particles of the sphere to mutually draw each other in towards the centre, yet the more powerful tendency of the particles at the exterior due to their greatly superior number would at first be to draw the particles near the centre outwards towards them, and that there would consequently be a void at the centre, for a time at least. Of course it is to be under- stood that each part of the exterior surface would draw out to it the particles on its own side of the centre, just in the same manner as the four masses we placed at the centre were shown to be drawn out by those at London, Calcutta, and their antipodes. Now we must try to find out what would be the ultimate result of this action ; whether it would be to form a sphere solid to the centre, or whether the void at first established there would be permanent. In order to show how the heat of the sun is maintained by the condensation and contraction of that luminary, Lord Kelvin in his lecture delivered at the Royal Institution, on Friday, January 21, 1887 described an ideal churn which he supposed to be placed in a pit excavated in the body of the New Theories in Astronomy. 167 sun, with the dimension of one metre square at the surface, and tapering inwards to nothing at the centre. In imitation of him, we shall suppose a similar pit of the same dimensions to be dug in the spherical mass, out of which we have sup- posed the earth to have been formed ; only we shall call it a pyramid instead of a pit. This we shall suppose to be filled with cosmic matter, and try to determine what form it would assume were it condensed into solid matter, in conformity with the law of attraction. The apex of our imaginary pyra- mid would, mathematically speaking, have no dimension at all, but we shall assume that it had space enough to contain one molecule of the cosmic matter of which the sphere was formed. This being so arranged, we have to imagine how many similar molecules would be contained in one layer at the base of the pyramid at the surface of the sphere, and we may be sure that when brought under the influence of attrac- tion, the great multitude of them would have far more power to draw away the solitary molecule from the apex, than the single one there would have to draw the whole of those in the layer at the base in to the centre of the sphere. A mole- cule of the size of a cubic millimetre would be an enormously large one, nevertheless one of that size placed at the apex of the pyramid would give us one million for the first layer at the base, and shows us what chance there would b"e of the solitary one maintaining its place at the apex. At the dis- tance of one-twentieth of the radius of the sphere from the centre, the dimension of the base of the pyramid would be one-twentieth of a square metre, and the proportion of pre- ponderance of a layer of molecules there would be as 25 to I, so that the molecule at the centre would be drawn out almost to touch those of that layer ; at one-tenth of the radius from the centre, the preponderance of a layer over the solitary central molecule would be as 10,000 to I ; and so on pro- gressively to 1,000,000 to i, as we have already said. Following up this fact, if we divide the pyramid into any number of frusta, the action of attraction will be the same in each of them ; the molecules in the larger end of each will have more power to draw outwards those of the small end, 168 New Theories in Astronomy. than they will have to draw inwards those of the larger end ; and then the condensed frusta will act upon each other in the same manner as the molecules did, the greater mass of those at the larger end, or base, drawing down, or out whichever way it may seem best to express it a greater number of the frusta at the smaller end of the pyramid, until, in the whole of it, a point would be reached where the number of molecules in the various frusta drawn down from the apex would be equal to those drawn up from the base, leaving a part of the pyramid void at each end, because we are dealing with attrac^ tion, not gravitation, and there would be no falling to the base or apex, but concurrence to the point, just hinted at, where the outwards and inwards attractions of the masses would balance each other. This point of meeting of the two equal portions of cosmic matter may be called the plane of attrac- tion in the pyramid. The whole pyramid would thus be reduced to the frustum of a pyramid, whose height would be as much more than double the distance from the plane of attraction to its base, as would be required to make the upper part above the plane of attraction equal in volume, or rather in number of molecules, to the lower part It would be im- possible for us to explain how, in a pyramid such as the one we have before us, the action of attraction could condense, and at the same time cram, the whole of the molecules con- tained in it into the apex end. We must not, however, forget that there are two sides to a sphere, as well as to a question, and that we must place on the opposite side to the one we are dealing with, another equal pyramid with apex at the centre and base at the surface, at a place diametrically opposite to the first one, and that the tendency of the whole of this new pyramid would be to draw the whole of the first one in towards the centre of the sphere. But in the second, the law of attraction would have the same action as in the first ; the molecules of the matter contained in it near the base would far exceed, in attractive force, those near the apex, and would draw them outwards till the whole were concentrated in a frustum of a pyramid, exactly the same as the one in the first pyramid. And while the whole New Theories in Astronomy. 169 masses of matter in the two pyramids were attracting each other at an average distance, say, for simplicity's sake, of one- half the diameter of the sphere, the molecules in each of them would be attracting each other from an average distance of one-quarter the diameter of the sphere ; their action would consequently be four times more active, and they would con- centrate into the frusta as we have shown, before the two pyramids had time to draw each other in to the centre. There would be then two frusta of pyramids attracting each other towards the centre with an empty space between them. Here then we have two elements of a hollow sphere, one on each side of the centre, and if we suppose the whole sphere to have been composed of the requisite number of similar pyra- mids, set in pairs diametrically opposite to each other, we see that the whole mass of the matter out of which the earth was formed must have by the mutual attractions of its molecules formed itself into a hollow sphere. All that has been said must apply equally well whether we consider the earth to have been in a gasiform state/or when by condensation and consequent increase of temperature it had been brought into a molten liquid condition. For up to that time it must have been a hollow sphere, and we must either consider it to be so still, or conceive that the opposite sides have continued to draw each other inwards till the hollow was closed up ; in which case, the greatest density would not be at the centre, but at a distance therefrom corresponding to what has been called the plane of attraction of the pyramid. That the opposite sides have not yet met will be abundantly demonstrated by facts that will meet us, if we try to find out what is the greatest density of the earth at the region of greatest mass or attraction, wherever that may be. Seeing that the foregoing reasoning forces us to look upon the earth as a hollow sphere, or shell, in which the whole of the matter composing it is divided into two equal parts, attracted outwards and inwards by each other to a common plane, or region of meeting, we shall divide its whole volume into two equal parts radially, that is, one comprising a half from the surface inwards, and the other a half from the centre i/o New Theories in Astronomy. outwards that is to say, each one containing one-half of the whole volume of the earth. Referring now to our calculations, Table IV., we find that the actual half volume of the earth is comprised in very nearly 817 miles from the surface, where the diameter is 6284 miles, because the total volume at 7918 miles in diameter is 259,923,849,377 cubic miles. This being the case, we cannot avoid coming to the conclusion, after what has just been demonstrated by the pyramids that if one- half of the whole volume is comprehended in that distance from the surface, so also must be one-half of the mass. But for further substantiation of this conclusion let us return to the table of calculations. There we find that from the surface to the depth of 817 miles where the diameter would be 6284 miles which comprehends one-half of the volume the mass at the density of water is shown to be only 518,596,945,467 miles instead of 735,584,493,738 cubic miles, which is the half of the whole mass of the earth reduced to the density of water. That is, the outer half of the volume gives only 70* 5 per cent, of half the mass, while the inner half of the volume gives not only one-half of the mass but 29*5 per cent, more ; or, to put it more clearly, the mass of the inner half- volume is I '84 times, nearly twice as great, as the mass of the outer half-volume. On the other hand, we have to notice that the line of division of the mass into two halves falls at 1163*25 miles from the surface, where the diameter is 5591*5 miles ; so that on the outer half of the earth, measured by mass, 64*74 per cent, of the whole volume of the earth con- tains only one-half of the mass, whereas on the inner portion, measured in the same way, 35*26 per cent, of the same whole contains the other half. All these results must be looked upon as unsatisfactory, or we must believe that two volumes of cosmic matter which at one time were not far from equal, had been so acted upon by their mutual attractions that the one has come to be not far from double the mass of the other ; that the vastly greater amount of cosmic matter at the outer part of a nebula has only one-half of the attractive force of the vastly inferior quantity at the centre. This we cannot believe if the original cosmic, or nebulous, matter was homogeneous ; New Theories in Astronomy. 171 and if it was not homogeneous we have, in order to bring about such result, to conceive that the earth was built up, like any other mound of matter, under the direction of some superintendent who pointed out where the heavier and where the lighter matter was to be placed. We shall now proceed to find out what would be the internal form, and greatest density of the earth, under the supposition that it is a hollow sphere divided into two equal volumes and masses exterior and interior meeting at 817 miles from the surface ; but before entering upon this subject we have something to say about the notion of the earth being solid to the centre. We are forced to believe that, according to the theory of a nucleus being formed at the centre as the first act, the matter collected there must have remained stationary ever since, because we cannot see what force there would be to uniform the nucleus just formed ; gravitation, weight falling to a centre, would only tend to increase, condense, and wedge in the nucleus more thoroughly. Attraction, as we have shown, would not allow the matter to get to the centre at all. Convection currents, or currents of any kind, could not be established in matter that was being wedged in constantly. Moreover, when in a gasiform state, it would be colder than when condensed by gravitation to, or nearly to, a liquid or solid state, and heat would be produced in it in proportion to its condensation, that is, gradually increasing from the surface to the centre in the same manner as density, which, when the cooling stage came, would be conducted back to the surface to be radiated into space, but could not be carried by con- vection currents because the matter being heavier there than any placed above it, and being acted upon by gravitation all the time, would have no force tending to move it upwards ; and above all, when solidification began at the surface, it is absurd to suppose that the first formed pieces of crust could sink down to the centre through matter more dense than themselves ; unless it was that by solidification they were at once converted into matter of the specific gravity of 13 "734. Even so the solid matter would not be very long in being 172 New Theories in Astronomy. made liquid again by meeting with matter not only hotter than itself, but constantly increasing in heat through continual condensation, which would act very effectively in preventing any convection current being formed to any appreciable depth, certainly never to any depth nearly approaching to the centre. If solidification began first at the centre as some parties have thought might be the case owing to the enormous pressure it would be subjected to there, before it began at the surface, then, without doubt, the central matter must have remained where it was placed at first, up to the present day. This would suit the sorting-out theory very well, as all the metals would find their way to the centre and there remain ; but judged under a human point of view, it would be considered very bad engineering on the part of the Supreme Architect to bury all the most valuable part of His structure where they could never be availed of ; or that He was not sufficiently fertile in resources to be able to construct His edifice in a way that did not involve the sacrifice of all the most precious materials in it. Man uses granite for foundations follow- ing the good example He has actually given we believe, and are trying to show and employs the metals in super- structures ; but some people may also think that it was better to keep the root of all evil as far out of man's reach as possible. What a grand prospectus for a Joint Stock Company might be drawn up, on the basis of a sphere of a couple of thousand miles in diameter of the most precious metals, could only some inventive genius discover a way to get at them ! Returning to our pyramids. We know that the centre of gravity of a pyramid is at one-fourth of its height, or distance from the base, and if we lay one of 3959 miles long (the radius of the earth) over a fulcrum, so that 989! miles of its length be on one side of it and 2969 J miles on the other, it will be in a state of equilibrium. This does not mean, however, that .there are equal masses of matter on each side of the fulcrum, for we know that the mass of the base part must be con- siderably greater than that of the apex part, and that it must be counterbalanced by the greater leverage of the apex part, due to its greater distance from the point of support. This being so, in the case of a pyramid consisting of gasiform, New Theories in Astronomy. \ 73 liquid, or solid matter, the attractive power of the 989! miles of the base part would be greater than that of the 2969! miles of the apex part, and the plane of equal attraction of the two parts would be less than 990 miles from the base of the pyramid. This is virtually the same argument we have used before repeated, but it is placed in a simpler and more practical light, and shows that the plane of attraction in a pyramid will not be at its centre of gravity but nearer to its base, and that it must be at or near its centre of volume. Thus the plane of attraction in one of the pyramids we have been considering of 3959 miles in length, and consequently the radial distance of the region of maximum attraction of the earth, would not be at 990 miles from the base or surface, but at some lesser distance. Now, if we take a pyramid, such as those we have been dealing with, whose base is I square and height 3959, its volume would be the square of the base multiplied by one- third of the height, that is I 2 X = 1319-66, the half of which- is 659*83. Again, if we take the plane of division of the volume of the pyramid into two equal parts to be o* 7937 in length on each side, and consequently (from equal triangles) the distance from the plane to the apex to be 0-7937 f the total height of 3959, which is 3142-258; then, as we have divided it into a frustum and a now smaller pyramid, if we multiply the square of the base of this new pyramid by one-third of the height we have 0-793 7 2 X , or 0*62996 x IO47'4I9 = 659-83, which is equal to the half-volume of the whole pyramid as shown above. Thus we get 3959 less 3142*258 = 816*74 miles as the distance from the base of the plane of division of the pyramid into two equal parts, which naturally agrees with the division of the earth into the two equal volumes that we have extracted from the table of calculations, where we have supposed the earth to be made up of the re- quisite number of such pyramids. So that it would seem that we are justified in considering that the greatest density of the earth must be at the meeting of the two half-volumes, outer and inner, into which we have divided it. 174 New Theories in Astronomy. Considering, then, that one-half of the volume and mass of the earth is contained within 817 miles in depth from the surface, this half must have an average density of 5 '66 times that of water, the same as the whole is estimated to have. Also, as we have seen already, that, taking its mean diameter at 7918 miles, its mass will be equivalent to 1,471,168,987,476 cubic miles, one-half of this quantity, or 735,584,493,738 cubic miles will represent the half-volume of the earth reduced to the density of water. With these data let us find out what must be the greatest density where the two half-volumes meet, supposing the densities at the surface and for 9 miles down to remain the same as in the calculations we have already made, ending with specific gravity of 3 at 7900 miles in dia- meter. Following the same system as before when treating of the earth as solid to the centre, and using the same table of calcu- tions for the volumes of the layers : If we adopt a direct pro- portional increase between densities 3 at 7900 miles and 8 8 at 6284-5 miles in diameter, multiply the volumes by their respective densities, and add about 31 per cent, of the follow- ing layer, taken at the same density as the previous or last one of the number, we shall find a mass (see Table V.) of 735,483,165,215 cubic miles at the density of water, which is as near the half mass 735,584,493,738 cubic miles as is neces- sary for our purpose. It would thus appear that if the earth is a hollow sphere, its greatest density in any part need not be more than 8*8 times that of water, instead of 13 "734 times, if we consider it to be solid to the centre. Let us now try to find out something about the inner half- mass of the earth, and the first thing we have got to bear in mind is, that where it comes in contact with it, its density must be the same as that of the outer half-mass at the same place, and continue to be so for a considerable distance, vary- ing much the same as the other varies in receding from that place, and diminishing at the same rate as it diminishes. This being the case and we cannot see how it can be other- wise if we attempt to distribute the inner half-mass over the whole of the inner half-volume, and suppose that its density decreases from its contact with the outer half where it was New Theories in Astronomy. 175 found to be 8 8 times that of water to zero at the centre, in direct proportion to the distance ; then, it is clear that at half the distance between that place and the centre, the density must be just 4*4 times that of water. Now, if we divide the outer moiety of the inner half-mass of the earth that is, the distance between the diameters of 6284*5 miles and 3142*25 miles into layers of 25 miles thick each, take their volumes from Table IV., and multiply each of them by a corre- sponding density, decreasing from 8-8 to 4*4, we shall obtain a mass far in excess of the whole mass corresponding to the inner half of the earth. This shows that a region of no density would not be at the centre but would begin at a distance very considerably removed from it. It is another notice to us that the earth must be a hollow sphere. But why should there be a zero point or place of no density ? And what would a zero of no density be ? It would represent something less than the density of the nebulous matter out of which the earth was formed ; and all that we have contended for, as yet, is that there is a space at the centre where there is no greater density than that corresponding to the earth nebula ; but we must now go farther. If the earth is a hollow sphere, it must have an internal as well as an external surface. But how are we to find out what is the distance between these two surfaces ? Let us, to begin, take a look at the hollow part of the sphere. From the time of Arago it began to be supposed that there is a con- tinual deposit of cosmic matter upon the earth going on, and since then it has been proved that there is a constant and enormous shower of meteors and meteorites falling upon it. But although this is the case on the exterior surface, it may be safely asserted that on the interior surface, where the supply of cosmic matter must have been limited from the beginning, there can be no continual deposit of such matter going on now ; nor can there have been from, at least, the time when the earth changed from the form of vapour to a liquid state. We may, therefore, be sure that there is no undeposited cosmic matter of any kind in the hollow of the sphere, and that, as far as it is concerned, there is an absolute vacuum. 176 New Theories in Astronomy. TABLE V. CALCULATIONS OF THE VOLUMES AND DENSITIES OF THE OUTER % HALF OF THE EARTH TAKEN AS A HOLLOW SPHERE AT THE DIAMETERS SPECIFIED, AND REDUCED TO THE DENSITY OF WATER. With mean diameter of 7918 miles. Diameter of half-volume at 6284*5 miles, and density there of 8*8 times that of water. Dia- meters in miles. Densities. Volumes in Cubic Miles. Averages of Densities. Volumes at Density of Water in Cubic Miles. Observations. 79 l8 79H 7905 2'OOOO 2 -5000 129,961,924,377 I '0000 2*2500 735,584,493,738 , Half- volumes of J the earth actual 1 and at density of v water. 1 Density at 7914. I miles in diameter. \ The 2 miles above I being at density of I water. 393>724,522 491,596,266 393,724,522 1,106,090,598 7900 3-0000 883,309,189 2-7500 2,429,097,520 ( Volume to 9 miles \ deep at density of ( water. 1,768,628,977 3,928,912,640 7850 3-I823 4,870,723,550 3-0912 15,056,380,638 7800 3'3625 4,809,069,650 3-2724 I5,737,I995 2 3, 775 3'5437 4,747,808,450 3-453! 16,394,666,359 7700 3-7250 4,686,939,950 3-6343 17,023,745,860 7650 3-9062 4,626,464,150 3-8156 17,652,736,611 7600 4-0875 4,566,381,050 3-9969 18,251,368,419 7550 4-2688 4,506,690,650 4-1781 18,829,404,185 7500 4-4500 4,447,392,950 4-3594 19,387,964,826 : : 7450 4-6312 4,388,487,950 4-5486 19,926,368,386 7400 4-8125 4, 3 2 9>975, 650 4-7219 20,445,712,022 7350 4'9938 4,271,856,050 4-9031 20,945,337,398 7300 5-I750 4,214,129,150 5-0844 21,426,318,250 7250 5-3562 4,156,794,950 5-2656 21,888,019,489 72OO 5-5375 4,099,853,450 5-4469 22,331,491,757 7I5 5-7I87 4,043,304,650 5-6281 22,756,152,901 7100 5-900 3,987,148,550 5-8093 23,162,542,072 32,521,649,777 315,144,321,336 New Theories in Astronomy. 177 TABLE V '.continued. Dia- meters in miles. Densities. Volume in Cubic Miles. Averages of Densities. Volume at Density of Water in Cubic Miles. Observations. 7100 5- 9 000 72,521,649,777 5-8093 315,144,321,336 7050 6-0813 3>93I,385>I50 5-9907 23,551,749,018 7000 6*2625 3,876,014,450; 6*1719 23,922,373,584 6950 6-4438 3,821,036,450 6*3532 24,275,808,774 6900 6-6250 3,766,451,150 6-5344 24,611,498,395 6850 6-8062 3,712,258,550 6-7156 24,930,043,518 6800 6-9875 3,658,458,650 6-8968 25,231,657,617 6750 7-I688 3,605,051,450 7-0782 25,517,275,173 6700 7'3500 3,552,036,950 7'2594 25,785,657,035 6650 7-53I2 3,499,4I5I50 7-4406 26,037,748,365 6600 7-7I25 3,447,186,050 7-6218 26,273,762,636 6550 7-8938 3>395,349,650 7-8032 26,494,592,389 6500 8-0750 3,343,905,950 7-9844 26,699,082,667 ' . " 6450 8-2562 3,292,854,950 8-1656 26,888,136,380 6400 8-4375 3,242,196,650 8-3468 27,061,966,998 6350 8-6188 3,191,931,050 8-5282 27,221,426,381 ;. . , ' 6300 8-8000 3,142,058,150 8-7094 27,365,441,252 6284^ 8-8000 962,684,511 8-8000 8,471,623,697 129,961,924,688 735,484,165,215 True half-volume at density of water 735,584,493,738 Deficiency . , 100,328,522 As to how far the internal surface is from the centre, it may be possible to designate a position, or region, from which it cannot be very far distant, although we can never expect N 178 New Theories in Astronomy. to be able to point out exactly where it is. Going back to the time when the whole earth was in a molten liquid state, and just before the outer surface began to become solid, it is certain that the interior surface must have been in the same liquid condition, whatever may have been the condition of the mass of matter between the two surfaces, owing to the pressure of superincumbent matter ; nay, we may be sure that what- ever may be its state now, it continued liquid long after the other became solid, because it had no outlet by which to get rid of its melting heat by radiation, nor weight of superin- cumbent matter to consolidate it ; and it would always be much hotter than the outer surface. At that time we have every reason to believe that the outer surface was at least as dense as it is now, there being no water upon it to lower its average density, as is the case at the present day ; and we have equal reason to consider that the density at the inner surface, whether liquid or solid, is now at least equal to what the outer surface was then. Duly considering, therefore, the absence of water from the interior surface, we shall suppose that the first layer of 25 miles thick upon it will have an average density of 2^ times that of water, terminating at 3 times, which is the density we have taken for the outer surface at 9 miles deep. But there is another contingency, which it will be necessary to take into consideration before going any farther. It has been understood as it is certainly the truth in the calculations made with respect to the outer half of the mass of the earth, that the increase of density in descending was due to the pressure of the superincumbent matter, caused by the attraction for it of the inner half, as well as that of the whole of both the outer and inner halves on the other side of the hollow interior. In the case of the inner half we have now to consider that the attraction of the outer half alone would be the effective agent, and that the superincumbent pressure that is, of course, the pressure acting from the centre outwards would be interfered with, or perturbed, by the attraction of the mass on the other side of the hollow interior, so that it would not exert its full power in that New Theories in Astronomy. 1 79 direction. But that does not mean that the density would be in any way diminished. The attractions of the planets for each other perturb them in their revolutions around the sun, accelerating or retarding each other, but do not increase or diminish their density or mass ; only it will lead us to expect that the same depth of 817 miles will not produce the same amount of pressure outwards at the meeting of the two halves as it does inwards, and that to obtain an equal pressure a greater depth will be required. We believe that an expert mathematician, taking as bases two opposite pyramids in a sphere, similar to those we have used in a former part of our work, could point out, with very approximate accuracy, what ought to be the distance of the inner surface of the shell from the centre provided a maximum density were determined for the earth but that goes beyond our powers, and we shall limit ourselves to the use of our own implements ; which will cause us to depart from the statement we have made, that the density of the inner half must decrease from the place of meeting of the two halves, at the same rate as the outer half had increased. It must decrease much more rapidly than the other increased. All this premised, and having estab- lished a density of 3 for the interior surface, we may proceed to calculate where that surface ought to be, so as to give for the interior half of the earth a mass equal to 735,584,493,738 cubic miles of water. If we begin our operations with a density of 8*8 times that of water at the meeting of the two halves of the shell, and diminish it for any considerable distance at the same rate as it increased when we were finding the mass of the outer half, that is O'i8i2 for each layer, we soon find that before we could make up the whole mass of the inner half of the shell, the density would be decreased to at least that of water, which cannot be, as there can be no liquid or solid matter of any kind of so low density anywhere in the interior half of the shell. Furthermore, if we decrease it at the same rate as the volumes of the different layers of the earth de- crease as they approach the centre, it involves a mass of calculation that serves no useful purpose, as such calculations N 2 180 New Theories in Astronomy. bring no contingent of satisfaction with them ; because all the densities with which we are dealing have to be brought to a rational form before we can frame a proper approximate idea of what the interior construction of the earth is, as will be seen hereafter ; and because it takes no account of the perturbation above alluded to produced by the attraction of the matter on the opposite side of the hollow. But, in order to get such a result as we can with our limited powers, if we begin with a density of 8 '8 at the diameter of 6284*5 miles and fix the density of 3 which we have adopted above at the diameter of 3200 miles, we shall get a mass some- what less than one-half of the earth ; and with a density of 2*91 at 3150 miles diameter we get a mass of 735,713,884,116 cubic miles of water, which is rather greater than one-half of the mass required (see operations of Table V.). This density of 2*91 reduced to 2*5, as we mentioned, might be done when we were fixing the number 3, would make very little difference on the resulting mass, compared with what we have been in quest of. Here we may state that we found that, had the calcula- tions been made with documents of density proportioned to the decrease of the volumes of the layers of the earth as they approached the centre, the density would have been reduced to 2*25 at 3150 miles in diameter ; which tends to show that should that process be considered to be more accurate, it would not have made any great difference on the result. With all, we may consider that it has been demonstrated, that the greatest density of the earth is not necessarily greater at any part of its interior than 8 8 times that of water. New Theories in Astronomy. 181 TABLE VI. CALCULATIONS OF THE VOLUMES AND DENSITIES OF THE INNER HALF OF THE EARTH, ON THE SAME DATA AS THOSE FOR THE OUTER HALF. Diameters in Miles. Volumes in Cubic Miles. Densities. Volumes at Density of Water in Cubic Miles. Observations. 6284^ 129,961,924,688 735,584,493,737 ( Half-volumes of i the earth. 6250 2,129,893,439 8'800 18,743,062,263 6200 3,043,490,450 8-705 26,493>584367 6150 2,99*.795>650 8-610 25,785,090,546 6lOO 2,946,493,550 8-5I5 25,089,392,578 6050 2,898,584,150 8-420 24,406,078,543 6000 2,851,067,450 8-325 23,735,136,521 5950 2,803,943,450 8-230 23,076,454,654 5900 2,757,212,150 8-135 22,429,920,840 5850 2,710,873,550 8*040 21,795,423,342 5800 2,664,927,650 7-945 21,172,850,179 5750 2,619,374,450 7-850 20,562,089,432 5700 2,574,213,950 7'755 19,963,029,182 5650 2,529,446,150 7-660 19,375,557,509 5600 2,485,071,050 7-565 18,799,562,493 5550 2,441,088,650 7-470 18,234,932,216 5500 2,397,498,95 7-375 17,681,554,755 5450 2,354,3 I,950 7-280 17,139,318,196 5400 2,311,497,650 7-185 16,608,110,615 5350 2,269,086,050 7-090 16,087,820,094 5300 2,227,067,150 6-995 I5,578,334,7H 5250 2,185,440,950 6*900 15,079,542,555 5200 2,144,207,450 6-805 14, 59I.33 1 , 697 56,339,575,889 442,428,177,291 182 New Theories in Astronomy. TABLE VI. continued. Diameters in Miles. Volumes in Cubic Miles. Densities. Volumes at Density of W* let- in Cubic Miles. Observations. 52OO 56,339.575,889 6*805 442,428,177,29! 5150 2,103,366,650 6-7IO I 4 ,II3,5 9 0,222 5IOO 2,052,918,550 6-615 13,646,206,207 5050 2,022,863,150 6-520 13,189,067,738 5OOO 1,983,200,450 6-425 12,742,062,89! 4950 I,943,930450 6-330 12,305,079,748 4900 I, 905. 053,150 6-235 11,878,006,390 4850 1,866,568,550 6* 140 11,460,730,897 4800 1,828,476,650 6-045 11,053,141,349 4750 1,790,777,450 5-950 10,655,125,828 4700 1,753,470,950 5-855 10,266,572,412 4650 1,716,557,150 5-76o 9,887,369,184 4600 1,680,036,050 5-665 9,517,402,223 4550 1,643,907,650 5*570 9,156,565,611 4500 1,608,171,950 5*475 8,804,741,426 4450 1,572,828,950 5-38o 8,461,819,751 4400 1,537,878,650 5-285 8,127,688,665 435 1,503.321,050 5-190 7,802,236,249 4300 1,469,156,150 5-095 7,485.350,584 4250 1,435,383,950 5'ooo 7,176,919,750 4200 1,402,004,450 4*905 6,876,831,827 4150 1,369,017,650 4*810 6,584,974,897 4100 1,336,423,550 4-715 6,301,237,038 4050 1,304,222,150 4-620 6,025,506,333 4000 1,272,413,450 4-525 5,757,670,861 96,451,524,689 671,704,075,372 New Theories in Astronomy. 183 TABLE VI. continued. Diameters in Miles. Volumes in Cubic Miles. Densities. Volumes at Density of Water in Cubic Mile.-,. Observations. 4000 96,451,524,689 4^25 671,704,075,372 3950 1,240,997,450 4*43 5,497,618,693 3900 1,209,974,150 4*335 5,245,237,939 3850 1,179,343,550 4-240 5,000,416,652 3800 1,149,105,650 4*H5 4,763,042,919 3750 1,119,260,450 4*050 4,533,004,823 3700 1,089,807,950 3*955 4,310,190,441 3650 1,060,748,150 3'86o 4,094,487,859 3600 1,032,081,050 3*765 3,885,785,163 3550 1,003,806,650 3*670 3,683,970,405 3500 975>924'95o 3*575 3,488,931,696 3450 948,435.950 3*48o 3.300,557,106 3400 9 2 i,339.65o 3*385 3,118,734,715 3350 894,636,050 3-290 2,943,352,605 33 868,325,150 3*i95 2,774,298,854 3250 842,406,950 3*ioo 2,611,461,545 3200 816,881,450 3*005 2,454,728,757 3*5 791,748,650 2-910 2,303,988,572 "3,596,348,539 735,713,884,116 735,584,493,738 (True half- [ volume 129,390,378 Excess 184 New Theories in Astronomy. CHAPTER X. PAGE 184 Inquiry into the interior construction of the earth continued, 185 Density of 8*8 times that of water still too high for the possible com- pression of the component matter of the earth as known to us. 1 86 Reasons for this conclusion drawn from crushing strains of materials. 187 A limit to density shown thereby. 1 88 The greatest density need not exceed 6 * 24 of water. 189 Gases shut up in the hollow centre. Their weight must so far diminish the conceded maximum of 6*24. 190 Density of inner half of earth at 3000 miles diameter. Greatest density may be less than 5*833 of water. 191 Supposed pressure of inclosed gases very moderate. 193 Meaning of heat limit to density. Temperature of interior half of shell and inclosed gases must be equal. 194 State of the hollow interior. 195 Results of the whole inquiry. INQUIRY INTO THE INTERIOR CONSTRUCTION OF THE EARTH continued. IT may be well to revert here to the experiment we made of putting a cubic foot of rock, of specific gravity 13 '734 in the scale of a balance at the centre of the earth, where we saw that it could not depress the scale one hairbreadth, and make the same experiment by placing a cubic foot of rock of 8' 8 specific gravity in the same scale, at what we have called the region of greatest density of the earth, that is, at 817 miles from its surface. Here, also, we shall find that the scale is not depressed for the very same reason as in the former case, that is because it had nowhere to be depressed to ; and it might be argued that for the same reasons advanced formerly there can be no matter at that place, but the cases are entirely different. In the first case, there is nearly the whole mass of the earth drawing the matter away from the centre were it at liberty to move ; whereas, in the second case, the meeting of the two halves of the shell, at the region where there is the greatest mass of matter, is also the meeting place of the action of New Theories in Astronomy. 185 attraction in its greatest force ; the place to which matter is attracted from all sides, remains stationary, and it is held there both by attraction and weight of superincumbent matter or gravitation. The attraction of the whole earth acts as if it were concentrated at its centre, but that is for external bodies. That kind of attraction on the inner half of the shell would be far inferior to that outwards of the outer half, owing to its greater distance and conflicting nature, and would perturb, as we have said, but not do away with it. The same could not occur at the centre, because it is not the centre of the mass, that is, it is not the place where the greatest quantity of matter existed originally, or is now to be found, and consequently never was, nor can now ever be, the actual centre of interior attraction. It has been said when treating of the earth as being solid to the centre, that it is not easy to comprehend what may be the nature of the rocks we are acquainted with, when com- pressed to one-fourth or one-fifth of their volume, and we do not find ourselves much better off when we contemplate them as reduced to one-third or one-fourth of their bulk, that is, when a cube of one foot is reduced to three or four inches in height, as would be the case with it at a maximum density of 8*8 times that of water when placed at a depth of 817 miles from the surface of the earth. We find, therefore, the idea thrust upon us that there may be a limit to density, perhaps not an absolute limit, but a practical one ; in which case, the greatest density of the earth may not greatly exceed 5*66 times that of water. For, if we conceive that it increases to its maximum at 100 miles from the surface, and continues nearly uniform thereafter, a little calculation will show that the greatest density of the outer half of the shell need not much exceed 6 times that of water ; and, of course, the same will be the case with the inner half should its density be almost uni- form till 100 miles from the inner surface is reached. It might even so happen that at a depth of 25 to 30 miles the practical limit might be reached ; for a column of granite of one foot square and 25 miles high would weigh, and exert a pressure upon its base of 10.000 tons, a pressure equal to nearly fifteen times what would be sufficient to crush it into powder ; in which i36 New Theories in Astronomy. case the greatest density of the earth might not much exceed the 5 * 66 that we are accustomed to think of without thinking. It may be deemed absurd to think that there is even a practical limit to the density of matter, but on the other hand it is much more absurd to suppose that there is not an absolute limit to it. We cannot conceive of density being other than the result of compression, and we cannot believe that matter can be compressed more and more continually for ever. There must be some end to compression. Perhaps it was the difficulty in conceiving of rock being compressed to so small a fraction of its volume as would enable it to take its place at the centre of the earth where it has been said that, " it must weigh like lead " that originated the idea of its centre being occupied by the metals, arranged as they would be in a rack in a store, the heaviest pieces at the bottom of the rack, and the lighter ones higher up. When fairly looked at, density would really seem to have a limit, except in so far as it may be combined with heat. We know that water is compressed 0*00005 part of its volume for every atmosphere of pressure to which it is sub- jected. But 0-00005 f r round numbers, is in fractional numbers 20 ^ 00 ; therefore a pressure of 20,000 atmospheres would compress a cubic foot of water into 2Q * QO of a foot in height, or practically into nothing. We know, also, that as a column of water 33 '92 feet high balances one atmosphere, one mile in height will be equal to 155*66 atmospheres, and 20,000 atmospheres will produce a pressure equal to a column of water 128 miles high ; therefore, a cubic foot of water, subjected to such a pressure, would be compressed into virtually nothing. Again, supposing that we have a column of liquid rock, of 2j times the density of water, of the same height of 128 miles, we should have a pressure of 2j times that of the column of water ; and as we have no reason to believe that granite in a liquid state has to obey a different law of compression to the one obeyed by liquid ice ; then a column of granite 5 1 miles high would be sufficient to squeeze its own base, not only off the face of the earth but out of the bowels thereof. It will be seen, therefore, that at 100 miles New Theories in Astronomy. 187 deep from the surface, the density of the earth might well be equal to not only 5 66 times the density of water but to a great deal more ; and that our estimate of 3 times the density of water, at 9 miles deep, was far within the mark. The authors of text-books on the strength of materials tell us that " the Modulus of Elasticity of any material, is the force that would lengthen a bar of that material of I inch square to double its length, or compress it till its length became zero ; supposing it possible to stretch or compress the bar to this extent before breaking." This is neither more nor less than a counterpart of the law of gases, upon which the air thermometer is constructed, applied to solid matter, and may be used in the same manner. But we can never produce a perfect vacuum, and so annihilate a gas and temperature ; neither can we annihilate matter, nor easily reduce it to one half of its volume. Now, we have seen, a little way back, that a column of granite 25 miles high would exert a pressure at its base 1 5 times as great as would crush it to pieces ; so that a column of 25 -f- 15, or I '66 miles high would destroy the elasticity of the material, because, when crushing takes place, all elasticity is gone. We cannot, there- force, get much satisfaction out of any calculations made upon the theory of the strength of materials ; still, by them, we can make more plain the absurdity of any notion of the indefinite compressibility of matter. But if, in the face of contravening its conditions, we follow the reasoning used for the formation of the theory, and take the modulus of elasticity for granite as 2,360,000 feet, then the same modulus would compress a bar of granite of I inch square in section till its height became zero. And as that length is equal to 447 miles, at that depth from the surface of the earth, granite or any other rock or stone of a similar nature would be compressed out of existence by the weight of the superincumbent matter. Thus we have arrived at two measures of force which would compress to zero the rocks that are known upon the earth. One where rocks are looked upon as in a molten, liquid state, and analogous to water, where the force is equal to that exerted by a column of the material 51 miles high ; T 88 New Theories in Astronomy. and the other where the column requires to be 447 miles high. In either case the same method of calculation will show that columns one-half of these heights, will compress the material into at least one-half of its volume that is half-way between what it is at the surface and would be at the specified depths and consequently into double its density. So we find in the one case that the density of the earth ought to be about 5 '66 times that of water at a depth of 25 J miles ; and, in the other, at somewhere less than 225 miles deep. But, before proceeding to use and reason upon these depths, we must recall to mind that the calculations from which we have derived them, in the second case, have been made in violation of the theory that was adduced for the purpose, and that in consequence the latter depth must be excessive. For, were we to erect a structure of any kind, calculating the stresses it would have to bear, under the same violation of the theory, we should inevitably find that the structure would give way under the strains that would be brought upon it ; that is the columns 25^ and 225 miles high would compress the same kind of matter composing them into very far below one- half of its volume. This premised, let us go back to our layers of 25 miles thick with their respective volumes. Nine of them counted from the diameter of 7900 miles inwards, will be equal to 225 miles and will bring us to 234 miles deep, which at the same time that it leaves us the same volume and mass that we have always retained for the first 9 miles in depth, will facilitate our calculations considerably without making any appreciable difference in them. We shall then have to find for the 9 layers 9 corresponding densities increasing from 3 to 5 -66, and if we multiply these together respectively, and add the numbers of the volumes and masses of the outer 9 miles in depth, we shall get, at the diameter of 7450 miles, a simple volume of 43418,587,327 cubic miles, and mass volume of 195,312,523,450 cubic miles. Deducting this latter sum from 735>584,493,738 cubic miles, which represents the half mass of the earth at the density of water, we have a remainder of 540,272,970,288 cubic miles. On the other hand we find that New Theories in Astronomy. 189 the simple volume of the earth comprehended between the diameters of 7450 and 6284-5 miles is 86,543,337,361 cubic miles ; so that if we divide 540,272,970,288 by this sum, we find that a density of 6*24 times that of water over the whole intervening space between the two diameters just cited will make up the whole half-volume, at the density of water, from the surface of the earth to the diameter of 6284-5 miles. Then, for the inner half-mass : If we multiply the simple volume between the diameters of 6284-5 miles, and 3150 miles, which is 113,596,348539 cubic miles by 6-24, we get 708,841,214,870 cubic miles at density of water ; and if from there we run down the density to 3 at 2700 miles in diameter we get 27,400,652,354 cubic miles, which added to the last mentioned amount gives 736,241,867,224 cubic miles, some- what in excess of the inner half-mass of the earth at density of water. Thus we see that in order that the average density of the earth of 5 * 66 may be made up, there is no necessity for appealing to matter of any kind with a density of more than 6*24 times of water. And there is still some- thing else of importance to be taken into consideration before we can bind ourselves to a density even so great as that. We have said, a few pages back, that there can now be no undeposited cosmic matter in the interior of the hollow earth, and that as far as such matter is concerned the hollow part may be a perfect vacuum. This is not absolutely true, for gases may be cosmic matter, just the same as any others of the elements out of which the earth is formed, but what is generally meant by cosmic matter is solid at least, we have always looked upon it in that light and all solid matter must have been deposited upon the interior surface at an im- measurably long period of time before the nebula forming the earth came to have even the density of water ; certainly before it came to be in a molten liquid state ; and we did not want to introduce any posterior evolutions in order not to complicate our calculations, and also to obtain some tangible bases to which the consequences of these evolutions might be applied. But as we have now both form and density to work upon we may take them into account, and it will be found New Theories in Astronomy. that neither of these two bases will be very materially altered by them. When the earth was in a molten liquid state, it is believed as we have said on a former occasion to have been sur- rounded by a dense atmosphere, composed of gases and vapours of metals, metalloids, and water, and we have no reason to doubt that the hollow of the sphere was filled with a similar atmosphere, only the vapour of water would, most probably, be dissociated into its elements of oxygen and hydrogen. Also we have every reason to believe that even at the present day gases are being produced in the interior, one part of which find their way to the surface and are dissipated into the atmosphere in the same manner as the gases from the chimney of a furnace ; and another part into the interior, where they could not escape but would be stored up in the hollow. Thus at the present day there may be an atmosphere there, composed near the surface of vapours of the elements with gases above them, so to speak, at a very high degree of pressure. These gases could riot have gone on accumulating always, but must have found an exit in some particular place, or places, when the pressure exceeded the resistance, or when this was diminished by some convulsion such as an earth- quake ; but we do not want to define too much, or make more suppositions on this point than what present themselves to us in a reasonable way. All that we need say is, that the resist- ing power of some thousands of miles of solid, or even viscous, matter must be enormous, and the pressure necessary to force its way through it must have been equal to many thousands of atmospheres. We know that a pressure of 773*4 atmos- pheres condenses air to the density of water, and it must be the same with any similar gas ; so we have only to suppose that the pressure is 4827 atmospheres which is equal to 773*4 multiplied by 6*24 in order to bring the whole of the gases, and vapours of elements, in the hollow to the same density of 6*24 times that of water, which we have shown need not be exceeded in any part of the earth. And such being the case, we can place the division between solid and gasiform matter in any point of the radius that may seem to New Theories in Astronomy. 191 us reasonable, only we must always have as much solid matter in the inner as in the outer half-mass of the earth. Following nearly the result we have obtained in another way, by placing the division of the hollow part at 3000 miles in diameter, the volume of which is 14,137,200,000 cubic miles, and multiplying this by 6*24, we get a mass equal to 88, 2 1 6, 1 28,000 cubic miles at density of water, composed of vaporous and gaseous matter in the hollow centre, and conse- quently much greater than is required to make up the total mass of the earth at the density of water ; which shows that the density of the mass between the diameters of 7450 and 3000 miles must be less than 6*24 times that of water. How much less is very easily found, by dividing the surplus of 88,216,128,000 cubic miles over the whole volume between 7450 miles in diameter and the centre, because in this way we shall include the whole mass arising from both solid and gasiform matter. This whole volume that of a globe 7450 miles in diameter is 216,505,262,050 cubic miles, which, divided by the surplus gives the amount o * 407 as the density to be deducted from 6 24 on its account, and therefore the greatest density of any part of the earth need not be over 5 833 times that of water. This result derived from our operations will be acknow- ledged, we doubt not, to be much more satisfactory, we might say, more comprehensible, than to have to believe that our known rocks and stones could be compressed till they were J 3 '734 or even 8 8 times heavier than water. At first sight 4827, say 5000, atmospheres or 75,000 Ib. on the square inch, appears to be an enormous pressure, but it is nearly almost as nothing compared to the pressures we have been dealing with. A column of granite I mile high would exert a pressure upon its base of 6050 Ib. per square inch, and one of 25 miles high of 151,200 Ib., or double the number of atmospheres we have applied to the gases in the hollow of the earth. If we take a column 225 miles high, such as we considered to be the least that would be necessary to compress granite into one-half of its volume, we get 1.360,860 Ib. per square inch, or over 90,000 atmospheres of 1 92 New Theories in Astronomy. pressure ; and if we go into thinking of columns of 447 and 817 miles this last being the depth from the surface of the division of the matter of the earth into two equal portions we could have gases compressed to 174,600 and 326,700 atmo- spheres or, dividing the numbers by 773 '-4, 222 and 422 times the density of water ; so there is no cause to stumble over high pressure. With even 10,000 atmospheres, more than double the number assumed, we should have gases as heavy as the material we found at the centre of the earth, when we were looking upon it as solid to the centre which was 13 '734 times the density of water and so get rid of burying the precious metals where they would be " matter in the wrong place," and according to D'Israeli's definition, justly entitled to the epithet applied to them, sometimes, by people who have never been blessed with a superabundant supply of them. At the same time, we find out what we knew before, viz. that we may have gases heavier than the heaviest metals and as rigid as steel, if we can only find a vessel strong enough to com- press them in, along with the means of doing it ; and also that the thousands of miles of highly compressed matter, between the hollow centre and the surface of the earth, are far more than sufficient to imprison gases of far, very far, greater elasticity than our modest measure of 5000 atmo- spheres. And we hope to be able to show presently good reason for believing that the gases compressed in the hollow, at what may really be considered as very high pressures, have had, and may probably still have, a very important part to play in the evolution of the earth. We have just seen that the pressure produced by a column of granite I mile high would be 6050 Ib. per square inch, consequently one of double the height, or 2 miles, would exert a pressure of 12,100 Ib. per square inch at its base, equal to the crushing strain of the very strongest granite we know, while at the same time that strain would not amount to one-sixth of 4827 atmospheres ; so that if the gases in the hollow of the earth were at a pressure of only 800 atmo- spheres, their pressures would be able to crush granite of that class to pieces, and therefore the estimate of specific gravity New Theories in Astronomy. 193 of 3 for the density of the interior surface which we made at the beginning of our calculations for the hollow sphere cannot be looked upon as by any means exaggerated. We might now reform our calculations of the two halves of the interior of the earth, giving a more rational and curve- like form to the densities, under the supposition that at much less distance than 234 miles from the surface, matter might be compressed to its utmost limit ; but as, according to our demonstration, the solid matter of the earth must have been divided into two equal parts at the place where the greatest mass was, long before it could have been condensed into a state to compress gases ; and as the total mass of solid matter must, in order to make up the total mass of the earth, depend; to some extent on the mass of imprisoned gases; we are unable to make any reform much different to what our calculations show. Besides, as the difference between average densities of 5 * 66 and 5 '67 makes a difference of 2,600,000,000 cubic miles on the mass of the earth reduced to the density of water, very approximate accuracy cannot be attained in any calculations. What is meant by a limit to density except in so far as it is combined with heat, is that whatever density may be given; to matter by compression when, it is in a heated state, a greater density will be found in it when it is deprived of that heat ; that whatever may be the density of any part of the interior of the earth in its present state, that density will be increased when the earth becomes cooled down to the tem- perature derived from the heat of the sun, or to absolute zero of temperature, if such there be, on account of shrinking in cooling ; and that therefore there can be no absolute limit to density as long as there is any heat in matter. It may not be unnecessary for us to recognise now that the weight of a column of granite would decrease as the depth increased, for the force of gravitation would be diminished by having a part of the attraction of the earth above instead of below it ; but at 100 miles in depth the diminution would be only about one-eighth if distance is taken into account of the 817 miles down to the plane of greatest density, and o 194 New Theories in Astronomy. P art tf tne mass l e ft above is considered ; differences that would make extremely little alteration on our calcula- tions. It will not be out of place either to take a look at what may be the temperature of the interior of the shell, and of the gases shut up in the hollow part of the earth ; and we have not much to say on the subject, because we shall not depart from the system we have followed up till now, with consider- able strictness, of not theorising or speculating on what may be ; but will restrict our observations to theories that have been very generally adopted by astronomers, geologists, and scientists in general. The air thermometer will be of no use to us, for whatever may have been the temperature when the earth was in the process of formation, it must have diminished very greatly during the cooling process it has undergone since, and we know that gases heated in a closed vessel in such manner that pressure and temperature will agree to the theory on which the air thermometer is constructed, may be cooled down afterwards to almost any degree required, and the relation between temperature and pressure destroyed thereby. At one time it was thought that the earth had only a solid crust, and that, under it, the whole of the interior was in a molten liquid state. Then some physicists thought that, through pressure of superincumbent matter, solidification must have begun at the centre ; others that it began almost simultaneously at the surface and centre, and that there may still be a liquid mass between the two solidifications this is repeating what we have said before, but it is done only to bring it to mind. We, at present at least, do not want to have anything to do with any of these theories, only we believe that we have shown in an indisputable manner that there could be no solidification at the centre, because there could be no matter there capable of being solidified gases could not be solidified under such pressure, and at all events heat, as there must have been there. We believe at the same time that no one will deny that the heat of the earth increases as the centre is approached, and that the temperature of the interior may be very great. The crust of the earth was at New Theories in Astronomy. 195 one time supposed to be only 25 to 30 miles thick, because the increase of heat at that depth would be sufficient to melt any of the substances we are acquainted with on the surface repetition again ; but for many years past it has been deemed necessary to increase the thickness to even hundreds of miles, for reasons some of which will be alluded to in due time ; and if, even at these depths, the increase of heat were only sufficient to fuse all the substances we know, it is very certain that at the interior surface of the shell it must be very much greater, as heat from there could only be conducted outwards, and the difference required to cause conduction, of any considerable degree of activity, through more than 2000 miles must be enormous, according to the experiments made by various physicists upon metals, which have a very much higher conducting power than rocks, and especially strata, of any kind. Therefore there can be no doubt, we think, that the inner surface of the shell must be at a very much higher temperature than what would preserve it in its liquid state, and that the matter composing it is liquid to a depth where it might be solidified by the pressure of superincumbent matter. We do not see how convection currents could be instituted, much less kept up, in melted matter, under the viscosity, and, at least quasi-solidity, sure to be produced by pressure of tens of thousands of pounds on the square inch, and therefore we do not take them into account. Any way, whatever may be the temperature of the interior surface of the shell, the same must be that of the imprisoned gases, because there convection currents could and must exist were they even only created by the rotation of the earth and attrac- tion of the moon and cannot fail to keep the whole of the hollow part at the same temperature. It would be absurd to suppose that these gases could be at a lower temperature than the upper layers, counted from the region of greatest density, of the interior surface of the shell. This section of our work may now be brought to a close by stating the conclusions at which we have arrived, leaving the results involved by them to be discussed separately, which we shall proceed to do immediately without binding ourselves O 2 196 New Theories in Astronomy. so strictly, as we have done hitherto, to the avoidance of anything that may be looked upon as theorising or specu- lating. We believe we have conducted our operations in the most strict conformity to the law of attraction, and have no doubts whatever about the form of the interior of the earth resulting from them ; but there may be some room for small variations in the details of the various densities, and the position of the interior surface of the shell, arising from the pressure of the gases in the hollow centre, and the weight they will, in consequence, add to the general mass of the earth. The conclusions are as follows : (1) That the earth is not solid to the centre, nor is it pos- sible that it could be, according to the law of attraction, but is a hollow sphere. (2) That its greatest density must be at the region where the greatest mass of matter is to be found as must have been always the case from the time it was a globe revolving on its axis, whether gasiform, liquid, or solid which is now at 817 miles deep from the surface ; and that the greatest density may not be much more than the mean of 5 '66 times that of water ascribed to it by astronomers. (3) That the inner surface of the shell of the hollow globe cannot be much over or under 2000 to 2200 miles from the outer surface. (4) That the hollow part of the globe must be filled by an atmosphere consisting possibly in part of vapours of the chemical elements, and by gases at a very high degree of pressure. (5) That the region of greatest density, and the position of the interior surface of the shell, may be expressed with very approximate accuracy as follows : The former must be at '7939 f tne mean radius of the earth, and the latter at 0*5479 of the same ; both counted from the centre. (6) That if the earth is a hollow sphere, the same must be the case with all the major planets and their satellites, the sun, and all the suns, or stars, that are seen in the heavens ; and that their interior proportions and form must be in much the same ratios to their radii as those we have found for the earth. New Theories in Astronomy. 197 CHAPTER XL PAGE 197 The Earth. The idea entertained by some celebrated men, and others. 199 Difficulties of forming a sphere out of a lens-shaped nebula. 200 Various studies of the earth's interior made for special purposes. Difficulty some people find in conceiving how the average density of little over 5 '66 can be possible, the earth being a hollow sphere. 201 What is gained by its being a hollow shell. 202 Geological theories of the interior discussed. Volcanoes and earth- quakes in relation to the interior. 206 Liquid matter on the interior surface of the shell, and gases in the hollow, better means for eruptions than magma layers. 207 Focal depths of earthquakes within reach of water, but not of lavas. 209 Minute vesicles in granite filled with gases, oxygen and hydrogen, but not water. 211 The Moon. A small edition of the earth. 212 Rotation stopped. Convulsions and cataclysms caused thereby. Air, water, vapour driven off thereby to far off hemisphere. Liquid matter in hollow interior would gravitate to the inside of the nearest hemisphere. 213 Form and dimensions during rotation. Altered form after it stopped. 214 Agreeing very closely with Hansen's "curious theory." CONSEQUENCES OF THE EARTH AND MOON BEING HOLLOW BODIES. The Earth. The idea that bodies such as those of the solar system, even of the whole universe, have their greatest density where the greatest mass is and are hollow spheres, is so natural and logical, more especially if it is supposed that they have all been formed out of some kind of nebulae, that it seems strange it has never been brought forward prominently before. We say prominently because we know that the earth has been considered to be a hollow sphere by very eminent men, such as Kepler, Halley, Sir John Leslie, and by others of less I9& New Theories in Astronomy. name long after them. In support of this last remark, we shall make a few extracts with comment on them from an article on the " Interior of the Earth " in " Chambers's Journal" for February 1882, which have some interest in connection with our work. 1. " The great astronomer Kepler, for instance, in seeking to account for the ebb and flow of the ocean tides, depicted the earth as a living monster, the earth animal, whose whale- like mode of breathing occasioned the rise and fall of the ocean in recurring periods of sleeping and waking, dependent on solar time. He even, in his flights of fancy, attributed to the earth animal the possession of a soul having the faculties of memory and imagination." If it could be believed that Kepler had any idea of the earth being formed out of a nebula, whether hollow, or solid to the centre, the idea of a breathing animal was almost a con- sequence, because the attraction a thing he is supposed to have known nothing about of the original nebula for the earth one, on matter so light as nebulous matter, would raise enormous tides and make the earth, in its then state, not far from like an enormous primitive bellows made out of goat- skins. No one knows what dreams may have passed through his brain. The last part of his notion was altogether fanciful. 2. " Halley was opposed to the idea of the globe being solid, ' regarding it as more worthy of the Creator that the earth, like a house of several storeys, should be inhabited both without and within.' For light, too, in the hollow sphere, he thought provision might in some measure be contrived." This notion appears to be altogether fanciful, the fruit of an en- thusiastic, exuberant imagination, leaving no trace of scientific thought upon the subject. 3. " Sir John Leslie, like Halley, conceived the nucleus of the world to be a hollow sphere, but thought it filled, not with inhabitants, but with an assumed * imponderable matter having an enormous force of expansion.' " It would be inter- esting to know on what bases he formed his ideas, as the filling of the hollow with imponderable matter seems to show more method than the former cases, but we have never seen New Theories in Astronomy. 199 any allusion made to his theory anywhere, except in the article we are quoting from. There may have been some reasons given for such a supposition in his " Natural Philo- sophy," but when we began to read that work in times long past, a more modern one was recommended to us, and we lost the chance, never to return. There are other theories referred to in the article, but we shall take notice of one more only. 4. " A certain Captain Symmes, who lived in the present century, was strongly convinced of the truth of Leslie's theory. He held that near the North Pole, whence the polar light emanates, was an enormous opening, though which a descent might be made into the hollow sphere, and sent frequent and pressing invitations to A. von Humboldt and Sir Humphrey Davy to undertake this subterranean expedition ! But these imaginative conceptions must one and all be set aside, and the subject treated on more prosaic, though not less interest- ing, lines." This conception of Captain Symmes will probably be looked upon as the most absurd of the whole lot, but to us it seems to give evidence of more thought than any one of them. One would think that he must have formed some notion of how a hollow sphere, with an opening out to the surface at each one of its two poles, could be formed. We must note that he lived in, possibly after, the time of Lap- lace. We doubt whether anyone has ever studied out thoroughly how even a solid sphere could be ultimately elaborated from a nebula. It has always been a very general idea that a con- densing and contracting nebula would, under the areolar law, assume the form of a lens rather than of a sphere. If this be so in reality, we may ask : How can the law of attraction produce a sphere out of a lens-shaped mass of rotating vaporous or liquid matter ? It seems evident that to bring about such a result attraction must cease to act altogether in the polar directions, and only continue to draw in the matter from the equatorial directions of the lens, till the desired sphere was formed ; and, How were the action and inaction 2OO New Theories in Astronomy. of the law of attraction to be regulated meanwhile ? Or, when the time came that a sphere of a pre-arranged diameter could be formed, a goodly part of the lens must have been cut off and abandoned ; in which case we have again to ask : What was done with the surplus, the cuttings ? No doubt they could be used up in meteor swarms, comets, or some- thing ; but Captain Symmes's theory has opened up a field for a good deal of thought, and our present knowledge of polar matters prevents us from being sure that strange discoveries may not be made as to the condition of the earth at the poles, although there may not actually be holes into the hollow interior. With regard to the last sentence of the quotation, we fully agree and are doing our best to comply with it. And in so doing, we shall have to return to the formation of globes out of nebulae, elaborated into something more advanced than even lens-shaped discs. There is no doubt that the reasons assigned by most, if not all, of the authors of the notions above cited are very fanciful, but one can hardly believe that the true reason why the earth must be hollow-- has not occurred to some of them ; and that they did not follow it out because it involved too much work, and they did not feel inclined to undertake it, or had not time. On the other hand, modern astronomers and physicists have been so fascinated by the discoveries they have made, and in following them up, that the temptation to go on in the same course has been too great to allow them to spend time on the investigation of sublunary and subterranean affairs. Some of them have indeed studied the interior of the earth for special purposes, such as the thickness of the crust, solidity or liquidity, stability, precession of the equinoxes, the action of volcanoes, etc., etc. ; but they never, apparently, exa- mined into any of these features to the very end, otherwise, we believe, they would have come long ago to the same conclu- sion as we have. And withal it seems wonderful how near some of them have come to it. To most people it would appear absurd to think that any part of the earth of any great magnitude can be hollow, if in order to make up its mass its average specific gravity must be 5 '66 more especially, if we New Theories in Astronomy. 201 tell them that the greatest specific gravity at any place need hardly exceed 5 '66 forgetting that weight or mass can be taken from the interior where the volume per mile in diameter is small, and be distributed near the exterior where the volume per mile in diameter is comparatively immensely greater. But in whatever light we look upon the conclusions we have arrived at, a change in the construction of the bodies in space from solid to hollow spheres must produce changes in our ideas of them, and have consequences of great importance, too numerous to be all taken account of ; we shall, therefore, only take notice of the most prominent. Looking at the earth as a hollow sphere, we get rid of the difficulty of conceiving that matter can be compressed to three or four times less than the volume it has as known to us ; and also of the misplacement of metals to the incredible degree we have shown to be necessary to make up its whole mass according to the sorting-out theory. And if we can only be bold enough to look upon gases as ponderable matter that can be compressed to great density, and so added to the weight of the whole mass, we may riot be under the necessity of compressing the known matter composing it to even the half of its volume. Somewhere in the first quarter of this century (see " Edin- burgh Review," January 1870) Mr. Hopkins argued that the solid crust of the earth must be at least 800 to 1000 miles thick, in order to account for the precession of the equinoxes and nutation, but about a quarter of a century afterwards M. Delaunay demonstrated before the French Academy by actual experiment that the thickness of the crust had no bearing whatever on the problem. And about the same time Lord Kelvin inferred from the same thickness of crust that " no continuous liquid vesicle at all approaching to the dimensions of a spheroid 6000 miles in diameter could possibly exist in the earth's interior without rendering the phenomena of precession and nutation sensibly different from what they are " ; and that the earth, as a whole, must be far more rigid than glass and probably more rigid than steel, " while the interior must be on the whole more rigid, probably 2O2 New Theories in Astronomy. many times more rigid, than the upper crust." With the theory of a hollow shell, a better foundation is given for Mr. Hopkins's argument than a solid crust at about the same depth as he assumed, while at the same time the liquid vesicle of 6000 miles in diameter is removed, which Lord Kelvin showed would change the phenomena of precession and nutation. We have seen that imprisoned gases may have a high degree of density, and consequently rigidity, and may in some measure supply what was required by Lord Kelvin, who knows, also, very well that a structure with some degree of elasticity in it is stronger than one that is absolutely rigid. Moreover, the shell of the earth, composed of solid materials at a very high temperature, and consequently so far plastic, could not fail to accommodate itself to any variation of centri- fugal force that could take place. Variations in rotation of the earth could only have come on extremely slowly, and even the most rigid matter we know will gradually yield to extreme pressure long continued. But this subject of the plasticity of the most solid part of the interior was discussed and, it may be said, demonstrated during the meeting of the British Association of 1886, as reported in "Nature" from July to September of that year. Any way, the possi- bility of plasticity is most patently shown by the hollow- sphere construction of the earth. We do not know what were M. Delaunay's proofs that the thickness of the crust has no bearing whatever on precession and nutation, but if they were complicated with the fluidity, or even viscosity, of a liquid interior beyond a depth of 800 to 1000 miles, they must be entirely changed under the notion of a hollow sphere where there could be no really liquid molten matter, except near the inner surface. One thing we may be certain of, and that is, there must be something to account for precession and nutation, and we believe that the hollow shell, with the greatest density where the mass is greatest, is a much more rational cause for these phenomena than the bulging out of the earth to the extent of 1 3 miles or so at the equator. It is very difficult to find out what geologists consider to be the nature of the interior of the earth in its details, but for New Theories in Astronomy. 203 our purpose no particular knowledge is required. However, it is necessary to allude to the principal features of their theories in order to note and remark how far they will agree to, or be facilitated, or the reverse, when applied to a hollow sphere. It would seem that almost all geologists are agreed that the central part is solid, and possibly extremely rigid owing to the enormous pressure of superincumbent matter ; that it has a solid crust of several hundreds of miles in thickness ; and that under this there is a sub-crust divided into two or more layers of different densities, partially liquid or at all events plastic, extending all over the solid interior matter ; the chief purpose for which it is required being apparently to supply matter for volcanic action and surface movements. Under the theory we are advocating, the place of greatest density of the interior is calculated to be at 817 miles from the surface, and its greatest approach to solidity will be there also ; consequently, if geologists consider that it will have sufficient plasticity there to provide matter for volcanic eruptions, they will be at one with us so far. But should they consider that they require, for volcanoes, matter more liquid than is likely to be found at that depth, they will have to place their magma layers either much deeper or somewhere between that depth and the surface, in which case they will encroach on the requirements of astronomers, without liber- ating themselves from a difficulty in which they must find themselves involved under their present ideas. They say that these plastic layers exist under the solid crust all round the interior of the earth, so that if one of the duties they have to perform is to keep the various chains of volcanoes in com- munication with each other, their lateral movements must extend to some hundreds of miles in the cases of the enormous volumes of matter that are sometimes thrown out in even modern eruptions, and they have to provide the means for procuring that lateral motion. Shrinkage from cooling, or falling in of part of the solid crust, might bring about these enormous outbursts of lava, but they would be more likely to produce simple overflows than the explosive ejection of such 2O4 New Theories in Astronomy. masses as are now being recorded from time to time. We have brought into remembrance, page 148, that water cannot penetrate into the interior of the earth to a greater depth than 9 miles, more or less, as water, and that beyond that depth it can only exist in the form of steam, or dissociated into its elements of hydrogen and oxygen. As long as it continued in the form of water it could be suddenly flashed into steam, of not far from two thousand times its volume, by relief from pressure or sudden application of heat, and thus be converted into a violent explosive almost instantaneously ; but when it came to have the form of a gas, it could only be 'heated gradually the same as any other gas. It is clear, therefore, that water cannot be looked to for producing the force, explosive or otherwise, that is required to raise even molten matter from depths of hundreds of miles to overflow from the summits or outlets of volcanoes. A pressure of 400 atmospheres would be required to balance a column of average rock of one mile high. A mass of water, through shrinkage of the crust, might get introduced to the vent of a volcano, or some cavity connected with it, a few miles under the surface of the earth and cause an earth- quake it might be introduced by an earthquake or eruption or both, abundantly formidable and destructive, no doubt, but only comparatively superficial, such as those of Naples and Charleston, where the extreme depth was calculated to be only a few miles ; but it seems to us to be totally inadequate to produce those outpours that last for days and weeks, covering leagues of land, and filling up b^ys of the sea, with floods of lavas. It may be the principal agent or ally in producing the horrors and devastation of a grand eruption that has invaded the regions of water, but it is not to be conceived as possible that it can be the prime cause. The volumes of steam, water, and mud thrown out on such occa- sions, only tend to distract our attention from looking deeper for the true cause of the eruption. Geologists are therefore thrown back upon their magma layers to look for the motive power for producing these grand eruptions, and they cannot get water down deep enough to do it. New Theories in Astronomy. 205. Tides produced by the sun and moon cannot be appealed to, otherwise the eruptions would be more or less uniform in their periods of occurrence. Sudden evolution of gases in the magma layers could not be accounted for in any way known to us, and accumulation of gases would involve the idea of immense cavities, to serve as reservoirs to be gradually filled till the pressure was sufficient to force a way out, and would imply a formation of the interior in compartments specially adapted for particular purposes, and altogether too fanciful to be entertained. Where could such enormous masses of matter, as those thrown out, come from at only a few miles from the surface ? The great eruption at the Sandwich Islands, of about a century ago, after flowing over a distance of many miles of land, on which it left enormous quantities of lava, filled up a bay of the sea twenty miles long, and ran out a promontory of three or four miles into the sea ; and we cannot conceive it to be possible that such a quantity of matter could be blown out from something less than 9 miles deep by water suddenly flashed into steam. The critical temperature of water that temperature at which it changes into steam under any pressure however great being 412, its pressure in the state of steam will be some- where about 7150 Ib. per square inch, let us say 500 atmo- spheres ; then, if 400 atmospheres are required to balance I mile in depth of average rock, as we have stated above, the pressure of steam just cited would balance only ij miles of rock. We can, therefore, see how inadequate it would be to force a column of lava up from even the depth of 9 miles. At that depth 3600 atmospheres of pressure are required to balance a column of lava, and there are only 500 available. It has been said that the downward pressure of steam would force up the lava through the vent of a volcano, but an ar- rangement of that kind would require a downcast shaft as well as the upcast one of the vent like as there are in col- lieries ; but the downcast would have to go very deep to com- press the steam a gas now to the required number of atmospheres. Far more likely that the steam itself would put an end to any increase of water, by driving it back 206 New Theories in Astronomy. through the channels by which it was descending ; for if they are supposed to exist under a solid crust of 800 miles thick the pressure required would be 320,000 atmospheres, and with a crust of only 100 miles thick 40,000 would be required. The only way, therefore, in which volcanic eruptions can be produced in the earth, if solid or liquid, or partially solid and partially liquid, to the centre in other words, from magma layers is by the shrinking of the crust squeezing out the lava. With a hollow earth and shell of more or less 2200 miles in thickness, liquid to some depth on the interior surface the difficulty becomes very much less. The communication between the vents of volcanoes would be complete and simple, without any lateral forcing of the lava through magma layers made expressly for the purpose ; it would be an open and natural flow from one place to another. That there are such volcano vents connected with each other has been very generally believed, and even almost proved by observation of eruptions taking place in two or more almost simultaneously, or at the least showing signs of violent agitation, the motive forces for which would be the gases which we have concluded must be imprisoned in the hollow centre. When their pres- sure came to be sufficient to blow or force out the liquid, or semiliquid matter, bubbling and boiling in the vents in constant activity, there would be an eruption, during and after which the gases would escape till their pressure was greatly reduced, when the volcanoes would return to their semi-active state. The gases would naturally be those of the many kinds that are found in eruptions, by reason of their being generated in the earth, mixed with steam and water in the manner we have already shown. Let it not be supposed that the gases would require to have force enough to raise lavas from depths of over 2000 miles from the surface. According to our arguments for a hollow earth, at 817 miles from the surface the two halves outer and inner of the matter composing it meet and balance each other, so that all the pressure required would be what is necessary to overcome the inertia, viscosity, or co- hesion of the matter in the vents. What that would be we New Theories in Astronomy. 207 do not pretend to be able to calculate, but we believe that it would be very much inferior to that required to balance a column of lava of even 100 miles high. We have seen that gas compressed to 4835 atmospheres would be 6 times more dense than water, and of equal specific gravity to the heaviest matter required in any part of the earth to make up its average density to 5 '66 that of water, and we cannot assume any greater pressure than this, without diminishing that maximum. If that, or any lesser degree of compression, would supply the necessary force, then all difficulty is removed further than pointing out the means of keeping the volcano vents open or openable ; and the quality of openable may be facilitated by the contraction of the interior from cooling. If a greater pressure be necessary, we need not be afraid of greatly increasing it, for the only consequence would be to diminish the maximum density of solid matter required in any part of the earth, to make up the general average to 5 '66, which means less compression of the matter. If the idea of the accumulation of gases in the hollow centre, or of the hollow centre itself, is inadmissible, then scientists in general can continue as before with their magma layers aqueo- igneous if they like but they must abandon the notion of lavas being expelled from them by steam pressure. We repeat that steam could never get down in the form of steam to the depths they require. The temperature there would be more than sufficient to resolve it into its elements of oxygen and hydrogen, and it would behave very much like the gases we have supposed to be in the hollow ; there might be accu- mulation, but there could be no sudden flashing into existence like steam from water. In support of our observation if it needs support that water as water cannot penetrate into the earth to a greater depth than where it meets a temperature of 412, we may refer to reports on earthquakes of comparatively recent occur- rence. We learn from the "" London Quarterly Review " 'of January 1869, that in the Neapolitan earthquake of 1857, Mr. Mallett found the greatest focal depth to have been 8J geo- graphical, or 9-35 statute miles, which agrees very well with 208 New Theories in Astronomy. the depth to which water could penetrate and be suddenly flashed into steam. (We say nothing, for the present at least, about how the water and the heat managed to meet so instan- taneously.) The shock of the instantaneous generation of steam might be felt much lower, but it would tend to inter- rupt, not to produce, the eruption of lavas. In speaking of the pressure on the walls of the cavity, where the shock was produced, being 640,528 millions of tons, the reviewer says, "it may have been greater because the steam might be supposed to have acquired the temperature of the lava," and that is 2000 F. ; but that could not well be. In order to meet lava of that temperature the steam would have to descend to from 20 to 25 miles deep ; on the other hand, if the lava is assumed to have entered the cavity, it could only do so at a comparatively low velocity and would not reach more than a fraction of the steam at a time, and even for that reason there could be no flashing, as steam is only a gas, and cannot be heated otherwise than as a gas. Here the spirit of facilitating the meeting of the lava and the steam, is as apparent as in bringing about the meeting of the water and the lava noticed above. On the whole, therefore, we think that we were right in saying that steam or water cannot be the cause of volcanic eruptions, but that the invasion of the domains of water by the lavas may be the cause, in the main, of the explosive part of eruptions, and of the most disastrous effects of earthquakes. Moreover, the focus of the Neapolitan earthquake was 75 miles distant from Vesuvius, and therefore far removed from anything like direct connection with the vent of the volcano, so that water from it in any form could have no effect upon the magmas of scientists. "The Scientific American" of July 16, 1887, tells us that Captain E. D. Dalton has calculated that the depth of the Charleston earthquake was 12 miles ; statute miles, it is to be supposed, as nothing is said to the contrary. To reach the temperature of 412 this would give an increase of i in 45 metres in depth, which is a considerably greater depth than what we have estimated, but does not invalidate our reason- ing, as it has always been known that the gradient of increase New Theories in Astronomy. 209 of heat varies considerably from one place to another. Be- sides, and more especially, Charleston being a seaport, and, consequently, not far from the level of the sea, it is to be supposed that, owing to the presence of water, the cooling of the earth has penetrated to a greater depth there than in the heart of Italy. The same authority states that in the formid- able Yokohama earthquake of 1880, the mean depth was only 3 J miles. The mention of mean depth here makes us notice that the 12 miles may have been the extreme depth to which the earthquake, or shock, was felt at Charleston, and that the focal depth may have been considerably higher up than that Be that as it may, there is no proof existing that water or even steam can penetrate into the earth more than a very few miles, much less to hundreds of miles. Having referred pretty freely to the aqueo-igneous mag- mas, supposed by some scientists to exist deep down in the interior of the earth, it is but fair to give our reasons for refusing to believe that there can be any such mixture in any part of it, or anywhere else. In order to do so, we shall first cite some of the bases upon which such ideas have been founded. In " Nature" of December 12, 1889, we find what follows : " Let us now consider the alternative theory suggested by Mr. Fisher. He claims that geologists furnish him with a certain amount of positive evidence for the idea that water is an essential constituent of the liquid magma from which the igneous rocks have been derived. Passing over the proofs of the existence of water in the crystals of volcanic rocks, and in the materials of deep-seated dykes, let us come at once to the granite, a rock which can only have been formed at great depths and under great pressures, and which often forms large tracts that are supposed to have been subterranean lakes or cisterns of liquid matter in direct communication with still deeper reservoirs. . Now, all granites contain crystals of quartz, and these crystals include numerous minute cavities which contain water and other liquids ; and the quartz of some granites is so full of water-vesicles that Mr. Clifton Ward has said : ' A thousand millions might easily be contained within P 2io New Theories in Astronomy. a cubic inch of quartz, and sometimes the contained water must make up at least 5 per cent, of the whole volume of the containing quartz/ This amount only represents the water that has been as it were, accidentally shut up in the granite, for some was doubtlessly given off in the form of steam which made its way through the surrounding rocks." , We cannot follow Mr. Fisher in " passing over the proofs of the existence of water in the crystals of volcanic rocks and in the materials of deep-seated dykes " ; because the presence of water in these crystals when examined in a laboratory is no proof that water was present in them when they were liquid, and before they put on the form of crystals. There is no analogy between them and General Wade's read. Any crystals that a man can pick up anywhere, even from the mouth of a volcano, are quite capable of absorbing vapour of water from the atmosphere before he can carry them to his laboratory. All matter is supposed to be pervaded, more or less, by the ether, and there is always an open road for it> i.e. the vapour of water to enter by. Nature dives more rapidly into a piece of rock than a man can walk or drive down from the summit of a volcano, so that getting water out of it when he is in his laboratory, is no proof that the water was there when the piece of rock was at the bottom, not the mouth, of the volcano. The minute so-called water-vesicles in granite have only served the purpose of a snare to facilitate his deceiving himself, by the help of Mr. Clifton Ward, to further his speculations. For we think it would have been far more natural for him to have supposed that these vesicles were originally filled with the all-pervading ether. Or, are we to prohibit the ether from being present anywhere, except where it suits us ? Even the dimensions given to the vesicles of a thousand millions of them being contained in a cubic inch makes us at once think of something more ethereal than water. And the whole object of Mr. Fisher's argument is to show how the depth of the ocean may be increased by water expelled from such magmas, A hollow planet, with compressed gases in the centre, raises the idea of the possibility of explosion. It would have New Theories in Astronomy. 211 furnished Olbers, or any follower of his, with the bursting force to shatter into fragments the planet, out of which he supposed the asteroids to have been made. It need not cause any alarm with respect to the earth, whose shell is very much thicker than that of the exploded planet, seeing that its whole mass has been estimated not to have exceeded one-fourth of that of the earth (see Table I.). The 5000 atmospheres of pressure we have spoken of could have no such effect on so thick a shell as the earth's ; and we cannot increase the number without diminishing its average density, as we have shown. When we see Mars blown up, whose diameter, and consequent thickness of shell, are not much more than half those of the earth, we may begin to think of getting out of the way. THE MOON. This satellite is supposed, according to the nebular hy- pothesis, to have been at one time neither more nor less than a smaller edition of the earth itself, endowed with atmosphere, plains, mountains, volcanoes, rivers, seas, rotary motion, etc. ; previous to which it had passed through the same stages of gasiform, molten-liquid, and solid as its parent had done. One would think that its almost perfectly round form proves to demonstration that it must have rotated rapidly on its, or an, axis at one time ; but there are some astronomers who think that it has never rotated at all, an opinion in which we cannot concur by any means. When it arrived at the stage of having seas, the tides raised in them by the attraction of the earth must have acted like a brake on its rotation in the same manner as its attraction is supposed to be now doing on the earth and gradually reduced it until it ceased altogether ; from which time forward it must have always presented the same side to the earth. It has been thought that the tides raised in it by the earth would be so tremendous that they would prevent anything like rotation having ever existed ; but everything requires to be accounted for, and the only way to account for its perfectly circular form is by its having rotated. P 2 212 New Theories in Astronomy. Considering, then, the moon as having been dispossessed, absolutely, of rotation and reduced to the single motion of revolution round the earth as far as we are at present concerned, at least we can go back to the period when this change came over it, and consider what would happen about the time, and immediately after the rotation came to an end. When a fly-wheel is made to revolve rapidly and is then allowed to run until it stops, it very seldom comes to rest all at once, and generally swings backwards and forwards something like a pendulum, until it finally stops ; because it is always a little heavier on one side than the opposite, even should the difference of weight be only that of the handle by which it was set in motion ; so we may suppose it would be with the moon when at last it failed to turn the centre, as it is called the tides, the retarding cause, giving origin to the difference of weight on opposite sides and we can conceive what com- motions would be created on its surface by the wobbles it would make. We can imagine how the seas would rush backwards and forwards over the lower land and hills, levelling them down to the flat plains that are seen spread abroad among the innumerable volcanoes which cover the side turned towards the earth, until it finally came to rest. When the commotions ceased and the centrifugal force of the moon's revolutionary motion round the earth which is over 38 miles per minute came to act freely, we know that the atmosphere and seas, being the mobile parts of it, would be pretty nearly all driven off very quickly to the side farthest from the earth, perhaps even before it came to the final state of comparative rest, whose translation would involve mighty rushings of waters there as well. Also, that all the liquid matter in its- interior, being so much heavier and more difficult to be moved by centrifugal force, would gravitate towards the side nearest the earth, whose attractive force would soon put an end to anything in the form of interior tides of molten matter, which very probably existed up till that period. If the moon came to a stop without any wobbling, then the transference of atmosphere and seas to the farthest off hemisphere, and the gravitation of the liquid matter of the interior to the side New Theories in Astronomy. 213 nearest to us, might be more gradual but would finally and certainly come to pass. And here we must specially note that if it made one rotation for each revolution, or one rotation in any length of time or under any circumstances whatever, these transferences of matter from one hemisphere to the other could not have taken place, because there would be no stationary region to which they could be transferred by centrifugal force, as each part of its circumference would in its turn occupy that region. And above all be it specially marked because the moon would not, in that case, always present its same side to the earth. Looking upon the moon as a hollow sphere of somewhat the same proportions as we have made out for the earth, the region of greatest density would be at about 234 miles deep from the outer surface, the interior surface of the shell at the depth of 692 miles, and the hollow centre 776 miles in diameter, as long as it continued to rotate upon its axis. When that motion ceased and the seas were transferred to the hemisphere farthest off from the earth, and the liquid matter in the interior had gravitated towards the nearest, as we have just said above, its conditions would be very materially altered. Lest it should be supposed that with a very thin crust, nearly its whole mass would gravitate to the side nearest to the earth, let us always bear in mind that the moon would be virtually solid to not far from the inner surface of the shell, through the pressure of superincumbent matter, both from without and from within, in the same manner as we have considered the earth to be. Whatever water had been ab- sorbed by the crust when it was still rotating on its axis which, at most, could have penetrated only a few miles and even whatever lakes or inland seas might have been left on the surface always seen by us, would be soon evaporated by the internal heat, and the heat radiated by the sun which Sir John Herschel has calculated to be greater than boiling water and driven off in the shape of vapour in the same manner as the atmosphere had been. These transferences would lead to two consequences, each one of its own nature, which we must not fail to notice particularly, as in great measure they 214 New Theories in Astronomy. explain to us the constitution, or rather the construction, of the moon, (i) All air and vaporous matter being translated to the unseen hemisphere would tend to cool it more rapidly and deeply than the other, not only on account of the cooling powers of the water, but from the atmosphere and vapours preventing the heat of the sun from acting so powerfully upon it. (2) On the other hand, owing to the accumulation of melted, or liquid, matter in the interior of the side now turned permanently towards the earth, the formerly solid part of that side would tend to increase in temperature, which, joined to the heat from the sun not intercepted by any atmosphere, and continuing without interruption for a fortnight at a time, would produce a great difference in the temperatures of the two hemispheres. Thus it is natural to suppose that the thicker and cooler solid shell on the one side would tend to weaken and drive down the volcanic forces to a greater depth ; while the greater temperature and thinner solid shell on the other, the down side the one next to the earth would have an exactly opposite tendency and would bring them nearer to the surface. In this manner we seem to find a very plausible reason for the great exuberance of the volcanic forces displayed on the surface of the moon always presented to us. Both the interior construction and exterior form of the moon, as modified by losing its rotary motion, would no doubt be very different to that of a hollow sphere rotating on its axis ; but Hansen's " curious theory " has prepared us for this, by showing that some anomaly in its construction had been noted and commented upon, although the existence of the anomaly was not attributed to the atmosphere on its having been driven away to the far-off hemisphere. But with this subject we have dealt pretty fully already in Chapter II., which may be referred to for further explanation if required. New Theories in Astronomy. PAGE 215 216 217 218 219 221 222 22 3 223 22 4 CHAPTER XII. Some of the results arising from the sun's being a hollow sphere. Repetition of the effects of condensation on the temperature of the nebula. Ideas called up by the apparently anomalous increase of tempera- ture. How heat is carried from the sun to the earth. The sun supposed to radiate heat only to bodies that can receive and hold it, and not to all space. The heat of the sun accumu- lated in a hot box to considerably beyond the boiling point of water. The heat accumulated in this way supposed to be due to a peculiar function of the ether, as it is a fact that heat can be radiated from a cold to a hot body. The sun must be gaseous, or rather gasiform, throughout. No matter in it solid or even liquid. Divisions and densities of shell. The hollow centre filled with gases, whose mass naturally diminishes the mean density of the whole body. The amount of this reduction so far defined. The presence of gases or vapours in the hollow a natural result of condensation. The hollow centre filled with gases not incompatible with the sun's being a hollow sphere. The temperature at the centre may be anything, not depending on any law of gases. Further exposition of hollow-sphere theory put oft till after further development of the construction of the sun. IN the last chapter we have endeavoured to point out how much our knowledge of the interior construction of the earth and moon has been increased, and how many difficulties in the comprehension of their construction are overcome by the .fact demonstrated in previous parts of our work that they are hollow bodies ; and we now proceed to show some part of what may be learned from studying the sun under the same conception of its being a hollow body. We say part of what may be learned, because the whole seems to us to be so great that it would take much more time and space, not to speak of knowledge, than we can devote to the subject to make even a 2 1 6 New Theories in Astronomy* proper beginning to such a study. To our sight it takes away the necessity for guessing in the dark at what the construction may be, which is all that has hitherto been done ; and furnishes the means of discovering, with intelligent study and investigation, what most probably is the actual consti- tution of the sun. In Chapters V. and VII. we have followed up the contrac- tion and condensation of the residue of the original nebula, after it had thrown off all the known planets ; first, to the diameter of 58,000,000 miles, with density of 3-7 4 tn f an atmosphere and temperature of 273, or one degree of absolute temperature ; second, to about 9,000,000 miles diameter, with density equal to air at atmospheric pressure, and temperature represented by zero of the centigrade scale, or what has been hitherto called 2/4 of absolute temperature ; third, to 4,150,000 miles diameter, with density equal to ten atmos- pheres and temperature of 2740 of actual, or 2742 of absolute temperature ; and fourth, to 972,895 miles diameter, with density equal to water and temperature which we do not venture to express. All these stated densities and tempera- tures are understood to be average, the temperatures being those the various stages would have had, had no heat been radiated into space by them. Here, then, we might go on to set forth what might be the interior dimensions, various densities, and conditions of each one of the four stages, under the conception of their being all hollow spheres, and afterwards carry on a resume of the whole of them and apply it to the sun as it is at the present day ; but this, in addition to involving an immense deal of difficult work, subject to errors and omissions in operation, would not do much towards enabling us to explain in a more simple way what may be, most probably is, its interior construction. We shall, therefore, look upon the four stages as represented by a model having the diameter and other knewn measure- ments of the sun in its present state. To begin what we propose to do we believe it is necessary to repeat, as a thing that has to be borne in mind, that when we had contracted the original nebula from 6,000,000,000 New Theories in Astronomy. 217 miles in diameter to 58,000,000 miles, its density was only equal to a barometric pressure of one-ninth of an inch of mercury, and its mean temperature had been increased only one degree, that is, from 274 to -273; and we can add that, although we had given the original nebula ten times that diameter, the result both in density and temperature would have been the same when it was condensed to 58,000,000 miles in diameter. Then, again, we believe it necessary to repeat that by contracting the nebula from 58,000,000 to 9,000,000 miles in diameter its mean density was raised from 2Vi tn f to full atmospheric pressure, and its mean temperature from 273 to zero of the ordinary centigrade scale, i.e. to the temperature of freezing water. These two results strike us, at first sight, as somewhat remarkable, seeing that what looks like almost unlimited condensation to 58,000,000 miles dia- meter produced only one degree of temperature, while the comparatively insignificant condensation of from 58,000,000 to 9,000,000 miles in diameter produced 273 of heat, in the 2uay we are accustomed to measure heat. Following up these two facts gives rise to ideas that have been borne in upon us ever since we stumbled upon them when making the analysis of the nebular hypothesis. One of these notions was that, were it practicable, the most effec- tual mode of liquefying gases would be by putting any one of them into a sealed vessel, and confining it in another vessel in which a vacuum of g^th part of an atmosphere could be produced ; no difficult matter as far as the vacuum is con- cerned, for a good exhausting air-pump would be all that is required. But the practicability? The vessel in which the vacuum is produced would have to be protected so that no extraneous heat could be conveyed or conducted into it in any way whatever. How this could be, or is, done without cutting off every possibility of manipulating the enclosed vessel, we do not see ; but it seems evident that some method is available because something presenting the same difficulties has been actually done, as everybody knows. The only degree of vacuum of any use in the exterior vessel would be about one-ninth of an inch of mercury, because that would C 2i8 New Theories in Astronomy* as we have just said, furnish a temperature of 273. There would be no necessity for applying pressure to the gas ex- perimented upon. In fact pressure would be an obstacle to the experiment, according to the theory of the air thermo- meter ; and could only be of use by furnishing a larger quantity of liquid to be handled and examined. Another idea is that there can be no such condition as absolute zero of temperature of what we are accustomed to think of as a gas, as far as science is concerned ; as on arriving at that condition, perhaps long before, any gas would slip out of its hands altogether. But there is a much more rational reason than this, which we have brought forward on a former occasion. We are taught that heat is a mode of motion, which means that as long as there is heat there will be motion to account for it, so that motion would have to be annihilated on the earth before absolute zero of temperature could be reached. We have, then, to come back to what we said when treating of the heat of space, and look upon the temperature of the vibration of the ether as being the lowest that can be measured by science. We said then that it must be far below 225. Since then a temperature has been reached of within 23 or 24 of absolute zero, according as that condition is measured by 273 or 274. This, of course, leads us to think of the ether as a carrier of light, heat, etc., and of how it can carry heat to the earth without becoming heated itself, as there can be no doubt about its being a material substance. How it can bring what may be called considerable heat to the earth and still have little or no heat in itself ; even should it turn out, which we do not believe possible, that the estimates of the heat of space of 150 and 142, made about the beginning of this century by Sir John Herschel and Pouillet, turn out to be near the truth. We have seen, in " Nature "of July 15, 1886, a monograph by Captain Ericsson, in which he shows that the heat radiated by the sun to where his rays strike our atmo- sphere is somewhere about 83 F., and it is not easy to see how radiated heat can be transmitted through 90 million miles of space at a temperature of much lower than 225, New Theories in Astronomy. 219 and reach the confines of our atmosphere with the heat of 83 F. There is one supposition that occurs to us under which this can happen, and that is, that the sun only radiates heat to bodies which can receive it, and does not radiate it into all space where there is nothing but the ether to hold it. This, of course, implies that the ether acts the same part the part for which it was really invented with respect to heat that a telegraph wire does with respect to electricity ; in which case, .we could imagine that it starts from the sun with the maxi- mum heat radiated by him, and that this goes on decreasing in the ratio of the square of the distance it travels through, the same as is understood to be the case with all radiated heat ; and that the part of space not occupied, for the time necessary, by these connexions might be supposed to form the return current which we believe must exist, just the same as the earth does for electricity. For that there is a return current is demonstrated by the fact that the earth radiates heat into space when the sun is not shining upon it. Again, even in this case, we have another difficulty thrown upon us, over and above that cited by Captain Ericsson, of the heat delivered at the bounds of our atmosphere being about 83 F., by our being informed in" Engineering" of December^ 1885, that : " A hot box, contrived to observe the temperature which could be attained by the unconcentrated solar rays> was used on Mount Whitney, 12,000 feet above the sea" well within the limits of our atmosphere " and that the en- closed thermometer rose to 233 * 3 F. on September 9, I p.m., 1 88 1, the shade thermometer then reading 59'8F." How are we to comprehend these two facts ? We have seen a way of getting over part of the first fact as far as to the boundary of our atmosphere, but from there we have to carry 83 F. to the top of Mount Whitney, through the atmosphere there and present it along with the other lot in the hot box at 233 ' 3 F. We may get the beginning of what may be an explana- tion of all the facts from another part of Captain Ericsson's monograph, where he says : " Engineers of great experience in the application of heat for the production of motive power 22O New Theories in Astronomy. and other purposes deny that the temperature of a body can be increased by the application of heat of a lower degree than that of the body whose temperature we desire to augment The soundness of their reasoning is apparently incontro- vertible, yet the temperature of the mercury in the instrument just described raised to 600 F. by means of the parabolic re- flector, increases at once when solar heat is admitted through the circular apertures, although the sun's radiant intensity at the time may not reach one-tenth of the stated temperature. It should be mentioned that the trial of this new pyrhelio- meter has not been concluded, owing to very unfavourable atmospheric conditions since its completion. For our present purpose the great fact established by the illustrated instru- ment is sufficient, namely, that the previous temperature of a body exposed to the sun's radiant heat is immaterial. The augmentation of temperature resulting from exposure to the sun, the pyrheliometer shows, depends upon the intensity of the sun's rays. A little study shows us that the steam engineers are per- fectly right in their doctrine. The heat of steam can only be called a variety of the temperature of water. At 300 Ib. pressure per square inch the heat of steam is 417*5 F., while at 20 Ib. pressure it is only 228-0 F., and therefore the steam engineer has good reason to say that steam at the lower pressure or derived from heat that can only produce that pressure can add no heat to the higher ; on the contrary, the only possible means of applying the heat of the lower to that of the other would be by mixing them, and we know what the result of that would be. This brings before us the fact that the steam engineer's heat is very limited, and can only be communicated in certain ways, while the sun's heat is comparatively unlimited, and can only be communicated to anything through the medium of the ether. But it pro- bably teaches more than that. Were the engineer's heat unlimited in quantity at low pressure it can easily be believed that it could be transmitted to another body at any tempera- ture by radiation, the same as it is radiated from the sun to a hot box ; but it is not, and we thus seem to find that radiation New Theories in Astronomy. 221 is a mode, possessed by the ether alone, of conveying heat from one body to another. It has nothing whatever to do with mixing, conduction, convection, or anything, except in so far as the ether is mixed in a more or less limited quantity with all matter. In support of this idea we can refer to Professor Tait's treatise on heat, where we find it stated that " heat does pass (though on an infinitesimal scale) from colder to hotter bodies " ; and we can easily understand that the infinitesimal quantity so passed is due to the comparatively infinitesimal quantity of ether there is in either of the two bodies to perform the work of transference. Professor Tait has not told us how heat is carried from a cold to a hot body, but there can be no doubt about its being a function of the ether which can only be found out by a careful and analytical study of that agent. Such a study we propose to undertake presently without much expectation of being successful, but still with the hope of helping in some measure to find out how the ether operates. Meanwhile we shall return to what we had begun to say about the sun being a hollow sphere, and to our proposal to treat of the nebula contracted from 58 million miles to its present diameter, as if it were a model representing a r&umJ of all the effects produced on the nebula by that amount of condensation. We know from all our work that the sun must be a gasi- form body, which means that all the cosmic matter contained in it must be in the form of vapour, even although its consis- tence should outrival a London fog notwithstanding that some physicists have supposed that it may be solid at the centre through extreme pressure and it is not altogether correct to compare its construction to that of a solid body such as the earth ; but as we have no other we shall begin to make a comparison with it, which, it will be found, can lead us into no appreciable error. Considering then the sun to be 867,000 miles in diameter, with mean density of I -413 that of water, the hollow part being still completely empty, and applying to it the same proportion we have deduced for the earth, we find that the region of greatest density would be at '7937 f tne radius of the sphere a proportion really 222 New Theories in Astronomy. derived from the line of division into two equal parts of the volume of a sphere from the centre, or 89,43 [ miles from the surface ; and the inner surface of the shell at 0*548 a pro- portion derived from our calculations for the earth of the radius of 433,500 miles, or 237,558 miles from the centre ; which in turn makes the shell to be 195,942 miles thick, and the hollow centre to be 475,116 miles in diameter. On the other hand, still following the proportions derived from the earth, we find that the density at the surface might be one- third of the mean density or 0*471 ; that it might be one-fifth greater than the mean, or I / at the region of greatest density and one-half, or 0*71 at the inner surface of the shell all of these three densities being in terms of water. Now, the hollow centre of 475,116 miles in diameter would have a volume of one-sixth of the whole volume of the sun, which, filled with gases, would diminish all these densities just in proportion to what may be considered the degree of compression and condensation the gases might be subjected to. That there should be gases in the interior hardly requires to be more than stated, as there can be no doubt that the degree of heat to which the shell had arrived by the time it came to have the dimensions above mentioned, would be amply sufficient to excite chemical action among the elements of which the sun is composed ; and the gases or vapours produced by that action would flow as naturally towards the interior of the hollow centre as towards the space beyond the outer surface of the shell, until they were stopped by increase of pressure, which of course would mean increase of density in this case. We see then that if the hollow centre has a volume of one-sixth of the whole volume of the sun and we multiply this volume by 6, we have a mass equal to the whole mass of the sun, were its mean density only the same as that of water. Consequently, if we multiply the said volume by 6 and by 1*413, that is by 8*478, we get a mass equal to the whole mass of the sun at its known mean density. Again, were we to suppose the hollow centre to be filled with gases of the same specific gravity of air, condensed to a pressure of 6560 atmo- spheres which would correspond in density to 8*478 times New Theories in Astronomy. 223 the density of water we should have in the hollow centre alone a mass equal to another sun, in addition to the one made up by the dimensions and densities stated above. We see then that if we fill the hollow centre with gases at the pressure, and with the density just stated, we have a sun of twice the mass it should be. But if we leave the specified gases in the hollow with one-half of the above density, and deduct the equivalent mass of the other half density of the gases from the shell, as estimated for the hollow centre, we should have a sun of the mass required by astronomy. In this way we should have the three specified densities reduced from 0-471, 1-70 and 0-71 to 0*236, 0-85 and 0-355, f r tne outer surface, the region of greatest density, and the inner surface of the shell, respectively ; and the pressure and density of the gases in the hollow centre reduced to 3280 atmospheres. Thus, from what has just been shown, which at first sight may be thought very irrelevant matter, we discover that it is not necessary that there should be any matter in the sun even so dense as water. And still we have to think of what an insignificant pressure three or four thousand atmospheres would be in the centre of the sun. No one will pretend to allege that no gases can be pro- duced in the shell of the sun, or to say anything against those formed in the inner half of it finding their way to the hollow centre, and going on increasing there till they were able to force their way out through the shell ; that is, until their pressure was equal to the resistance offered by the gaseous body of the sun, or against their temperature increasing until it came to correspond to their density and most probably rising to a much higher degree. Such, then, must even now be the construction of the sun, as reduced to its present diameter and density. That is, a hollow sphere consisting of cosmic matter combined with gases and having a hollow centre filled with chemically formed gases or vapours. Here it may be argued that the sun ceases to be a hollow sphere, but that is not so. The most that can be said about it is that it is a hollow sphere with the empty part filled up. It would only be in much the same condition as a hollow 224 New Theories in Astronomy. globe of iron filled with melted antimony or bismuth. Its construction would be in no way changed by the empty hollow being filled up, so long as its condition remained gaseous not changed to liquid or solid. The only difference in our sphere would be that its density would virtually be the same from what we have called the region of greatest density to the centre, which would not only involve a greater distance of that region from the surface of the sphere, but another reduction of the above mentioned densities of the sun ; for we cannot in any way imagine that the pressure in its interior can be less than many thousands of atmospheres. Whatever may be the relative densities of the shell and the gases in the hollow, they will have no necessary effect upon the temperature of the latter, because, let the densities be what they may, the gases might be cooled down to absolute zero of temperature, or raised to any imaginary degree with- out any change being made in their weight as long as their volume was maintained the same. This has been proved by laboratory experiments almost as far as possible. Gases at very high degrees of pressure and consequent densities have been cooled down to not far from the absolute zero of tempera- ture, while others under very low pressures have been heated up to nearly as great heat as the enclosing vessel would bear, without their weight being altered in either case ; but in the sun there is a larger laboratory in which we can place no limit to pressure or temperature. We know, however, that pres- sures are required sufficiently great to blow out jet promin- ences with velocities of 100,000 miles per second or more, to heights 200,000 and even 350,000 miles above the photosphere ; and if we knew what these pressures are we might be able to learn something about the minimum temperatures of the gases. To obtain these pressures we have- in the construction we are advocating a real containing receptacle with sides 195,942 miles thick, in the outer half of which we have the compressing force, due to the gravitation of the whole mass of the sun acting at the centre, and over and above, both in it and the inner half, we have the cohesive force of the matter of which it is composed. In fact we have a sun whose con- New Theories in Astronomy. 225 struction we can understand, in which we have gases shut up without their expansive forces being impaired in any way, ready to be exerted with full energy whenever they are relieved from compression by any commotions in any part of the whole body, and taking their part in keeping the whole of the matter composing it in constant motion. How these commotions are produced it is not difficult to explain to a very considerable extent at least, but this we must leave over until we have reconstructed the original nebula, and shown how the solar system could be elaborated from it, almost exactly in the way conceived by Laplace in his nebular hypo- thesis. We shall then also be able to extend our exposition of what is to be learnt from our mode of construction, and to still further reduce our estimate of the mean density of the sun. Meanwhile we have to go into another long digression, with the view of trying to find out something about what the nature of the ether is or may be, which we think to be quite necessary before we go any farther. Q 226 New Theories in Astronomy. CHAPTER XIII. PAGE 226 The ether. Its nature considered. Behaves like a gas. 227 Can be pumped out of a receiver. 228 Light and heat do not pass through a tube in vacuo. Laboratory experiments examined. 229 Light and darkness in a partial vacuum, though high. 230 Electricity not a carrying agent. 232 Why there are light and dark strata in a high vacuum. 233 The real carrying agent through a high vacuum is the residue of ether left in it. Digression to consider the aurora. 234 How air may be carried to extraordinary heights. Zones of air carried up are made luminous by electricity. 236 Comparison of this method with experiments quoted. 237 Experiment suggested to prove whether light passes freely through a vacuum tube. 238 The ether does not pervade all bodies freely. 239 It must be renounced altogether or acknowledged to be a material body, subject to expansion, condensation, heating or cooling. 239 How light and heat pass through glass. 240 Temperature of the ether variable. Zodiacal light, cause of. THE ETHER A MATERIAL SUBSTANCE, PROVED BY ITS BEHAVIOUR. WE have said in a former part of this work, pages 153 and following, that if the ether is capable of performing all the functions that are attributed to it, it must have some con- sistence or substance of some kind ; that it must be matter of some kind in some form, and consequently must have density in some degree however low ; and we might, for the same reasons, suppose that it must have some temperature ; but as long as we believe that without motion there can be no heat, we cannot conceive it to have any temperature. No doubt we might suppose it to be in a constant state of vibration, and to have the temperature corresponding to that state, whatever that may be ; but this, in addition to leaving us just where we were, would only entail upon us the task of New Theories in Astronomy. 227 supplying temperature as well as density to a body of whose existence no positive proof has hitherto been given, whatever we may believe about it. At the same time, the evident necessity of taking its temperature into consideration, seems to supply another reason for concluding that it is a material substance, over and above those we have cited now and before. The general belief regarding the ether has been, ever since it was invented, that it is a substance of some kind (imponderable and impalpable?) which fills and pervades all space and matter ; but a little consideration will show that this belief requires to be modified. The ether is supposed to be the connecting link of the universe, and the agent for carrying light, heat, electricity, and magnetism from the sun to the earth and planets, and all over space ; but it has been found that electricity will not pass through a vacuum, such as has been produced by experimenters, unless it be with a very powerful current. This, of course, would seem to prove that there must be almost no ether in such a vacuum ; because if there was ether in it, of the same density as there is in space, electricity would pass through it with the same ease as it does from one body to another on the earth or in space ; it would seem, also, to justify us in inferring that electricity would not pass through an absolute vacuum at all, however powerful the current might be, because there would be abso- lutely no ether to carry it ; and, likewise, that the quantity of ether remaining in the experimenter's receiver had as much to do with the passing of a very powerful current of electricity through it perhaps a great deal more as the small quantity of air, or gas, or dust not altogether exhausted from it, to which the experimenters attribute its passage. Moreover, it would appear that when air or any gas is pumped out of a receiver, the ether mixed with it is pumped out along with it ; consequently it must be a material, tangible substance, possessing density in some degree, however low it may be. Here, then, we have, it would appear, proof positive that there is such a carrying substance as the ether has been supposed to be. It is a thing which we have not to conceive of, fabri- cate, or build up in our minds. It is a thing we can pump Q 2 228 New Theories in Astronomy. out of a tube, and is as much a material substance, in that respect, as air or any other gas that is as invisible as itself yet nevertheless in the tube until it is pumped out. Against this idea of the nature of the ether, and what may be done with it, it may be argued that light and heat pass freely through a tube or receiver in vac2to, when electricity refuses to pass ; but are we sure that they do pass ? It would be a much more difficult matter to prove that they do, than to prove that electricity does not, because our eyesight gives us evidence in the latter case. Besides, there are facts which, when thoroughly looked into, induce us to believe that light actually does disappear gradually from a vacuum as it is being formed. In an article on " The Northern Lights," in " Science for All," Vol. II., reference is made to a well-known laboratory experiment in the following words : " We take a glass cylin- der, covered at the ends with brass caps, one of which is fitted with a stop-cock, which we can screw to the plate of an air- pump. To the brass caps we now attach the terminals of a powerful induction coil, but as yet we perceive no result. We now begin to exhaust the air from the cylinder, and as the exhaustion goes on we soon see a soft tremulous light begin- ning to play about the ends of the cylinder ; and this, when the air is sufficiently rarefied, gradually extends right through the cylinder. As we continue the exhaustion these phe- nomena will be reversed, the light gradually dying away as the exhaustion increases. We shall at once perceive how very much this resembles an aurora on a small scale, and so we have electricity suggested to us as the agent which pro- duces the aurora." Farther on in the same article we find that : " Aurora displays usually take place at a great height sometimes so high as 300 miles while their average height is over 100 miles. At such heights the air must be extremely rarefied, and we should be disposed to expect that the electric discharge could not take place through it." Now, at the beginning of this experiment, it must be granted that light was passing freely through the glass cylin- der from side to side, and also that, when the electric current New Theories in Astronomy. 229 was turned on, the electricity was passing freely through the air in the cylinder though it was not visible. It could not pass through the glass on account of its being a non-con- ductor. Then, when the air had been partially exhausted from the cylinder, and the " soft tremulous light " began to appear about its ends, it is clear that some interference with, or change in, the free passage of light through it must have been produced, both transversely and longitudinally, which occasioned the difference in the appearance of the light and caused its tremulous motion. And as change in the appear- ance of the light extended through the length of the cylinder as the exhaustion increased, and finally died away light, change and all when it approached more nearly that of an absolute vacuum, we cannot help concluding that the light disappeared because there was no medium left in the cylinder, of sufficient density at least, through which it could pass ; which, of course, means that light cannot pass through a vacuum any more than electricity can. The experiment we have cited above may be considered antiquated, but similar results are presented to us in Professor Balfour Stewart's " Elementary Physics," where he says at page 399 of the Reprint of 1891 : "Another peculiarity of the current is the stratification of the light which is given out when it traverses a gas or vapour of very small pressure. We have a series of zones alternately light and dark, which occa- sionally present a display of colours. These stratifications have been much studied by Gassiot and others, and are found to depend upon the nature of the substance in the tube." [The ether ?] " If, however, the vacuum be a perfect one, Gassiot has found that the most powerful current is unable to pass through any considerable length of such a tube." [In passing, we take the opportunity to assert, with con- fidence, that there can be no perfect vacuum on the earth.] Here we see the gas or vapour in the tube divided into zones alternately light and dark, which occasionally present a display of colours, and are led to infer, from the colours depending upon the nature of the substance in the tube, that they disappear altogether when the exhaustion is sufficiently 230 New Theories in Astronomy. great ; and are finally told that the most powerful current is unable to pass through such a tube of any considerable length. In this case also, we can say with perfect confidence that there can be no ether left in the tube, in sufficient quantity, or else it would be able to carry the electricity through it much more easily than from the sun to the earth, or from one part of the earth to another. If we refuse to acknowledge that the ether has been removed from the tube or cylinder, we are forced to conclude that it is not the carrying agent, for which alone it has been called into existence by the imagination of scientists ; and we have to invent new theories, new methods for explaining what we have been accustomed to think we thoroughly understood. We have to look for a new dog to carry and fetch. Furthermore, all that has been said about electricity is equally applicable to light, whether we can prove it or not. If light could pass freely through the experimental cylinder from side to side, as it was certainly doing before the exhaustion was begun, we cannot understand why there should be, first tremulous light which finally disappeared, and why dark strata were displayed in it by the forced passage of electricity ; unless it was that the carrier of the light was re- moved, and then we naturally think' of why there should be dark strata in the tube. We can understand electricity light- ing up darkness, but not its darkening light it lightens up midday and we must conclude that both the one and the other were driven through the cylinder, or similarly conducted through it, by the same force, or were left behind. Following up the quotations we have already made from " Science for All," Vol. II., we now add another for further illustration of what we have been saying, to wit : " Let us now return to the laboratory, and see whether we can make any experiment which will throw light upon this difficulty. If we send the electric discharge through one of the so-called vacuum tubes choosing one which consists, through part of its length, of tube which is much narrower than the main portion we find that when the discharge is passing the pres- sure is greater in the narrow part of the tube, showing that in some way gas is being carried along by means of the current, Ne-w Theories in Astronomy. 231 and Professor A. S. Herschel suggests that in some similar way air may be electrically carried up to these great heights." This quotation, of course, refers to the Northern Lights, but it serves to illustrate what we are seeking to show with respect to the ether. In this experiment, the explanation of the pressure being greater in the narrow part of the tube, is exactly the same as that for water passing through a conduit which is narrower at one place than another. The same quantity of water has to pass through the narrow as through the wide part, conse- quently the velocity and pressure (head) have to be greater than in the wide part the water arranges that for itself; and the seeming difficulty of explanation arose from the idea '* that in some way gas is (was) being carried along by the current," when it was only the gas that was being lighted up more vividly by the electricity passing through it, because the same amount of electricity had to be carried through the narrow part as the wide one. No portion of the gas could be carried along with the electricity, else it would very soon have been all accumulated at one end of the tube, or a reverse current must have been set up to restore the balance, which would speedily have shown itself. Had the said tube been filled with copper instead of gas, the experimenter must have known that the electricity, in passing through it, would have spread itself all through the wide part, and contracted itself to pass through the narrow part, spreading itself out again through the other wide part, thus giving rise to differences of pressures and velocities at the different widths of the tube ; but, of course, he would not have been able to see this, because the electricity could hardly be in sufficient quantity to light up the copper, or to impart to it sufficient heat to make it visible. Neither would the electricity carry with it part, or the whole, of the copper when passing through the narrow part. It would be the gas lighted up more vividly, not set in motion, by the electricity that the operator saw in the experi- ment under discussion, and, no doubt, if the tube had been sufficiently exhausted of gas, the light would have disappeared the same as in the first quoted experiment, and the electricity 232 New Theories in Astronomy. would have ceased to pass because there was nothing, in sufficient quantity at least, to carry it along, not even the universally commissioned monopolist the ether. Let us ask here : Does not all this seem to prove that electricity is a carried, not a carrying, agent ? In the quotation made, at page 229, from " Elementary Physics," we are told that when electricity passes through a gas or vapour of very small pressure, " We have a series of zones alternately light and dark." Now we ask, Why should part of these zones be dark ? and the only answer to be given is simply because there is no light in them, nothing in them to carry or hold light. Otherwise, we cannot under- stand why they should appear to be dark. We cannot imagine a glass tube with light and dark zones in it longitu- dinally we have understood the zone to be longitudinal ; transverse sections would not be zones at the same time that light is passing freely through it transversely, i.e. from side to side, unless it is that in the dark zones there is nothing, not even the all-pervading ether, to carry or hold light in ; there- fore, we conclude again that there is no light where there is no ether. For an explanation of the existence of light and dark zones in the almost exhausted cylinder or tube, we refer to Pro- fessor Tait's treatise on " Heat," where he says, in section 358, " What happens at exceedingly small pressures is not certainly known. In fact, if the kinetic gas theory be true, a gas whose volume is immensely increased, cannot in any strict sense be said to have one definite pressure throughout. At any instant there would be here and there isolated impacts on widely different portions of the walls of the containing vessel, instead of that close and continuous bombardment which (to our coarse senses) appears as uniform and constant pressure." Admitting the truth of the kinetic theory of gases, we can see that in a vacuum so rare that only electricity at a very high pressure could be forced (carried ?) through it, we have the prescribed conditions in which there cannot be " one definite pressure throughout " the whole tube ; in other words, we shall have some places in a vacuum tube where there is no New Theories in Astronomy. 233 gas at all, or perhaps even ether, and others where the gas is so rare that it takes a powerful stream of electricity to light it up in passing through, whether the lighted-up zones be composed of gas, or of ether, or part of both. If it did not pass, there would be no light-streak even. And further, we have to notice that the light and dark streaks would be changing places constantly, owing to the collisions of the small number of atoms or molecules of the gas, still not exhausted from the tube, driving each other from place to place. All this makes us think of what is the real carrier of electricity through a partial vacuum, through a gas, or through a substance of any kind whatever, and we can only imagine it to be the ether. In that case the conductivity of any substance would depend upon the quantity of ether contained in it, and we can give no other reason for there being con- ductors and non-conductors of electricity. All matter has been thought to be pervaded by the ether, but we have said before that this must be the case in a limited sense only. It can be shown that glass is permeable to ether, and is therefore not an absolute non-conductor. Metals are supposed to consist of atoms bombarding and revolving around each other under the control of ether. Intermediate conductors may have the quantity in them of ether corresponding to their conductivity ; and the compressibility of water, or any liquid, may depend upon the quantity of the ether mixed with its ultimate atoms. Although we consider it to be going rather beyond the course we had laid out for ourselves, we cannot help returning to the article on the " Northern Lights " in " Science for All," quoted above in connection with electricity in the presence of a vacuum ; because it helps to illustrate the subject we are dealing with. In the regions where these Lights are seen, we know that there can be no want of ether, because it is supposed to per- vade all space ; but we know that there must be a very great want of air, or vapour of any kind, due to the height above the earth at which they are seen. Here, then, we have a great 234 New Theories in Astronomy. field for differences of pressures being caused all through it, by the collisions among themselves of the molecules or atoms of the extremely attenuated air ; we have the higher or lower pressed zones of the laboratory experiment spread out before us, and if we suppose currents of electricity to be passed through them, we have an aurora in the high heavens, a counterpart of what was seen in the vacuum tube. The bombardment of the molecules continually shifting their posi- tions and creating zones of different pressures, when lighted up by electricity, would easily account for the flashes, cor- uscations, and changes of the aurora ; but, how does the air get up so high as is stated in the quotation at page 228 ? We cannot accept the supposition of Professor A. S. Herschel that the air is carried up to the height of from 100 to 300 miles by electricity. We must believe, till evidence is given to the contrary, that electricity is a carried, not a carrying, power. Conductors of sound are all material sub- stances ; sound is not. It seems logical, therefore, to conclude that the ether is a material substance, because it conducts light, heat, etc. etc., which are not material substances. Proof is therefore required that electricity is a material substance, before it can be called a carrier. That air does somehow get up so high there can be little doubt, as is satisfactorily proved by the burning of meteorites when they come into our atmo- sphere at heights said to be more than 300 miles. How it does mount up so high is not so wonderful as it seems, when we take into consideration the causes of the trade winds, which are : The upward currents of the air created by the heat of the sun ; the centrifugal force inherent in it at the time of leaving the earth ; and its angular motion, which may be, at a guess, from 10 to 1 6 miles per minute, seeing that the equator has an angular velocity of over 1000 miles per hour. Then, from the time it leaves the earth, the air must begin to lose its angular velocity, the impelling power being cut off, and form a bank higher up, opposing the motion forward of all the air following it, so that immediately above the tropics there must be forward motion and obstruction, producing whirlwinds of which we can see or know really nothing, though New Theories in Astronomy. 235 they must exist, and which may carry air or vapours up to very great heights, carrying with them densities far beyond what would correspond to the simple attraction of the earth. At these heights this attraction would be very much dimin- ished, and almost the only way in which the density of the whirlwinds could be diminished would be by expansion, which would not be very active in bodies already very considerably attenuated, as the whirlwinds would naturally be. Their movement towards the poles would be the same as that of the trade winds has always been supposed to be ; and we can now see how there can be air at great heights in the aurora regions, not carried up by electricity. In fact, the air may, or rather must, have carried the electricity up with it, as we shall, we believe, presently see. We have not supposed that all the air, raised from the earth by the heat of the sun, is carried up to such altitudes and to its polar regions, but only a very small part of it ; and we have to add that there is perhaps not always electricity present in sufficient quantity to illuminate the air when it is carried up, which would, from the nature of its ascent, be undoubtedly divided into zones, streams, or belts at different degrees of tenuity. We do not doubt, or rather we believe, that electricity is always present in the atmosphere ; but we are not sure that it is always so in sufficient force to make itself manifest. A very homely example of this is : Stroke a cat's back in ordinary circumstances, and it will only arch it up in recognition of the caress ; but stroke it on a frosty night and it will emit sparks of electricity. The cat's hair does not shine perhaps fortunately for the cat because the electricity in it is not present in sufficient force, and only shows itself when the hand acting like a brush collects it into sparks. This shows not only that electricity is more abundant in the air at one time than at another, but that it is more so in cold and dry than in warm and moist air. It also shows one of the reasons why auroras of great brilliancy and extent are not continually in play in their own special regions, which is the want of a sufficient supply of electricity ; another reason being, the absence of the requisite zones, or masses of air in 236 New Theories in Astronomy. cyclonic motion at different pressure and in sufficient quantity. We understand from what we have read that the glow of the aurora is seldom awanting in clear weather in the far north, and can imagine that there is always a sufficient supply of electricity and attenuated air to maintain the glow constantly ; and also that the brilliant displays are only made when there is a sufficient influx of whirlwinds of air at low and varying pressures, and of electricity in sufficient force to light them up. We should suppose that the bright flashes would take place where the pressure was greatest, and the illuminated darkness, so to speak, where it was least. Electricity does not carry up air to these heights, neither does magnetism bring it down from the sun ; still a magnetic storm produces brilliant auroras. Confronting these reflections with the laboratory experi- ment we have cited at page 228, we see that they are very fully confirmed by it ; perhaps it would be more true to say that they were originated by it. When the current of electricity was first turned into the glass cylinder, no result was perceived. This must undoubtedly be construed into showing that the light in the cylinder, passing through it from side to side, was more powerful than the diffused light of the electricity passing through it from end to end ; which was the reason why there was no result. By diffused, we mean that the electricity, turned into the cylinder through a thin wire, would immedi- ately spread out over the whole of its width (or cross section) and thus very much weaken its light-giving power. When exhaustion had proceeded to a sufficient extent to produce the soft tremulous light, we can only conceive that the trans- verse light had decreased so far that the diffused light of the electricity, passing longitudinally, had begun to balance it, which caused the tremulous appearance on account of the one beginning to disappear and the other to take its place. And when the light extended through the whole length of the cylinder and the phenomena were reversed ; and when the light died away altogether, when the vacuum became suf- ficiently pronounced ; we can only believe that there was no light at all in it ; neither natural light passing through it New Theories in Astronomy. 237 transversely, nor light of electricity passing longitudinally. Should any one object to this demonstration, as we may call it, we refer him to the quotation, made at page 229, from Pro- fessor Balfour Stewart's " Elementary Physics," and ask him, How could there be dark zones in a tube, through which light ought to pass freely from side to side? The thing appears to be tremendously absurd. There were dark streaks in the tube and other streaks of gas, or vapour of some kind at very low pressures (see also quotation from Professor Tait at page 232) that were lighted up to some extent by the current of electricity, but even these died away. We do not pretend to impugn the idea that the stratification of light and dark zones depended upon the nature of the substances in the tube, we only want to insist that the substances left in it were so extremely rare that electricity could not pass freely through it longitudinally, nor daylight transversely, else there could have been no dark zones in it ; and that even the ether was in such small force that it could not perform the carrying duties assigned to it. We have often wondered whether any experiments have ever been made to ascertain whether any changes, as far as the presence of light is concerned alone, have been brought about by producing a vacuum in a tube. The gradual dying away of light, and its final disappearance, are certainly sug- gestive of changes, and may have excited curiosity to know what actually happens. That there are changes cannot be denied, and it would be satisfactory to know what they are. It appears to us that one simple and easily made experiment would give a good deal of information on the subject. Let a glass tube of cylindrical form one of those prepared for vacuum experiments be placed in a slit in the window- shutter of a dark room, so that absolutely no light can pass into the room except through the hollow part of the tube ; which might be effectually managed by burying two opposite sixth parts of its circumference in the wood of the shutter, and there would still be left one-third of its diameter for the free passage of light from side to side. When so arranged, and when still full of air, let a spectrum be taken of sunlight passing 238 New Theories in Astronomy. through it, to serve for comparison. Then let a high vacuum be produced in the tube, and another spectrum taken and compared with the first. This will at once show whether any change has been produced or not. Should the difference we expect be found, the experiment might be extended by spectra being taken at different degrees of exhaustion, from which some useful information might be derived. We have said, at page 129, that the ether does not pervade all bodies of all classes, and such must be the case in some measure at least, otherwise there would be no non-conductors of electricity, no insulators for our electric telegraphs and deep sea cables. Were glass, for instance, pervaded freely by the ether, and the ether is in reality the carrier of electricity, then electricity could pass freely through glass, but it does not ; therefore, there can be no, or at all events very little, ether in glass or any other insulator. We can see, then, the possibility of the ether being removed from a glass tube, pro- vided it is a material substance, by shutting up one end of it with a stopper of glass and passing a perfectly-fitting glass piston through it to the other end. Suppose this done, it would be quite safe to say that electricity could not pass through the tube, because there would be nothing absolutely nothing to carry it, not even the piston-rod, for we could have that not only made of glass but on the outside of the piston. In this case the result would be exactly the same as when the contents of the tube were pumped out of it, and the residue left, if any, would be the same, that is, an immeasurably small quantity of the ether which had filtered through the glass. It may be argued that it would be impossible to make such an experiment as we have proposed, but that does not damage in the slightest degree the correctness of the conse- quences deduced from it ; any more than the impossibility of constructing a perfect heat engine destroys the deductions drawn by Sadi Carnot, from the study of such an ideal machine. We can grant that glass being not an absolute non-conductor, the ether might, in course of time, ooze through it and fill the tube again, while gas, air, or dust could not so ooze through it, and thus re-establish the current of New Theories in Astronomy. 239 electricity that was stopped for want of it ; but we cannot grant that there was any very perceptible quantity of ether in the tube, when the electric current could not pass through it without dismissing the ether altogether, and dropping back into the difficulties out of which it has in many cases lifted us. The evident fact that the ether cannot pass through glass freely, and therefore cannot carry electricity with it, may be disputed by referring to the free passage of light, and also of heat, through glass and other substances, in virtue of trans- parency and diathermancy, two terms that have the same meaning, at least, as nearly as that light and heat mean the same thing ; but we believe that this free passage, instead of invalidating our reasoning, only tends to prove that the ether is a material substance ; because, if it is not, it might pass through transparent bodies just as easily as light and heat do. Of course, this belief obliges us to show how light and heat do pass through a transparent body such as glass, and the mode is exactly the same as of heat passing through any other body that is a conductor of heat. Glass is a substance that is known to be a bad conductor, but it is also known that it is not an absolute non-conductor of heat ; therefore, there is no difficulty in supposing that it, and its companion light, can be conducted through glass with velocity propor- tioned to its thickness. We know that in the case of a pane of glass in a window it is practically instantaneous, but that does not mean that it is absolutely so. We know also, that in passing through, both are refracted, and that comparatively little heat is imparted to the glass, even under bright sunshine, which may be very well accounted for by the ether on the other side of the window pane carrying them (light and heat) off, in the same direction they were going, quite as fast as they could be conducted through the glass. But, supposing there was no ether in the room to which the window gave light, or gas, or elementary matter of any kind a condition which could be obtained by making the room of glass and pumping out its contents as was done with the vacuum tube What would be the result ? There would be no wave motion to carry on light and heat into the room, and it would 240 New Theories in Astronomy. be in the same state as the exhausted tube, except that there would be no electricity in the room no current being passed through it -nor anything in sufficient quantity to be lighted up if there was ; the light would be stopped and reflected back from the glass, and nothing inside the room could be seen ; not even that it was dark, because there would be no electricity to make dark zones visible. The window, or rather the whole room, would become a many-sided mirror, for rea- sons almost identical with those that account for a sheet of glass being made into a mirror. We confess that all these deductions have startled us, but we can see no flaw in the reasonings which have led to them. If it is not for want of ether in sufficient quantity at least and the admission of variable quantity is to admit that it is a material substance, that electricity will not pass through a highly exhausted tube, we cannot imagine what can be the reason why it does not ; simply accepting it as a fact is by no means satisfactory. In the dilemma between renouncing the ether altogether or acknowledging its disappearance effective at least it occurred to us that it might be for want of heat, and that in terms of the inter-dependency of temperature and pressure in a gas, heat disappeared in proportion to the decrease of pressure in the^air or gas that was being ex- hausted from the tube, or from cold being applied to it from without ; but that notion has already been disposed of by our own work, when we have seen that a gas in a close vessel can be heated or cooled; to any degree, altogether independently of pressure. When, acknowledging that the ether ought to have some temperature as well as density, we have said that it might have the temperature of vibration whatever that might be, thereby admitting that we could not pretend to determine what it is ; nevertheless, we may take a look at it from a distance, and at least see what it cannot be, anywhere within the limits of our system. We have shown, at page 220, that when the original nebula was about 29,000,000 miles in diameter, its density must have been o 179 that of air at atmo- spheric pressure, and its temperature 225, and that these New Theories in Astronomy. 241 could be neither the density nor temperature of space. With this temperature, then, it is evident that there was still heat enough and to spare in the ether considering it to be a material substance to cause it to vibrate and perform its assigned offices ; and, therefore, it could not be for want of heat that neither it, nor light, nor electricity could be carried through the vacuum tube, but for want of the ether in due quantity ; consequently, the temperature of vibration cannot be so great as 225. Turning back now to page 129, we find the density of the ether estimated at \ th of an atmo- o & o *.o U u sphere, which corresponds to an absolute temperature of 0*000052 or 273*999948 ; but on the following page we expressed our opinion well founded, we believe that the estimate was too high, i.e. too dense, and that it might be 2, 3, or 4 times, or more, too great. Be this as it may, we can see that if the ether alone occupies space beyond a comparatively very limited distance from any body belonging to the solar system it must be almost absolutely free from temperature of any degree, for the difference between -273-999948 and 274 is virtually nothing ; or it must have a special tem- perature derived from the collisions of its own atoms, or from the sun. We have said more than once that the temperature of space cannot be so high as minus 225, and now we cannot believe that it can be so low as absolute zero, because the ether in it is credited with the motion of vibration, which must be either the cause or effect of heat. What then shall we say ? We can only speculate. We can suppose that when the chemical elements were created, or evolved by some process, and began to attract each other, they had the ether to carry them into collision and produce heat ; and that it, being also a material substance, became heated to the same degree as the other matter, always increasing in proportion to its state of condensation, the ether mixed with the other matter being also, of course, condensed. Then, following up this supposition, we can see that when the sun came to be condensed to its present state, the ether must have had the same degree of heat as itself at its surface, and be of the same density as it would in our air at the earth's K 242 New Theories in Astronomy. surface condensed to the pressure of nearly 28 atmospheres ; knowing as we do that the attraction of the sun at the surface of its photosphere is almost 28 times greater than that of the earth at its surface. Under this supposition, therefore, the ether might emit light just as surely as any other matter that may exist, or can be seen, in the corona or atmosphere of the sun, and might be the cause of the Zodiacal Light, probably more naturally than any other cause that has been imagined for it. Mr. Proctor, in his " Sun," has given us a most elaborate description of how the Zodiacal Light could be produced by the swarms of meteorites and meteors, that are generally supposed to be floating around the sun and continually showering in upon it, and we confess that his reasoning is very plausible ; but it, along with other similar hypotheses, has one very serious defect which it is hard to get over, under our existing ideas about matter and its origin. If there is a constant rain of meteorites and meteors falling into the sun now, and the same has been going on during the multitude of millions of years that it is supposed to have existed, we have to acknowledge that it must either come to an end some day, or that there is going on a constant creation or evolution of matter to keep up the supply. It will not suffice to accept the hypothesis that the supply comes from other suns, or any idea of that kind, because each one of them would finally find itself alone with its planets, etc., if it has any, in its domains the same as our sun. Neither would it suit the ideas of those who consider that matter has existed from all eternity and has made itself into all sorts of bodies or systems to suit them. Without continued creation, or evolution, matter must end in condensation into one mass. There can be no self-evolution to keep up the supply of matter. It would require another and exactly opposite power to unmake the final mass, and another change to original matter to start anew on the old course. But we are speculating too soon. It may be said that if the Zodiacal Light is caused by the ether, and if the ether is a material substance, it must be exhausted sooner or later, New Theories in Astronomy. 243 just the same as all other matter and the whole universe to one mass the same as before ; and also that we have no authority for supposing that the ether can be heated and cooled or condensed and expanded. But we think that with what we have done in this chapter, and what we will be able to show in the following one, we shall be able to get over all these difficulties, and also show how the universe might be dissolved and renewed by the ordained process of evolution. R 2 244 New Theories in Astronomy. CHAPTER XIV. PAGE 244 The ether considered and its nature explained. Further proofs given by Dr. Crookes's work, of its material substance. 246 Highest vacuum yet produced. Absorbents cannot absorb the ether. 247 Dr. Crookes's definition of a gas. Not satisfactory. Why. 248 A fluid required to pump matter out of a vessel. 249 Gas as described by Dr. Crookes would not suit. 250 The ether the only elastic fluid we have. The only real gas, if it is a gas. 250 A possible measure of the density of the ether. 251 Causes of dark and light zones in high vacua. 252 The real conductor of light in a high vacuum. 254 How a vacuum tube glows, when electricity passes through it. 255 Conclusions arrived at through foregoing discussions. 256 Some exhibitions of light explained. 257 Gases can be put in motion, but cannot move even themselves. 258 The ether shown to be attraction. And primitive matter also. 259 All chemical elements evolved from it. Its nature stated. 259 Action at a distance explained by the ether and attraction being one and the same. THE idea that the ether can be pumped out of a tube of any kind, along with the air or gas that has been shut up with it therein, will very probably be declared to be absurd, by reference to Dr. Crookes's experiments with his Radiometer, and investigations into the nature of radiant matter ; but when duly considered his work seems to confirm it, and our reason- ings in support of it, in a very convincing manner. Radiant heat, or light, is shown, no doubt, to penetrate into an exhausted bulb and to cause a radiometer to revolve, but we have to consider what is the state of exhaustion at which its force is shown to be greatest, and why that force decreases rapidly when the exhaustion is progressively increased beyond a certain point ; for a certain amount of exhaustion is required first of all to diminish the resistance of the air or gas to the vanes of the radiometer, before the radiant heat gathers force enough to make them revolve at all. Its greatest power to New Theories in Astronomy. 245 produce revolution is shown to be when the exhaustion is at from 30 to 60 millionths of an atmosphere, according to the gas or medium in the bulb see " Engineering," Vol. XXV., page 155 and decreases from that point, often rapidly, as the exhaustion is increased, till at last it ceases altogether. Every- body who has taken any interest in the subject, knows that Dr. Crookes has exhausted radiometers to such a degree that they could not be influenced by the radiation of a candle placed a few inches from the bulb. We are not told at what degree of exhaustion this took place, nor at what degree repulsion, by radiation of heat, is supposed to have ceased altogether, but that does not matter, even though it should only cease when the vacuum comes to be absolute most probably a stage to which it is impossible to attain. What concerns us is the fact that repulsion by radiation does reach a maximum at a cer- tain degree of exhaustion, and then falls off as the exhaustion is increased ; and what we have got to consider is what is the cause of the falling off. We are told it is caused by the attenuation of the matter, gaseous or material, contained in the bulb, and we are satisfied with the explanation. But in order to be thoroughly so, we must insist on believing that it is part of the whole of the matter that has been operated on ; not only of the gas and other matter to the exclusion of the ether, but of the whole, ether and all. If the ether is left behind intact, it must perform the offices it was created for by the imagination of man, or man must discard it altogether. If it ceases to carry light and heat through a vacuum, it is of no more use than we found it to be in the case of electricity, and man is bound to dismiss it as a useless operative, who will strike work for no reason whatever. Some people have sup- posed the ether to be an absolute non-conductor of electricity, because it does not convey that agent through a vacuum. Will they also declare it to be a non-conductor of light and heat? If they will not, then they and we presume every- one else must admit that it can be pumped out of a bulb, in the same way as a gas or any other fluid matter. Here we are led into another consideration, viz., whether the ether is exhausted from a receiver by pumping alone, or 246 New Theories in Astronomy. by the help of absorption. In his lecture, "On Radiant Matter," delivered at the British Association, at Sheffield, August 22, 1879, Dr. Crookes said : " By introducing into^the tubes appropriate absorbents of residual gas, I canj.see that the chemical attraction goes on long after the attenuation has reached the best stage for showing the phenomena now under illustration, and I am able by this means to carry the exhaustion to much higher degrees than I get by mere pumping;" and that when working with absorbents: "The highest vacuum I have succeeded in obtaining has been 20 ooo ooo *k ^ an at "iosphere, a degree which may be^better understood if I say that it corresponds to about the hundredth of an inch in a barometer column three miles high." (We quote from " Engineering," Vol. XXVIII., page 188.) Now, what are we to think ? Are we to suppose that the ether was in part removed by the absorbents ? We think we are justified in saying that the absorbents had not anything to do with the exhaustion of the ether, because Dr. Crookes used different kinds of absorbents for the different kinds of gases he dealt with, and it is hard to believe that all the media he used were equally effective in absorbing the ether as they were with the gases. On the other hand, if we consider that the pumping was the only agent in removing the ether, we ought to acknowledge that it must have been more effec- tive with regard to it than to the gases before absorption was resorted to with them ; or that a stage had been reached at which the pump could not extract any more ether from the bulb. We shall have more to say of this presently. It is a difficult matter to determine, but there is one thing we can see clearly ; when the exhaustion of the bulb was raised to 20 ooVwo** 1 ^ an atmosphere, the density of the ether of itself must have been at a lower degree than that. Consequently if we assume its normal density to be . * cnn th of an atmosphere, in terms of the estimate we Oi^o^ioUU quoted from " Engineering," it must have been diminished to less than one-fourth of that when the above high vacuum was obtained ; because it must have been the density of the residual gas, or matter, and of the ether, added together New 77ieories in Astronomy. 247 which amounted to goToVooo^^ 1 ' t ^ ie same as we argued with regard to the solar nebula when at 6,600,000,000 and 29,000,000 miles in diameter. One thing leads to another, and we have again to repeat our question What is a gas ? And all the answers we have been able to get to it hitherto have been far from satisfactory. A little earlier in the same lecture, referred to a few pages back, Dr. Crookes, after telling us, very elaborately, what would have been the definition of a gas at the beginning of this century, goes on to say : " Modern research, however, has greatly enlarged and modified our views on the construc- tion of these elastic fluids. Gases are now considered to be composed of an almost infinite number of small particles or molecules, which are constantly moving in every direction with velocities of all conceivable magnitudes. As these molecules are exceedingly numerous, it follows that no mole- cule can move far in any direction without coming in contact with some other molecule. But if we exhaust the air or gas contained in a close vessel, the number of molecules becomes diminished, and the distance through which any one of them can move without coming in contact with another is increased, the length of the mean free path being inversely proportional to the number of molecules present. The farther this process is carried, the longer becomes the average distance a molecule can travel before entering into collision ; or, in other words, the longer its mean free path, the more the physical proper- ties of the gas or air are modified." Of course, what we have looked upon as Dr. Crookes's definition of a gas, ends with the second sentence of the above quotation, and is far from being sufficiently complete to be satisfactory ; but we have continued to quote from the lecture, because it contains matter which demands consideration, and helps very powerfully to support the conclusions we have been arriving at. Why the definition is not satisfactory, is that it does not tell us what there is in the spaces between the molecules of what is called the gas. If there is room for them to move in every direction there must be spaces between them, and these 248 New Theories in Astronomy. spaces must either be absolutely empty, or filled with some- thing. If they are supposed to be empty, then the molecules being actually small pellets, like diminutive marbles, or snipe- shot, we immediately begin to think why gravitation does not make them, being ponderable bodies, fall down to the bottom of the bulb ; and seeing that, by the definition, they are evidently considered not to do so, we think of what can keep them from falling, and of how they can be pumped out of a bulb or any sort of vessel. If we fill a vessel with marbles, snipe-shot, wheat flour, or dust, and set a pump to work on it, we shall find that we make very little progress in pumping them out of it. At first we might extract a puff or two of flour or dust marbles or snipe-shot by no means carried into the pump by any air there might be mixed with them, but that would very soon come to an end ; besides, there would be air, gas, something, in the interstices if any of the flour or dust to drive them into the pump when a vacuum was formed in it, and the puffs would cease when the air, which would be in exceedingly small quantity, was all extracted. But independently of all this, we have supposed the spaces between the gas pellets or molecules to be absolutely empty, and there would be nothing to push them into the vacuum created in the pump. There is no possibility of pumping marbles, sand, flour, or dust out of a vessel without the assistance of a fluid agent of some kind, water, gas, or air ; and even then it would be done with much difficulty. Let us, then, suppose there is some such agent filling the spaces between the atoms of the gas and think of what it must be. Were we to ask the question we have a strong suspicion the first impulse of many people would be to reply With gas of course. But this reply could not satisfy us. We should immediately be led to think of that gas also con- sisting of atoms with vacant spaces between them filled with something some more gas ; and were we to follow up that thought through a sufficient number of stages, it is easy to see that in the end the whole space occupied by any gas would come to be filled up with its own solid atoms, without any empty spaces between them through which they could New Theories in Astronomy. 249 move ; and so rendered quite incapable of pushing each other into a vacuum formed by any pump that might be applied to extract them from any vessel of any kind ; or we must sup- pose that each particle would fly of its own good will into the vacuum made by the pump as it were on the wings of the morning. But we recall to memory that the wings of the morning do not always carry us to rest, and we see that filling the spaces with gas would only end in choking up the vessel altogether. It might be said : Nobody imagines that the molecules of the gas in the spaces would be sufficient to fill them up altogether ; and then we have only to ask, What then would there be in the spaces between the molecules of these successive gases to prevent the whole of them from gravitating to the bottom of the vessel ? And to add that there would still be empty spaces left, absolutely empty, that would have nothing in them to help in any way to force the molecules or atoms of any gas or vapour into a vacuum any- where. It is clear then that a gas, such as Dr. Crookes has described a gas to be, could only end in filling the spaces left between its molecules or atoms. It would be an obstruction to their collisions and bombardments which form an essential part of the description or definition. We must, therefore, have recourse to something else for filling up the spaces between the molecules of a gas, and the only thing we can lay hold of is our limited liability agent the ether, which we allow to do all we want it to do and nothing more. Vapours of solid or liquid matter would be of no use, for they would only condense into solid or liquid matter ; unless always maintained at their temperatures of evaporation or ebullition, and that would at the best be only another form of a gas nobody would use a liquid to assist in pumping air out of a vessel and, besides, we should still have to show what keeps their particles apart, what fills the spaces between them, which would force us to appeal to the ether as the only source, just as before. If there are no spaces between the particles there can be no vapours. If by pumping air out of a close vessel the number of its particles is diminished, and we acknowledge that the ether 250 New Theories in Astronomy. pervades all space and matter, in a greater or smaller degree, then we must either recognise that a pump is able to separate the particles of the air from the ether which pervades it in the vessel, and extract them alone ; or we must acknowledge that along with the particles of the air, the pump extracts a corresponding portion of the ether. Which of these two consequences of the pumping we have to choose cannot for a moment be doubtful. It would be as reasonable to suppose that we could pump the colouring matter out of a pond of muddy water, or the mud itself, and leave the clear water behind, as to suppose that the molecules of air, or of a gas, could be extracted from a close vessel, by a pump, and the ether left behind in it. We have called attention two or three pages back to the fact that a fluid agent of some kind is required, in order to be able to pump matter of any description out of any kind of vessel. For solid matter a non-elastic fluid will suit, but for gaseous or vaporous bodies an elastic fluid is required ; but we have just seen that what have hitherto been considered to be elastic fluids, that is, gases and vapours, have no elas- ticity whatever of their own, but are undoubtedly and in reality solid matter ; and that in order to become elastic fluids they have to be mixed with the ether, or something that has yet to be discovered, invented, or imagined. If, then, until such a body is found we take the ether as a substitute, we have to acknowledge that it must be not only an elastic fluid but a material substance, capable of being compressed and expanded, and heated and cooled ; for nobody could conceive clearly the existence of an elastic fluid that is not subject to these conditions. He could not understand how the molecules of a gas could be contracted, expanded, heated and cooled in a vessel, while the elastic fluid which gave them liberty to move or to be moved, remained constantly at one density and temperature. Furthermore, until such a sub- stitute is found, we have to acknowledge that it is the only thing we have any idea of corresponding to a gas as described by Dr. Crookes ; that is, a multitude of molecules colliding with and bombarding each other or their prison walls. But New Theories iu Astronomy. 251 even beyond this we can uphold it to be the only real, in- dependent gas there is ; because, being an elastic fluid, there is no necessity for there being empty spaces between its molecules, or even having molecules in the common accepta- tion of the term. We have no reason to think that there are empty spaces between the molecules or particles of india- rubber ; and if there are, the ether is the only substance we can properly conceive them to be rilled with. The law of Avogadro is, that " Equalfvolumes of gases and vapours contain the same numbers of molecules, and con- sequently that the relative weights of these molecules are proportioned to the densities." Therefore we must always bear in mind that it is the weights, not the volumes, which are equal, and that the volumes may be very different. On this earth of ours, then, we may say with certainty that an atmo- sphere of gas is composed of a definite number of its special kind of molecules, mixed with a definite quantity of the ether, in such proportion that the sum of their densities shall be equal to the density of the air, at atmospheric pressure at sea level, and at o of temperature. Holding this belief, we can see that each molecule, or rather atom, of each gas must have its own amount of displacement to enable it to float in the ether with which it is mixed. This would account in the most satisfactory manner for the diffusion of gases, whereby any molecule, or atom, may float wherever it is driven by collisions with its neighbours, be it above, or below, or on a level with, a molecule of a lighter or heavier gas. Therefore, were it possible to determine with sufficient accuracy the dimensions of the atoms of all gases, perhaps even of a limited number of them, it would be possible to calculate the real density, or specific gravity, of the ether. We have not forgotten that when, by pumping, the ether was reduced to at least one-fourth of its normal density, its buoyant power would be reduced in the same proportion, nor that, when in a state of rest, the displacement of a molecule, which enabled it to float in the ether, would not be sufficient to make it float at one-fourth of that density ; but it might be supposed that when so far relieved from pressure, the molecule 252 New Theories in Astronomy. could expand in proportion to the relief, especially if its form were that of a vortex ring, or of a hollow sphere. However, should this supposition not be admissible, we shall see pre- sently that it is not necessary. We know that as long as any degree of heat remains in a gas collisions of its molecules will continue, dependent on their attraction for each other, which may drive them to any part of the containing vessel ; and that it can only be when they are cooled down to the absolute zero of temperature that they can come to be at rest. But as we believe that the ether can never be reduced to this absolute absence of temperature, nor completely extracted from any vessel, we cannot acknowledge that the molecules of any gas, left along with it in the vessel, could ever come to be absolutely at rest, even although the molecules did not increase in volume with the diminution of pressure. And we think this conclusion will agree with the opinion of Professor Tait, expressed in the quotation, made at page 232, from his work on " Heat," where he says : " In fact, if the kinetic gas theory be true, a gas whose volume is immensely increased, cannot in any strict sense be said to have one definite pressure throughout." This, of course, is tantamount to saying that the diffusion of gases cannot continue to be always exactly regular at extremely low pressures, and must vary as the vacuum is increased ; so that the volumes of the atoms and consequent displacements may continue always the same under all pressures. We see, then, from this quotation, that in all probability the molecules of a gas are not always equally buoyed up by the ether in a high vacuum ; which very likely is the reason why there are dark streaks in it ; streaks without any visible molecules of gas in them, because the ether was not dense enough to keep them afloat. We have still something to add in support of what we said, at page 238, of glass not being pervaded by the ether, in the common acceptation of the word, and of our acknowledging that the ether might, in the course of time, ooze through it and fill up the bulb again, while air, gas and dust could not so ooze through it nor even the larger particles of the ether ; should we be forced to acknowledge that it consists of particles. New Theories in Astronomy. 253 In one of a series of articles in "Engineering," Vol. XXV., on Repulsion from Radiation, we find, at page 155, what follows : "With the same apparatus, Mr. Crookes conducted a long series of experiments for determining the conductivity of the residual gas to a spark from the induction coil. In air he found, at a pressure of 40 millionths (^I^th) of an atmo- sphere, which will be seen from the diagram, is the pressure at which the force of repulsion is at a maximum, that a spark whose striking distance at the normal pressure of the atmo- sphere is half an inch will illuminate a tube whose terminals are 3 millimetres apart. By pushing the exhaustion farther, the half-inch spark ceases to pass, but a one-inch spark will illuminate the tube, and as a vacuum is approached more electromotive-force is required to force the spark to cross the space separating the terminals within the tube, until at still higher exhaustion a coil capable of giving a 6-inch spark in air at the pressure of the atmosphere is required to show any indication of conductivity in the residual air. It was found, however, in experimenting with so powerful a spark that occasionally the glass was perforated by the discharge taking place through the bulb ; but it is a remarkable fact that the perforation in such cases was so excessively small that several days were occupied before equilibrium of pressure was estab- lished between the inside and outside of the bulb." Here we notice first and it was the reason why we have made the first and longest part of the quotation that the spark whose striking distance was half an inch at the normal pressure of the atmosphere, fell to under one-fourth of its power in a vacuum of only J_ th of that pressure ; that when a one-inch spark was required to illuminate the tube, it must have decreased to one-eighth in a vacuum of ^-J-Qoth ; and, if it be admissible to follow the same proportion, the 6-inch spark must have been exhibited in a vacuum of i 250000^ ^ an atmos phere at least. Perhaps all this ex- periment was carried on in vacua produced by pumping alone, and the final vacuum may have reached a greater height than that which we have just mentioned ; but the most interesting part of it is the perforation of the bulb by the 6 -inch spark. 254 New Theories in Astronomy. In it we have to consider what was the conveyer which carried the electric spark through the glass of the bulb, instead of to the other terminal of the coil so close at hand, and it is a very difficult problem to solve. We naturally recur for some solution to the stratification of light given out when an electric current traverses a gas at very low pressure and gives rise to zones alternately light and dark as noted in the reference we made, at page 229, to Professor Balfour Stewart's experiments. We cannot think it unreasonable to suppose that the dark zones contained no matter at all that could be lighted up, and that it was the lighted zones alone which contained carrying matter for the electricity. If so, we can easily imagine one of these zones or strata carrying the perforating spark from the induction terminal to the nearest part of the glass of the bulb, for it was as possible for it to lie in that direction as in the direction of the other terminal, and the difference of distance between the first terminal and the glass, and between the two terminals, would not be so great as it appears to be on simply reading the accounts of the experiments ; but we have still to think of how it managed to force itself through the glass of the bulb. To get over this difficulty, we can refer to what we have said, that is, that glass may be thoroughly pervaded by the ether in an almost infinitesimal degree, and suppose that the electricity may have discovered, or rather been led to, the ether contained in the glass tube or bulb, and so found its way to one of the oozing holes we have said might exist in the glass; even the oozing hole may not have passed quite through the glass, and there might remain a very thin film to be burst open before perforation was complete. Also we may note that the zone which performed the office of carrier to the side of the bulb was much more probably composed of resi- dual ether than residual air or gas, or at the least formed a preponderating part of the carrying element. The fact of the hole being so minute " that several days were occupied before equilibrium of pressure was established between the inside and outside of the bulb " on such occasions, goes far to prove that the carrying agent through the glass must have been the New Theories in Astronomy. 255 natural carrier of electricity, light, and heat. We cannot conceive that an eruptive force could open such a small passage through the glass of the bulb, but we can conceive that it should be able to force itself through a very minute passage already open, and even join two or more such passages into one. This conception makes us think of the many oozing passages there may be through a glass bulb ; passages so minute that the ether might pass through them, but nothing so gross as any of our known gases ; in fine, so minute that glass, for all the compact look it presents to us, may be only as a very fine sponge in respect to the ether. However, that the perforations related in the above quotation were large enough for air to pass through them there can be no doubt, otherwise the equilibrium between the pressures on the inside and outside of the bulb could not have been re-established even after many days ; for there still remains the idea that the oozing holes might be so small that nothing but the ether could pass through them. Should the glass of a vacuum tube or bulb be pervaded by the ether in the manner we have supposed it to be, and we believe there can be no doubt that it is so, it is obvious that its glowing when a current of electricity is passed through it must be caused by the electricity and consequently of its light, being carried into the body of the glass by means of the ether imbedded in, and forming a constituent part of, it. In connection with this we have to remember that the air in the tube does not glow when it is at full atmospheric pressure, but only when a certain degree of vacuum has been produced in it ; and therefore it is equally obvious that it is only when the ether enclosed in the tube is reduced to the same degree of tenuity as that imbedded in the glass forming the tube, that the light of the electricity can be carried by it into the glass and make it glow. But to show this more clearly, it is necessary to refer to the steps by which we believe we have made very plain what must undoubtedly be the nature of the ether. (i) First of all we have shown that, if there be such a thing as the ether, it can be pumped out of a close vessel of 256 New Theories in Astronomy. any kind ; which proves that it must be a material substance, and in consequence can be expanded, or rarefied, and com- pressed the same as any other material substance ; and that if there is no such thing, something else, having these qualities, has to be invented to take its place. (2) In showing this it has been made abundantly clear by the example of the hair of a cat in variable weather, to which we may add the exhibi- tion of lightning in daylight, that it cannot make electricity visible, or illuminate any matter, unless the quantity of elec- tricity it has to carry bears some certain proportion to the density of the ether in the matter that is illuminated. (3) In proof of this we have shown how, through its carrying power it can convey electricity of adequate force up to very great heights, so as to illuminate very rarefied air and cause auroras ; the conveying being done either directly from the earth or by means of the ether mixed with the air carried up by whirl- winds to those great heights ; and (4) how electricity is carried into the body of a tube of glass and makes it glow. With these examples we can extend our ideas to other exhibitions of light, which, otherwise, we could hardly avoid looking upon as mysterious. We can see how marsh gas, rising up from boggy ground, becomes mixed with common air till it reaches a certain density, and forms the Will-o'-the-wisp when there is sufficient electricity in the air to make the diffused marsh gas visible, through the medium of the ether always mixed with it ; or, perhaps, rather when the density of the diffused gas corresponds to the density of the ether. Then we have the phenomena of films of matter on the sur- faces of certain liquids glowing with appropriate colours ; which films must be pervaded by the ether in proportion to their conducting powers, the same as we have seen must be the case with all kinds of matter, the light given off corre- sponding as is natural to the composition of the films ; and of course this same reasoning, or exposition, applies to the films formed on, or near, the surface of the sea which produce what sailors call " fire-on-the-wave." Lastly, and akin to the glowing caused in a vacuum tube, we cite the case of the glow-worm, the radiation from which must of necessity contain a certain New Theories in Astronomy. 257 amount of the ether in it, and may either glow constantly or intermittently according to its capacity for carrying electricity or light of any kind, constant or inconstant. Or if there is no radiation from it, its skin may possess the properties of a film on the surface of a liquid. We have seen in the " Times " of September 21, 1896, in its report for that day of the Meeting of the British Association at Liverpool, that in experimenting with glow-worms Dr. Dawson Turner had found some diffi- culty in getting them to glow when he wanted, but found they gave off the radiation whether glowing or not. Perhaps his interference with them destroyed the balance of force between the electricity present and the density of the ether in it with- out stopping the radiation. Hitherto the light given out by a nebula, and any light of the kind not easily accounted for, has been attributed to incandescent gas not burning or being consumed, but only glowing. Now it is time to look upon it as belonging, at least in part, to the ether, and to look upon the bright line in the spectrum of a nebula as the Ether Line. We shall have to return to this later on. We said, at page 248, that a fluid of some kind, elastic or not elastic, is necessary to enable us to pump solid matter out of a vessel of any kind, and went on to show that a gas as described by Dr. Crookes, or that can be described, in its own independent state of existence, by anybody, could not supply the want ; because it consists of particles, molecules, atoms any name that can be given to them which have no power in themselves to move or to give motion to anything ; they can be moved but cannot impart motion to anything, even to one another, until they are first set in motion by attraction. This in its turn led us to see that the only elastic fluid we have is the ether, and our work since then has taught us that we were wrong in saying at page 250 that a non-elastic fluid would suit for pumping solid matter out of a vessel ; for we now see that what we have been in the habit of looking upon as non-elastic fluids, must owe their fluidity, such as it is, to the ether, which, in proportionate degree, pervades them the same as it does all other matter. In this way we are run S 258 New Theories in Astronomy. down to the only conclusion we can come to, namely, that the ether is the only connecting medium and carrying agent of matter that we have, or even initiator of motion, except attraction ; and being matter of the nature of an elastic fluid, there is no reason why we should not at once consider it to be attraction itself. It has been looked upon, for no one can exactly tell how long, as the connecting mechanism of the universe, thus having, in reality, assigned to it the attributes of the law of attraction, and all that we have to do is to put it in its right place. We are, in a manner, taught to look with suspicion on two agents being required to do one kind of work, or even two kinds of work that are so closely allied that we cannot separate them in a way that satisfies us ; and this is precisely a case in which we can have one agent that can connect matter, and at the same time carry immaterial elements from one place to another. Having got this length we have still to go one step farther. We cannot now doubt that the ether is a material substance, and if it is, there is nothing to prevent us from considering it to be the primitive matter ; in fact it would be absurd to look upon it in any other light. We cannot conceive of anything having been created before the ether, or ordained before the law of attraction, and thus we have the two coeval and one. It is long years since physicists, chemists especially perhaps, began to think that the great number of chemical elements cannot all have existed from the beginning of things, and that it is far more probable that they have all been evolved from one primitive substance, and this idea must now be gathering more strength from day to day in view of the new elements that are being constantly discovered ; the unknown is being made known, and the air we breathe instead of being one in four elements, as in former times it was considered to be, is now not far from double that number in one. Adopting this notion, then, the ether is much more likely to have been the primitive element than any other material substance that can be thought of. If it has never been thought of in this light, it has come to be very remarkably near it, as may be seen by referring to the long quotation we made in Chapter New Theories in Astronomy. 259 VII., beginning at page 129, where the idea of the ether being the connecting medium of matter is made use of to compute its density. Little thought we of this when we made the quotation, but there was the idea whether the author saw or not all that was implied in it. Having broached the notion of the ether being the primi- tive element of the universe, or at all events, of the solar system, we might be expected to show how all the other elements were formed from it ; but that has been done for us in a very much more able manner than we could have done it. Anyone who chooses to refer to " Nature " of Septem- ber 2, i886, ; will find in Dr. Crookes's opening address, on Chemical Science in Section B, at the meeting of the British Association for that year a very detailed explanation of how all the chemical elements might have been elaborated from one that he called Protyle ; in which explanation he will only have to change this word into Ether to comprehend the pro- cess much more easily than by any exposition we could pretend to draw up. To quote the whole address would be altogether out of place, and besides, our notes of it are only fragmentary. But for present satisfaction of those who cannot immediately refer to " Nature," we may say that in the same report it is clearly stated that Sir George B. Airy was of opinion that all bodies may not be subject to the law of gravitation ; and have no cause to think it strange we do not see that, were the ether and attraction one and the same, the whole universe would be finally collected into one mass, itself included. They will have better authority than ours for believing that the ether may connect matter evolved from itself, without being materially confounded with it. At the same time we acknowledge the necessity for expressing our idea of what we consider to be its nature, and in compliance with this obligation we say we have conceived it to be of the nature of indiarubber, not an elastic fluid as we have called it before, but rather an elastic substance like a jelly, as some people have conceived it to be ; not a gas, because it does not require any medium to connect its particles. Looking upon it in this light, action at a distance can be S 2 260 New Theories in Astronomy. accounted for in a very natural manner. When a stretched indiarubber band is relieved from strain, the relief must be felt instantly throughout every part of its length ; for, although the band may take time to contract, no time is re- quired for the relief from strain being felt. In like manner an alteration in strain between the sun and the earth and these alterations of strain are taking place every instant connected by an indiarubber ether will be felt instantly in both bodies ; and should anyone stand out for time being required to con- vey the attraction, let him remember that the difference of its power would be felt first at the two ends of the connecting medium, for the very good reason that even attraction itself could not prefer one extreme to the other. And that is all that is meant by action at a distance. Here are some other things that could be explained more easily than they can be at present, through the ether and attraction being considered to be one and the same, than under any other conception we can form ; but although we have a dim vision of such explanations in some cases, our knowledge of the sciences involved in them is not sufficient to warrant us in letting our dim conceptions see the light. Therefore all that remains for us to add is, that some things we have said of the ether may have to be so far modified now, but as they have had their part in leading us to the conclu- sions we have arrived at, they cannot be altogether sup- pressed. New Theories in Astronomy. 261 CHAPTER XV. PAGE 261 Construction of the solar system. Matter out of which it was formed. 262 Domains of the sun out of which the matter was collected. 263 Stars nearest to the sun. Table VII. showing distances. 265 Remarks on Binary Stars. Table VIII. showing spheres of attrac- tion between the sun and a very few. 266 Sirius actually our nearest neighbour. Form of the sun's domains of a very jagged nature. 267 Creation of matter for the nebulae, out of which the whole universe was elaborated. Beginning of construction. 267 The law of attraction begins to operate through the agency of evolution. 268 Form of the primitive solar nebula. The jagged peaks probably soon left behind in contraction. 269 How the nebula contracted. Two views of the form it might take. Comparison of the two forms, solid or hollow; 272 The hollow centre form adopted. The jagged peaks left behind. 273 The nebula assuming a spherical form. Shreds, masses, crescents separated from one side. 274 Probable form of interior of nebula. Compared with envelopes in heads of some comets. 275 Reflections on the nebula being hollow. Opinions of others quoted. 276 The matter of a sphere solid to the centre must be inert there. 277 Further proofs of the nebula being hollow. 278 How rotary motion was instituted. 279 Such a nebula might take one of two forms. 280 The form depending on the class of nebula. Planetary in the case of the solar system. A similar conception of how rotary motion could be instituted. IN this chapter we proceed to consider how the original nebula was formed, and whether the solar system could be evolved therefrom in the manner shown in the analysis of Chapter V. The usual way of treating the solar system has been to suppose it to have been formed out of a nebula extending far beyond the planet Neptune, generally in a vague way ; although some writers have specified a limit to the distance, in order to give some definite idea of what must have been 262 New Theories in Astronomy. the density of the nebula at some particular period of its existence. In the first part of our work we have adopted the same plan and we mean to follow it out, because it gives us a greater degree of facility for expressing our ideas, and making them more intelligible, than by adopting a new method. But we shall previously endeavour to show where the nebula itself came from and how it was formed, which seems to us to be as necessary as to show how it was transformed into the solar system. We understand Laplace to have supposed the nebula to have been formed out of cosmic matter in its simplest con- dition, and in its most primitive atomic state, collected from enormously distant regions of space by the power or law of attraction. In this we shall follow him, because we do not see the necessity for matter having to be created in the form of meteorites or meteors, or any other form, to be afterwards dissociated and reduced to the atomic state, by heat produced by collisions amongst the dissociated atoms. Surely it would show more prescience, more simplicity of work, and economy of labour, to create matter in this primitive state, than in one which required it to be passed through a mill of some kind, as it were, before it was manufactured into nebulous matter ; in fact, to make brickbats in order that they should be after- wards ground down dissociated into impalpable powder, to render them fit to be worked up into bricks. But our first effort will be to attempt to define the collecting grounds of this cosmic matter, somewhat more particularly than has been done hitherto, as we believe that even a superficial study of them will assist us greatly in forming a more comprehensive idea of the whole solar system than anything we have met with in any of the books which we have had the opportunity of applying to for information. The collecting grounds, then, are clearly the whole region of space to which the attractive power of the sun extends, or what astronomers would call within the sphere of his attrac- tion. These domains, like those of any other proprietor, are limited by the domains of his neighbours. At first sight, it would seem that his neighbours are infinite in number, but a New Theories in Astronomy. 263 little thought will show that the number may be very limited indeed. On this small earth of ours, it is a very common thing for a landed proprietor to be able to look over the domains of his neighbours, and see those of proprietors more remote ; even to look over the domains of his neighbours' neighbours, and see properties so remote that he does not even know to whom they belong nor how they are named. With much more reason, the same must be the case with the sun, more especially as he, from his own mansion-house, sees nothing of the domains, but only the mansion-houses of others, there being no landmarks, hills, fences or woods to cut off his view, as there are upon the earth ; the only interruption possible to his view being that another mansion-house should come to be exactly between his and that of a farther-off neighbour. For our purposes, we will assume that his nearest neighbours are those the distances of whose mansion-houses have been measured, and will adopt the following list of them, taken from Mr. George Chambers's " Hand-Book of Astro- nomy," part 3, page 10, 5th edition, 1889, and forming Table VII. All that we can learn from this table is that the boundary between the sun and any one of the stars mentioned in it must be somewhere on a straight line connecting the two, but that does not furnish us with any information as to the extent of the sun's domains, although it does help to give us some idea of their form. For some knowledge of their extent, we require to know how far the lordship of each one of the proprietors extends from his mansion-house ; which, very much the same as it does upon the earth, depends upon the power he has to take and keep it ; it depends on the mass of each neighbour who actually marches with the sun when compared with his own mass. The list referred to does not help us in any way to determine this, as we have just said, but we have found in Professor Charles A. Young's " Lessons in Astronomy," of 1891, page 270, the masses of six binary stars whose distances, calculated from the parallaxes given in it, furnish us with data from which we can calculate the distance from the sun of the boundary between him and any one of them. The number is very small, but still from them we can 264 New Theories in Astronomy. gain some notion of what was the form of the domains from which the original nebula was collected ; that is, always under the supposition that the sun and his system were evolved from TABLE VII. LIST OF STARS WHOSE DISTANCES FROM THE SUN HAVE BEEN MEASURED, AND WHICH ARE ASSUMED TO BE HIS NEAREST NEIGHBOURS. Star. Magnitude. Proper Motion. Paral- lax. Distance. Observers. Sun's Distance = i. Time of its Light leaching the Earth. o Centauri . . I 3^7 H 0'75 275,000 years. 4*34 Gill. 6 1 Cygni . . 6 5'14 O*5O 412,500 6-51 O. Struve. 21185 Lalande . . 7i 4*75 0*50 412,500 6-51 Winnecke. Sirius I 1-24 0-38 543 >o 8'57 Gill. /i Cassiopeiae . .. .. 0'34 606,000 9-57 O. Struve. 34 Groombridge 8 2*81 0-29 711,000 11*23 Auwers. 9352 Lacaille . . 74 6*95 0-28 737,000 II'62 Gill. 21258 Lalande . . 8* 4-40 0-26 793,000 12-52 Kriiger. 6 Arg. 17415 . 9 1-27 0-25 825,000 13*02 Kriiger. \o Th N O\ to ^ ""> *O ** "J- OO vO 00 00 Tj- "8 3 " vO <-> ON N rON O^OfO sS ^r ^ a .5 O O Q O *^ ""> O 00 O O rj- N M TJ- rf t^- O OO s V 8 8 o oo a j w',3 GO Without, Miles. O Tj- f> vO ro OO ON O\ O N "^ CO ^ f^ w >O rO W OO ** ON rf ro O^ u-> r>. rtf- rr> r^ \O m -i s. '1 O 00 r^ ro N "- ON oo" ON iO TT N 1 o c .S *jj o * ^ ^> c s a '& rt I s !>. ^O rf ro r^ I T3 1 - ui roONOO Q O m m r> oo t~>.i~>.O vovo 3f PS ror^^vr ONOOOOCXJVO Ti-ON.vO CO t- r^ 00 rj- N 1-1 M *- i D 1 ? N HH O 2 d .i O S |i vOOOvOQOOOrh \^ *-O ^o O O co ON t** t^vomvo COONTJ-ON 1 8 S O t> Q.S OOVO f)l^O co>^'4'' OOVO t^vo NOOOO fOt^ LOtOt^ONlOd H M 1 10 ro HH _rt "rt 9 i 00 vO 00 vO 10 10 IO CO OOOQO *** ON vr> O OOJ O O Tj-fON O N rfrJ-t^ONfOOO i O O >, 1 Q Ij TSii 05 .5 \O cOfO-ivO rOfOONVO M3 t^OO O xorOO t-^vo I-HVOCOO MIOI-IIOON Ov^O^--" ? ? fO N" M "8 gOOOOQ-^-t^HH OO'OOOONi^.vo O rJ-ONOO Tj-OOVOvO V 8 8 00 O c O 'bo |J r S NVOVO roN r^.r-.oo to ro^-vO O i-ivO ** iO- t^O^oO N | - 1 ON s & O N s ? Pi 5.s 00 xoOOO O O\v> t>,i-i fOfOWOO ON-00 NOO N. ^O MO. **> "'* 10 to rf i-T ^ u s t-^ ro <& V > M vO rr . | I ft i! 00 VO ' 1 fj 53 ooooooooo OOOOOOO'ONN 1 VO ON < 9 fc s 1 O QOMO"^-NrJ-OrO Ooo t^ri-^O fO^O O vo lovo rot^rl-N vO rj- IN <-> 1 & $ PI "I oo to ; *! i * 5 , 3C5'0 ^^3 1 1 1 1 i ; I ; 1 . 1 J p $ >, < W > 0) C M 3 P & J? S 286 New Theories in Astronomy. idea, more than anything- else, of not increasing the almost unimaginable tenuity of the matter composing the nebula ; and the position of Neptune in the system is so peculiar com- pared with the other planets, that it cannot be properly used as a standard for any kind of inquiry. The result obtained above can therefore be of no use for the investigation we have undertaken. Not only so, but the, almost similar result in the case of Uranus is also rendered useless from the same cause, in which we find that the region of greatest density of the nebula is only I "92 per cent, beyond the orbit of the planet. If the mean distance from the sun of Neptune's orbit had been what was used by Leverrier in the calculations which led to his discovery, namely, 36*152 radii of the earth's orbit, the region of greatest density of the Uranian nebula would have been 14*48 per cent, beyond his orbit, as may be seen from the addition to Table IX., in finding which we have used the same system as in all our work. In the next four nebulae of the table including the one we introduced to represent the Asteroids we see that their regions of greatest density are respectively 19 * 58, 12*47, J 3 ' 5^ and 1 2 63 per cent, farther out from the centre of the sun than the orbits of the planets formed from them. Here, then, we see a very apparent approach of uniformity, and can say with much reason that planets could certainly be formed out of the matter abandoned, through centrifugal force, by hollow nebulae similar in construction to what we have demonstrated that of the original nebula to have been ; each of them occupy- ing the position corresponding to its orbit. Following these come the Earth and Venus nebulae. In the former, the region of greatest density almost coincides with the orbit of the planet, being only cr 15 per cent, beyond it, instead of something like 12 per cent, as it ought to be to conform with the four preceding cases ; and in the latter it is 5 '25 per cent, within the orbit of the planet to be made from it But in this case we have to note that the orbit of Venus is 3*33 per cent, beyond the position pointed out for it by Bode's law, and that it is the only one of the whole number of planets whose orbit is farther removed from the sun than the New Theories in Astronomy. 287 distance assigned to it by that law. Also we see from our reversal of Bode's law, that the rates of acceleration of rota- tion for these two planets are I *88o for the earth and I -626 for Venus, instead of the average of 2-5896 of the four preceding planets ; that the density of Venus is less than that of the Earth, instead of being greater as it is successively in all the other planets from Saturn inwards ; and we may add that the diameters are nearly equal. All showing that influences had been at work in the formation of these two planets, different to those in the preceding four ; and that until we know what these influences have been, we cannot account for any anomalies produced by them. Neither are we called upon to consider that our theory is destroyed by these anomalies, any more than it can be by the anomaly in the case of Neptune's position. Lastly, we have in Mercury the region of greatest density of his nebula at 13*55 per cent, beyond his orbit, and the rate of acceleration of revolution over Venus 2-5543 times, both of which conform fairly well with the same noted facts^ in relation to Mars, the Asteroids, Jupiter, Saturn, and, we may add, Uranus. But, in justice, we must not omit to add that there may be some error in the excess of 13*55 P er cent, in the distance from the sun beyond his (Mercury's) orbit, arising from the fact that there may have been some difference from what we made it to be, in the line of separation between his nebula and that of Venus ; and also that we had to guess at the line of separation between his and the residuary nebula. Moreover, it has to be taken into account that his orbit is 3*22 per cent, within the position assigned to it by Bode's law. From the Table IX., and an examination of it, we learn that out of the 9 nebulae into which we divided the original one, in the analysis of the nebular hypothesis, we have five four of which are consecutive which may have been almost of the same construction, and not far from the same propor- tions ; that the original nebula cannot, for reasons assigned, be looked upon as either similar, or the reverse, to the five just classed ; that one, the Uranian, is practically similar to the five, and might be exactly similar could the anomaly in 288 New Theories in Astronomy. the position of Neptune be explained ; and that the remaining two, the Earth and Venus nebulae, seem to show that they have been abandoned in a manner different from the others. Perhaps we may be able, later on, and in a different way, to give a reasonable explanation of the anomalies in the positions occupied by Neptune, the Earth, and Venus, and also of the peculiarities of their dimensions. So far, we believe we are justified in concluding that out of the 9 nebulae, 6 may really be considered as supporting our theory, and the re- maining 3 as, in all probability, capable of being shown to be, at least, not opposed to it. To this we may add that on several occasions we have stated our opinion, that the divisions between the nebulae we have established, could not have taken place at the half-distance between the orbits of any two planets, but much nearer to the outer one. It is evident, then, that if we had made the divisions at any distance farther out, say at three-fourths of that distance from the inner orbit, the extreme diameter of each one of the nebulae would have been just so much greater, the region of greatest density farther out from the centre of the sun, and even that of Neptune would have been beyond his orbit. All this could be done, yet but it would serve no good purpose, as will be seen presently ; and we might be accused of cooking our data in order to produce a result favourable to our theory. We have made the foregoing examination because, when we began our work, the general idea was that, according to the nebular hypothesis, the material for the formation of each planet was abandoned by the ideal nebula in a distinct and separate mass from any other we are not at all sure, how- ever, that this was Laplace's idea. This, we found out, could not be the case when we attempted to give some sort of separate or distinct form to the matter out of which Neptune was supposed to have been formed ; and when we became convinced that all the matter abandoned by the nebula, from first to last, must have been thrown off in one continuous and, most probably, uninterrupted sheet. This, of course, makes us think of how the division of the sheet into separate rings was brought about, for there must have been absolute separation New Theories in Astronomy. 289 between them, otherwise separate planets could not have been made out of the sheet ; and the only explanation that can be given is, that it must have depended on the quantity of matter that was abandoned, in nearly equal times, at different periods of the operation ; for the areolar law precludes the idea of there having been very rapid changes in the rate of rotation of the nebula, and certainly of its decrease at any period as long as condensation and contraction went on. Whereas, although the sheet thrown off may have been con- tinuous, we have no reason to suppose that it was of constant volume or density from beginning to end of the operation ; in fact, we have already seen that its density was constantly increasing, and have suggested, in the reversal of Bode's law, that the differences in dimensions and densities of the planets have arisen, from irregularity in the quantities of matter aban- doned from time to time. This irregularity could only arise from the mode of construction of the nebula, and from the forms it assumed during condensation, as we shall attempt to show in due time. Meanwhile we can conclude that the region of greatest density in any of our nebulae had no in- fluence whatever on the position of the orbit of the planet that was formed out of it. We have shown, very clearly we believe, at page 109, from quotations at second hand from his own exposition of his hypothesis, that Laplace considered that condensation could only take place at the surface, or in the atmosphere as he called it, of his nebula, on account of its being possible only after radiation into space of part of its excessive heat ; and that consequently there could be no acceleration of rotation in the nebula, due to the areolar law, except where there was condensation. On the other hand, in our cold hollow-sphere nebula, condensation could only take place at the region of greatest density, or greatest mass, which must be always very much nearer to the surface than to the centre ; so that in both cases, equally, the abandoning of matter under the influence of centrifugal force would be virtually the same, and no further remarks are called for, on our part, on that head. U 290 New Theories in Astronomy. Neither is it necessary for us to show how planets could be formed out of the rings abandoned by their respective nebulae, for everybody seems to agree that when they broke up, the fragments could not do otherwise than form them- selves into small nebulae, which in the course of time con- densed into planets. M. Faye's explanations are good for that. With respect to their motions of rotation being direct or retrograde, we have seen, at page 116, and following, that Laplace's description of how the former motion could be brought about is mechanically correct ; and, at page 121, that he did not consider that the direction of revolution of a ring necessarily demands that the rotation of a planet formed from it should be in the same direction. As already said, he has shown how direct rotation could be produced, and we have no doubt that he could have shown how retrograde rotation could also be produced, had he found it to be at all necessary. Be that as it may, however, it is a very simple matter to show how, following our method of construction of the primitive nebula, the retrograde rotation of Uranus and Neptune could, or rather must, have been determined. It will be remembered that when we were " getting up " the original nebula in the domains of the sun, whose form we described as well as our limited means would admit of, we said that when the cosmic matter contained in them began to contract, not only the parts contained in the peaks and promontories would soon be left behind, and come in at a slower rate, but also large masses of the outer part of the main body, especially of what was on the sides opposite to the deep hollows made in the domains by the most powerful of the sun's neighbours, in the form of fragments, crescents, and parts of hollow segments. Let us now, then, suppose the operation of planet-making to have advanced so far that the whole nebula was rotating on its axis, and abandoning matter through centrifugal force, from its equatorial regions in a continuous sheet, as we have said several times that it must have done, and that the matter destined for Neptune and Uranus has not only been abandoned, but divided into two New Theories in Astronomy. 291 distinct rings a supposition made in this case only for facility of description. Then some of the matter which had been left behind, but still being gradually drawn in, would be almost totally intercepted in the equatorial regions of the nebula by these two rings, and would fall in greater quantity upon their outer edges than anywhere else, more especially in the case of the outer one. These adventitious additions would come in without any angular, or tangential, movement whatever, because rotary motion was not yet established in them, and would retard the revolutionary movement of the rings in decreasing degree from their outer to their inner edges while acquiring angular motion themselves ; and would also intensify the original difference in revolutionary motion already exist- ing at these edges. At the same time these additions of extraneous matter would seriously impede the contraction of the rings in the radial direction on account of their volume, but would have little or no effect on contraction in the cir- cumferential direction ; the consequence of which would be that they would break up before friction, and the mutual collisions of their particles, had time to produce a uniform revolving motion throughout their whole breadth ; that is, while their inner edges would be still revolving with more rapid velocities than the outer ones ; and the rotary motions of the planets derived from them would be retrograde, according to M. Faye's demonstration or that of any other who has taken the trouble to think over the matter. And we may add that this mode of reasoning, applied with a little more detail, will very fully account for the rotation of Neptune being more decidedly retrograde than that of Uranus, because the quantity of matter so deposited on the outer flat ring in this process^would unquestionably be greater than on the inner one, and consequently the difference of velocity between the outer and inner edges of the two rings also greatest on the outer one. We take it to be unnecessary even to say that, the revolu- tion of the satellites of these two planets being retrograde and anomalous, the rotation of their principals must be retrograde and anomalous also. U 2 29 2 New Theories in Astronomy. Before going any farther we have something to say about the anomalous position of the orbit of Neptune, which is certainly not the position sought for by M. Leverrier ; in fact, the elements employed by him in his calculations to discover a perturbing planet whose existence may be said to have been known are so different from the elements of the one actually discovered, that there would be nothing out of reason in saying that Neptune is not the perturber that was sought for, but only an instalment of the perturbing force. It may raise a storm in some quarters to say so, but the fact remains the same, or it must be confessed that mathematics is a more elastic science than it professes to be. He has not the power of attraction required to produce the perturbations in the movements of Uranus which gave rise to the search for an outer planet. M. Leverrier made his calculations under the belief that a planet of ^^th part of the mass of the sun was required to produce the perturbations that had been observed in the orbital motion of Uranus ; whereas the planet discovered has only 20 Q OQ th of that mass not one-half of what was required. On the other hand, the semi-axis major of the orbit of the planet discovered is found to be 30*037 instead of 36 ' 1 54 (Bode's law measures) used for the search ; which greater proximity to the sun, it is true, increases its power of attraction I '449 times, but as its mass is only 0*465 per cent. of what was expected, the attractive force would amount to less than 0*68 per cent, of what was required. Then the question comes to be, Where did the wanting 0*32 per cent. of attractive force come from ? And the answer is that some astronomers have been searching for another planet to make up the weight, with more or less diligence, ever since the deficiency came to be recognised. But all that we want to have to do with the question is to suggest a very plausible reason for the anomalous position of the orbit of Neptune. If there is another planet beyond Neptune, the ring (per- haps the rings) out of which he and the others were made, must have been much greater in breadth than what we have assigned to it at page 88, viz. 1,010,000,000 miles ; perhaps even one-half more, as may be deduced from the addition New Theories in Astronomy. 293 made to Table IX., and what we have said in connection with the semi-axis major adopted for the sought-for planet, by M. Leverrier in his calculations. Now, that a ring of such enormous breadth should have held together in one piece, until it finally broke up through condensation and contraction, requires an extraordinary effort of imagination, after seeing what has taken place with the rings of Saturn ; even the breadth of 954,000,000 miles appropriated to the Uranian ring (see page 90) demands an elastic imagination to con- ceive its holding together ; so that the outer ring of the system may very well have been divided into two, as we have said at page 134, and two not very unequal planets made out of it one into Neptune, and the other into one as far beyond M. Leverrier's adopted distance of 36*154, and of such mass as would make up the missing 0*32 per cent, of deficient attractive power. No doubt the outer ring may have broken up into several planets, or even into a swarm of asteroids, but we prefer to think of only two planets ; because it seems to us that to draw Uranus into the position he occupied when Neptune was discovered, the two planets must have been operating in conjunction ; an idea that is not so easily enter- tained when there are several planets, or a host of asteroids, to be taken into account. We have already discussed, at page 115, the mode of formation of the sheet of matter abandoned by the nebula, its posterior division into separate rings, and how the part of these rings from Saturn inwards could revolve themselves into planets having direct motion, so it is not necessary to go over the same ground again, merely because we are dealing with a hollow nebula instead of one full of cosmic matter to the centre. We have also shown, at page 119, that the nebula must have been somewhat in the form of a cylinder terminated at each end by what may be looked upon as a segment of a sphere, although it would more probably be an almost shape- less mass of cosmic matter, because the greater part of it would be very slowly brought under the influence of centri- fugal force as it fell in from the polar directions ; and again, a 294 New Theories in Astronomy. few pages back, that almost all the matter coming in from its equatorial regions even what might be called its tropical regions would be intercepted before it could reach the Saturnian nebula. Likewise, at page 137, when examining Bode's law reversed, we have seen a limit set to the accelera- tion of the movement of revolution in the planets of the system as they approached the centre, because any accelera- tion beyond a certain limit, clearly marked out, would of necessity be within the nebula itself, and the rate of revolution would be less than that of the sun on its axis at the present day. This may be used as an argument against the nebular hypothesis, but we think we have shown in the same FIG. 2. Chapter VII. that this is not the case. But we have still to try to account for the repeated rises and falls in density in the planets from Neptune to Mercury, or even farther ; which operation causes us to bring forward, first of all, a new idea as to what the form of the nebula would come to be. The accompanying rough sketch (Fig. 2), drawn to a scale of one-quarter inch to 1,000,000,000 miles shows that, sup- posing the Saturnian nebula to have been a perfect sphere, and to have abandoned matter till the velocity of rotation came to be equal in a region corresponding to the tropical region of the earth, the cylindrical part of it would present a straight side of more than 1,000,000,000 miles in length ; pro- New Theories in Astronomy. 295 vided always that the general diameter of the nebula did not decrease through condensation and contraction during the operation ; but as this could not be the case the length of the cylindrical part would be considerably less than that. How much less we have no means of calculating. On the other hand we have seen, when discussing, in the case of Jupiter, how matter must have been abandoned by any nebula, that from the time the original nebula began to abandon matter through centrifugal force, it must have gone on acquiring a constantly increasing length of straight side as it contracted. Thus the Saturnian nebula would begin work with the ac- cumulated cylindrical length it had inherited from Neptune and Uranus, so that the straight side may have been very much longer than that shown by the sketch ; a simple look at it is enough to make one believe that this would be the case. But this idea naturally leads us to another digression. Looking again at Fig. 2, we see that acceleration of rota- tion in the nebula would originate where condensation was greatest, that is at the region of greatest density, and have to be propagated from there to its periphery so that it would reach the middle of the cylindrical part sooner than the ends ; and as the nebulous matter at the ends of the cylindrical part could not be abandoned until it had acquired the centrifugal force necessary to overcome gravitation, it would lag behind and overhang, as it were, the middle of the cylindrical part ; which means that instead of continuing to be straight, the line of separation between the nebula and the abandoned matter would come to be concave ; and in this manner the nebula would soon assume the form of a dumb-bell, gradually becoming more and more pronounced as condensation pro- ceeded. One can hardly help concluding that this must have been the way in which the dumb-bell nebula near star 14 Vulpeculae was formed. The representations of it given by Chambers, Vol. III., page 92, Figs. 76 and 77, as seen by Smyth and Sir John Herschel are most confirming of this idea ; not- withstanding the changes of appearance shown by Lord Rosse's reflectors of 3 feet and 6 feet diameter, Figs. 78 and 79, which are not difficult to account for. It is easy to imagine 296 New Theories in Astronomy. how Fig. 78 could be converted into Fig. 79 when observed with a much more powerful telescope. We can conceive the roundest end of it being reduced into the sort of compact segmental form on the left hand side of the figure, and the spread-out part of it into the more diffused segment on the other side ; but the form of the whole figure forces us into another conception. Mr. Chambers says the general outline resembles a chemical retort, but to our eyes it is infinitely more like one half of a dumb-bell broken off from the other. So like it that we feel inclined to ask what has become of the other half. This again makes us think of an enormous dumb- bell nebula dividing itself into two parts, one of which has disappeared or broken up in some manner without leaving any distinguishable traces of its existence, and the other, either forming itself into a double star, assuming in the process the form of a dumb-bell, or actually of one rotating in a direction almost at right angles to that of the original one ; more pro- bably the former of the two. Perhaps we have allowed our ideas, or fancy, to run on too far ; nevertheless, looking over the forms of nebulae represented in Chambers's classical work, and duly considering how inconceivably strange some of them are, there is nothing impossible in all we have said. Returning to the repeated changes of density in the solar planets, we know that the matter first abandoned by the original nebula, through centrifugal force, would be at the lowest stage of density, and that what followed would go on gradually increasing in density as it contracted to the Satur- nian nebula. But, as we have shown that immense quantities of matter belonging, so to speak, to the sun, though actually separated from the original nebula, must have fallen in upon the sheet after being abandoned, it is not difficult to see that the part of the sheet out of which Neptune and Uranus were made, might be more dense than the Saturnian nebula, on account of this matter being added to it ; and that, as the greater portion of it must, at the more advanced stage of the process of condensation, have fallen upon the Uranian part of the ring, because the space from which it fell would be higher, the density of that would be greater than the Neptunian part New Theories in Astronomy. 297 of the sheet ; both of them exceeding the density of the Saturnian nebula. Again, we have supposed, very naturally we think, that all extraneous matter coming in from the equa- torial direction would be intercepted by the rings destined for Neptune and Uranus, so that the density of the ring for Saturn would be only what had been acquired through condensation, and the planet formed out of it would be less dense than those made out of matter accumulated in a different way. It may be argued against this deduction, that density would depend on the degree of contraction, but it is natural to think that lighter would take longer time than heavier matter to condense to the same degree ; besides Saturn is of necessity the youngest of the three planets, and may in due time come to be as dense as either of the other two, but his diameter will decrease proportionately. Coming now to the Jovian nebula, whose diameter we have made to be 1,370,000,000 miles, we have seen, at page 1 1 5, that had it been a perfect sphere by the time it had contracted one thousand miles in diameter, it must have had a flat side of more than 1,400,000 miles in length ? then if we add to that length all that the nebula had inherited from Neptune, Uranus, and Saturn, the cylindrical part of it must have been many millions of miles in length, and the polar very much greater than the equatorial diameter of the nebula. In other words we have to deal with a body having the form of a very long cylinder terminating in spherical caps. To this we have to add that the density of the Jovian was more than in times greater than that of the original nebula. Still farther we have to take into account that the whole of the matter abandoned by that nebula must have been thrown off in less than one-half of the space in which the ring for even Saturn had been abandoned, the breadth of the two rings, as shown by us, see Table III., having been 650,600,000, and 313,400,000 miles respectively. All these things considered, it is clear that the thickness of the ring for Jupiter's system must have been very much greater than what we have given it in the table ; which, coupled with its matter being over six times more dense than that of the preceding ring, is sufficient 298 New Theories in Astronomy. to account for the rise in density, the immense size, and mass of Jupiter. Next, we have the means of accounting for the fact that, the space occupied by the Asteroids is, and has always been, the least dense of any portion of space occupied by the solar system. It is easy to understand that the enormous mass of matter abandoned by the nebula for the formation of the Jovian ring more especially towards the end of the process would have a very appreciable effect, by its attractive power, in helping centrifugal force in freeing matter from the power of gravitation ; the consequence of which would be, that the matter thrown off for the formation of the Asteroidal ring would be considerably less dense than it would otherwise have been. In this way, then, we have the decrease of density, as well as the quantity of matter, in that space very plausibly accounted for. Then, as the nebula continued to contract, the attractive power of Jupiter's ring would decrease proportionally to the square of the distance of the receding mass, ceasing in doing so to lend so great assistance to centrifugal force in the nebula, and so letting it subside into its normal state ; so that the matter abandoned would increase in density in comparison to the space over which it was distributed, thus accounting for the rise in density towards Mars and the Earth. With regard to the fall towards Venus and final rise towards Mercury, we have to take into consideration the anomalies already taken notice of in the dimensions, den- sities, etc. etc., of the two planets Earth and Venus ; it being, we may confidently say, certain that the whole of them have arisen from the same causes. Following up the idea of a dumb-bell nebula as we might have done in the case of Jupiter also as the breadth of space for receiving matter abandoned by the nebula went on rapidly decreasing, the thickness of the ring left behind would go on increasing, and the overhanging matter of the dumb-bell would be deposited always in greater quantity on the outer than the inner part of the ring as it broadened ; we can conceive that the whole extent of the sheet of matter allotted to the Earth and Venus New Theories in Astronomy. 299 would be thicker at the outer than the inner part. Hence, when this part of the sheet came to be divided into two parts for the formation of two planets, the outer would naturally be the greater and denser of the two, and thus occasion the rise in density from Mars to the Earth, and the fall to Venus. Finally the rise in density to Mercury would be only the beginning of the gradual, and final, rise to the sun as it is at present. If the idea of a nebula in the form of a cylinder with hemispherical ends is admitted as possible, or somewhat like a dumb-bell, the extreme diameters of the 9 successive nebulae we have dealt with would be considerably different in their equatorial directions to what we have given them, although their polar diameters might continue to be not far from the same ; but that would have very little effect on the operations we have gone through, seeing we have shown that there could be no actual divisions between them such as we have adopted ; and that the division of the sheet of matter abandoned into separate rings must have been brought about by some means which we cannot explain ; a process, nevertheless, which has been subject to some law, or laws, operating evidently in a regular and steady manner throughout the whole time, during which the matter was being abandoned, as is proved by the general uniformity, or harmony, in the distances of the planets from the sun. Should anyone come to be able to account for the division of this sheet of matter into distinct and separate rings, he will also be able to account for the acceleration of rate of revolution from one planet to another, and for the anomalous rates in the cases of the Earth and Venus. In a former part of our work we have followed up, at different stages, the condensation of the original nebula until it attained the dimensions, appearance, and some of the features of the sun as it is, but we have still something to add as to how the condensation could produce a body so strictly spherical as the sun is represented to be. All the other bodies of the solar system, as far as astronomers have been able to measure them, are spheroids more or less oblate, and it seems strange that the principal should be the only one 300 New Theories in Astronomy. that does not conform to the general figure. It is rather hard on the notion that the original nebula gradually assumed the form of a lens, for it would require a special mode of manipu- lation of a very mechanical kind, rather than the steady, imperceptible self-action of the law of attraction, to transform a lens into even an oblate spheroid ; to transform it into a perfect sphere would be absolutely impossible. For, if at the end of the process it was found that there was too much material to form a sphere, it would be hard to get rid of the superabundance, unless it was converted into meteorites evidently another hand process. On the other hand, should a hole remain to be .filled up, the material would have to be lugged in somehow from some of the errant masses, or lam- beaux, which impact-theorists find it so easy to have at hand when required. Let us then think of why and how it came to pass that the sun is an almost perfect sphere. If we suppose that, when cosmic matter ceased to be thrown off by it, the form of the nebula was that of a cylinder terminating in semi-spherical caps at the ends, it requires no great stretch of imagination to conceive that, between attrac- tion and centrifugal force, the whole mass should be converted through time, first into a prolate spheroid, and then into a perfect sphere. And very possibly time only is required for the sun to become an oblate spheroid, the same as his de- pendent planets. Should this form of nebula not be admissible and we can s