UC-NRLF WALTON AND MABERLY, Price Eighteenpence. ; * : > ::> EDITED BT DIONTSITJS LAEDNEE, D.C.L., Formerly Professor of Natural Philosophy and Aitroaouny in University College, Loudoa. ILLUSTRATED BT ENGRAVINGS ON WOOD. VOL. I. LONDON : WALTON AND MABERLY, UPPER GOWER STREET, AND IVY LANE, PATERNOSTER ROW. 1854. LOAN STACK LONDON : BRADBURY AND EVANS, PRINTERS, WBITEFBIAES. cpi7/ CONTENTS. THE PLANETS : ARE THEY INHABITED WORLDS ? PACK CHAP. I. 1. Aspect of the firmament. 2. Direct evidence on this question not obtained by the telescope. 3. Telescope diminishes distance. 4. Evidence from analogy extremely cogent. 5. Con- sideration of the terrestrial planets. 6. Circumstances which render the earth habitable. 7. Like circumstances to be looked for in the planets. 8. Similarity of position and motion of terrestrial planets. 9. Uniformly supplied with light and heat. 10. Objection of inequality of distance answered. 11. By the effect of atmosphere. 12. Different degrees of light on the planets. 13. Structure of the eye. 14. Its adaptation to different dis- tances. 15. Adaptation of strength of organised creatures to their weight. 16. Adaptation of the rotation of the earth to this organisation . 1 7. Floral clock of Linnaeus. 1 8. Time of rotation not the consequence of a physical law. 19. Rotation of the other planets. 20. Of Mara. 21. Of Yenus and Mercury. 22. Their close analogy to the earth. 23. Inclination of the earth's axis. 24. Produces the seasons. 25. Like provision in the other planets. 26. The atmosphere 1 CHAP. II. 1. Uses of an atmosphere colour of sky. 2. Its effects on temperature. 3. Planetary atmospheres observable. 4. Clouds visible in them. 5. Hence rain, hail, and snow. 6. Winds manifested on the planets. 7. Clouds on Mercury, Venus, and Mars. 8. Continents and oceans. 9. Effect of gravity on planets. 10. Its relation to organised beings. 11. Adaptation of organised beings to the force of gravity 12. Gravity on Mercury, Venus, and Mars. 13. Solar system. Planets. 14. Number of planets groups. 15. Inner group the twenty-five grouped round the sun. 16. The outer group Jupiter, Saturn, Uranus, and Neptune. 17. Their distances from the sun, from each other, and from the earth. 18. Apparent diameters of Sun's disk as seen from these planets Sun's light and heat. 19. Question of habit-ability of these planets considered in reference to sun's light and heat. 20. Great comparative magnitude of CONTENTS. these planets Their volumes Question of habitability con- tinued. 21. Proportionate population, if inhabited. 22. Inves- tigation of physical causes incompatible with their being habitable globes. 23. Application of such causes to Jupiter, and reasoning thereon Necessity of organised world being different from that on the earth. 24. Comparative volume and density of the Earth and Jupiter. 25. Comparison of relative quantities of gravitating matter in Saturn, Uranus, and Neptune, and in the Earth and of density. 26. Comparative weights of bodies placed upon such planets and on the Earth. 27. General results of inquiry as to the habitability of these planets. 28. Atmosphere of these planets. 29. Their diurnal revolution General observations on rotation and their results Position of axis of rotation . .17 CHAP. III. 1. Diurnal rotation of Uranus. 2. Inclination of the axes and limitation of the seasons on the Major planets. 3. Jovian zones and climates. 4. Saturnian. 5. Short days and nights of Major planets. 6. Lightness of their materials. 7. Oceans and seas must consist of a liquid lighter than water. 8. Jovian, Saturnian, and Uranian years. 9. Effects of diurnal rotation on the distribution of clouds. 10. These effects more conspicuous in the Major planets. 11. Manifested by the belts. 12. Telescopic appearance of Jupiter. 13. Herschel and Madler's telescopic views of Jupiter. 14. Jupiter elliptical in form. 15. Discovery of Jupiter's moons. 16. Short months. 17. Lunar eclipses. 18. Telescopic appearance of Jupiter's satel- lites. 19. As seen from Jupiter. 20. The Saturnian system. 21. Atmosphere and moons 33 CHAP. IV. 1. Apparent magnitudes of the moons as seen from Saturn. 2. Their phases Short Saturnian months. 3. Solar and lunar eclipses. 4. Discovery of the rings. 5. Phases of the rings as seen from the earth. 6. Their appearance when seen edgeways in 1848 Schmidt's drawings of them. 7. Mountains upon them. 8. Their dimensions. 9. Discovery of the obscure semi-reflective rings. 10. Dawes' telescopic view of the planet and rings. 11. Appearance of the rings as seen from Saturn. 12. Errors committed on this subject by Bode, Herschel, Madler, and others. 13. Correction of these errors. 14. Appearance of rings will vary with the latitude of the observer. 15. Illus- trative diagrams. 16. Recapitulation. 17. No difficulty can arise in admitting the possibility of differently organised tribes on the different planets. 18. The sun, its physical character incompatible with habitability. 19. The moon not habitable. 20. Nor the satellites. 21. Comets not habitable. 22. The planetoids or asteroids 49 WEATHER PROGNOSTICS. 1. Popular errors as to meteorological phenomena. 2. Weather almanacks, their absurdities Herschel's Weather Table Murphy's Almanack. 3. Influence of the moon on the weather CONTENTS. v PAGE Toaldo's theory Pilgrim's observations Hoi-stay's observations and papers Schiibler's observations and calculations Arago's examination of them Observations of Flau^ergues and Bouvard. 4. Metonic cycle Arago's examination of it, and observations. 5. Arago's examples of the speculation and reasoning of meteorologists. 6. Changes of the moon have no influence on the weather 65 POPULAR FALLACIES. 1. Fallacy of the evidence of the senses. 2. Fallacies of vision. 3. As applied to the sun and moon. 4. Mechanism of the eye its uses. 5. Perceptions of colour 6. Fallacies of smell, taste, and touch. 7. Fallacies as to number 8. Impressions retained by the eye. 9 Fallacies as to distance 10. Fallacies of touch of apparent temperature. 11. Explained by reference to tem- perature of the human body. 12. Cause of apparent coldness of glass and porcelain. 13. Explanations of the feats of moun- tebanks exposing their bodies to a fierce temperature . . .81 LATITUDES AND LONGITUDES. 1. Necessary to know our position on the earth. 2. Poles and equator. 3. Parallel of latitude. 4. Meridian of Greenwich, 5. Latitude and longitude. 6. Methods of determining the latitude. 7. By the sun. 8. By stars. 9. Hadley's sextant. 10. Latitude at sea. 11. To find the longitude. 12. Lunar method. 13. Ball signal at Greenwich . i . . .97 LUNAR INFLUENCES. Popular opinions on Lunar Influences. 2. Red moon. 3. Time for felling timber. 4. Supposed Lunar Influences on vegetables. 5. On the complexion. 6. On putrefaction. 7. On shell-fish. 8. On the marrow of animals. 9. On the weight of the human body. 10. On births. 11. On incubation. 12. On mental derangement and other human maladies Instances of this sup- posed influence during eclipse given by Faber and Ramazzini Amusing anecdote of a village cure near Paris Examples of Yallisnieri and Bacon Observations and examples of Menuret, Hoffmann, Dr. Mead, Pyson, and Dr. Gall. 13. Difiiculty of showing fallacy of these opinions by reasoning or proof Dr. Olbers' partial refutation of them Arago's opinion on them 14. General conclusion that few of these influences have any foundation in fact . 113 vi CONTENTS. METEORIC STONES AND SHOOTING STARS. PAGE (/HAP. I. 1. Necessity of following out the true spirit of the induc- tive philosophy in the investigation of physical phenomena. 2. Circumstances attending appearance of meteorites supplied by past observation Ball-lightning Explosive clouds Chladni's cata- logue of meteoric stones. 3. Remarkable falls of aerolites. 4. Physical condition and analysis of aerolites. 5. Crust of meteor- ites, their internal mass. 6. Their magnitude and velocity. 7. The different hypotheses or theories proposed to explain them. 8. Luminous appearance explained. 9. Hypothesis of Poisson. 10. Atmospheric origin impossible. 11. Volcanic origin inadmis- sible. 12. Lunar origin rejected. 13. Planetary origin generally admitted. 14. Remarkable appearances of shooting-stars re- corded in history. 15. Shower of stars seen in 1788 and 1799. 16. Also in 1822 and 1831. 17. Remarkable shower in 1833. 18. Vast number of shooting- stars seen on that occasion. 19. Their magnitude 129 CHAP. II. 1. Encke's calculation of the direction of the shooting-stars" seen from 1833 to 1838. 2. Apparent magnitudes of those objects. 3. The luminous train which follows them not an optical illusion. 4. Hypotheses to explain them. 5. Heights, directions, and velocity of shooting-stars, calculated by Brandes. 6. A like calculation by Quetelet. 7. A like calculation by Wartmann. 8. Shooting-stars and fire-balls identical. 9. Lunar origin rejected. 10. Received explanation of the phenomena. 11. Difficulties and objections. 12. Description of great shower of stars witnessed in 1799 by Hurnboldt and Bonpland. 13. Description of like showers in 1833-40. 14. August meteors. 15. Halley suggests the use of these meteors to deter- mine the longitude. 16. Table of shooting-stars from 763 to 1837. 17. Inferences from this. 18. Observation of Sir J. Herschel in 1836. 19. Of Wartmann in 1837. 20. Of Tharand in 1832. 21. Annual epochs of the prevalence of these meteors. 22. Why those masses are not visible like the moon and planets by the reflected light of the sun. 23. Zodiacal light. 24. The nebulous matter producing it may cause shooting-stars. 2 5. ^ Shooting-stars may become satellites to the earth. 26. M. Petit claims to have discovered one. 27. Sun-stones. ' . 145 RAILWAY ACCIDENTS. CHAP. I. 1. All travelling attended with danger. 2. Awful disasters incidental to railway travelling. 3. Is railway travelling, how- ever, really more dangerous ? 4. Not practically so considered. 5. The real amount of danger may be calculated. 6. Utility of such a calculation. 7. Imperfections of official reports. 8. Necessary to compare accidents with total amount of travelling. CONTENTS. vi PACK 9. Example illustrating this. 10. Necessary data given in official reports. 11. Reports of 1847-8 and 1850-51. 12. Total mileage of passengers in these intervals. 13. Computation of the risk to life and limb in a journey of given length. 14. Tabular statement. 15. Analysis of its results. 16. Classi- fication of accidents in relation to their causes. 17. The greatest disasters arise from imprudence. 18. Accidents to railway servants. 19. No progress observable in railway safety. 20. Accidents on foreign railways Risk on Belgian lines. 21. Acci- dents on French railways. 22. Contrasted with accidents by stage coaches in and near Paris. 23. Frequent departures, great expedition, and numerous stoppages create danger of collision. 24. Liability to collision with express trains. 25. Accidents by escaping rails. 26. Neglect of points and switches. 27. Analy- tical table of proportion of causes of accidents in 100 cases. 28. Number of brakes. 29. Greater number of brakes necessary with fast trains.- -30. Danger of bringing trains to rest too suddenly. 31. Danger of reversing action of engine. 32. Fog signals. 33. Consequences of collision aggravated by manner of connecting vehicles. 34. Derailment of carriages . . . 161 CHAP. II. 1. Necessity of adopting means of watching trains. 2. Proposals of Great Western. 3. Of the North-Western. 4. Merit of engine-drivers. 5. Example in the accident on the Dee. 6. Investigation of circumstances producing accidents, arising from imprudence or want of vigilance or care. 7. In- stances from reports of railway commissioners. 8. Analysis of 100 accidents produced by imprudence of passengers. 9. Pre- cautions against accidents. 10. Plain rules fo: railway travellers to avoid accidents. 11. Not to get in or out while moving. 12. Not to take an unusual position. 13. Stay in your place. 14. Don't get out on wrong side. 15. Don't cross the line. 16. Avoid going in express trains. 17. Avoid special and ex- cursion trains. 18. In case of accident, get out. 19. Don't attempt to recover a falling article. 20. Take the middle carriage. 21. Don't hand an article into a train in motion. 22. Don't sit in your private carriage. 23. Anecdote of Lady Zetland. 24. Beware of level crossings. 25. Avoid night rail- way travelling 177 LIGHT. Description of eye, and mode in which light is transmitted to it Ways in which objects are rendered visible. 2. Analogy between the eye and the organ of smelling. 3. Analogy between the eye and the ear. 4. Luminiferous ether. 5. Corpuscular theory Undulatory theory. 6. Dndulatory theory explained and examined Roemer's discovery of the velocity of light Newton's solution of the amplitude or breadth of the luminous waves Altitude of luminous waves Table of the magnitudes of the luminous waves of each colour. 7. Consideration of the two theories of light. CONTENTS. PA OB 8. The idea of the undulatory theory entertained by Descartes, Hooke, and others The honour of having reduced the hypothesis to a definite shape attributable to Huygens Dr. Young's mechani- cal reasoning thereon. 9. Malus discovers the polarization of light by reflection The theory greatly extended by Fresnel, Arago, Poisson, Herschel, and others. 10. Relation of light and heat Herschel's discovery apparently establishing the independence of the heating and illuminating effects of the solar rays Berard's experiments. 11. Bodies luminous and non-luminous. 12. Trans- parency and opacity 193 THE GREAT K03SE TELESCOPE. THE PLANETS : ARE THEY INHABITED WORLDS! CHAPTEE I. 1. Aspect of the firmament. 2. Direct evidence on this question not obtained by the telescope. 3. Telescope diminishes distance. 4. Evidence from analogy extremely cogent. 5. Consideration of the terrestrial planets. 6. Circumstances which render the earth habitable. 7. Like circumstances to be looked for in the planets. 8. Similarity of position and motion of terrestrial planets. 9. Uni- formly supplied with light and heat. 10. Objection of inequality of distance answered. 11. By the effect of atmosphere. 12. Different degrees of light on the planets. 13. Structure of the eye. 14. Its adaptation to different distances. 15. Adaptation of strength of MUSEUM, No. 1. 1 THE PLANETS, AKE THEY INHABITED ? organised creatures to their weight. 16. Adaptation of the rotation of the earth to this organisation. 17. Floral clock of Linnaeus. 18. Time of rotation not the consequence of a physical law. 19. Rotation of the other planets. 20. Of Mars. 21. Of Venus and Mercury. 22. Their close analogy to the earth. 23. Inclination of the earth's axis. 24. Produces the seasons. 25. Like provision in the other planets 26. The Atmosphere. 1. WHEN we walk abroad on a clear starlight night, and direct our view to the aspect of the heavens, there are certain reflections which will present themselves to every meditative mind. Are those shining orbs, which in such countless numbers decorate the firmament, peopled with creatures endowed like ourselves with reason to discover, with sense to love, and with imagination to expand to their boundless perfection the attributes of Him of "whose fingers the heavens are the work?" Has He, who "made man lower than the angels to crown him" with the glory of discovering that light in which He has " decked himself as with a garment," also made other creatures with like powers and like destinies, with dominion over the works of His hands, and having all things put in subjection under their feet ? And are those resplendent globes which roll in silent majesty through the measureless abysses of space, the dwellings of such beings ? These are inquiries against which neither the urgency of business nor the allurements of pleasure can block up the avenues of the mind. 2. Those whose information on topics of this nature is most superficial, would be prompted to look immediately for direct evidence on these questions ; and consequently to appeal to the telescope, Such an appeal would, however, be fruitless. Vast as are the powers of that instrument it still falls infinitely short of the ability to give direct evidence on such inquiries. What will a telescope do for us in the examination of any of the heavenly bodies, or indeed of any distant object ? It will accom- plish this, and nothing more ; it will enable us to behold it, as we should see it at a lesser distance. But, strictly speaking, it cannot accomplish even this : for to suppose it did, would be to ascribe to it all the admirable optical perfection of the eye ; for that instrument, however nearly it approaches the organ of vision, is still deficient in some of the qualities which have been conferred upon the eye by its Maker. 3. Let us, however, assume that we resort to the use of a telescope having such a magnifying power, for example, as a thousand : what would such an instrument do for us ? It would in fact place us a thousand times nearer to the object that we are desirous to examine, and thus enable us to see it as we should at 2 EVIDENCE CIRCUMSTANTIAL. that diminished distance without a telescope. Such is the extent of the aid which we should derive from the instrument. Now, let us see what this aid would effect. Take, for example, the case of the moon, the nearest body in the universe to the earth. The distance of that object is about 240,000 miles ; the telescope would then place us at 240 miles from it. Could we at the distance of 240 miles distinctly, or even indistinctly, see a man, a horse, an elephant, or any other natural object ? Could we discern any artificial structure ? Assuredly not ! But take the case of one of the planets. When Mars is nearest to the earth, its distance is about 50,000000 of miles. Such a telescope would place us at a distance of 50,000 miles from it. What object could we expect to see at 50,000 miles' distance ? The planet Venus, when nearest the earth, is at a distance something less than 30,000000 of miles, but at that distance her dark hemisphere is turned towards us ; and when a considerable portion of her enlightened hemisphere is visible, her distance is not less than that of Mars. All the other planets, when nearest to the earth, are at much greater distances. As the stars lie infinitely more remote than the most remote planet, it is needless here to add anything respecting them. 4. It is plain, that the telescope cannot afford any direct evidence on the question whether the planets, like the earth, are inhabited globes. Yet, although science has not given direct answers to these questions, it has supplied a body of circumstantial evidence bearing upon them of an extremely interesting nature. Modern discovery has collected together a mass of facts connected with the position and motions, the physical character and conditions, and the parts played in the solar system by the several globes of which that system is composed, which forms a body of analogies bearing on this inquiry, even more cogent and convincing than the proofs on the strength of which we daily dispose of the property and lives of our fellow-citizens, and hazard our own. 5. We shall first consider this interesting question so far as relates to the group of planets, which from several striking analogies which they bear to our own, have been called the terrestrial planets. These planets, ir number three, and by name Mercury, Venus, and Mars, revolve with the earth around the sun, at distances from that luminary less in a great proportion than the other members of the solar system. We shall next extend the same inquiries to the other bodies composing that system, as well as to those which are distributed through the more distant regions of the universe. 6. In considering the earth as a dwelling-place suited to man and to the creatures which it has pleased his Maker to place in B 2 8 THE PLANETS, ARE THEY INHABITED 5 subjection to him, there is a mutual fitness and adaptation observable among a multitude of arrangements which cannot be traced to, and which indeed obviously cannot arise from, any general mechanical law by which the motions and changes of mere material masses are governed. It is in these conveniences and luxuries with which our dwelling has been so considerately furnished, that we see the beneficent intentions of its Creator more immediately manifested, than by any great physical or mechanical laws, however imposing or important. If having a due knowledge of our natural necessities of our appetites and passions of our susceptibilities of pleasure and pain in fine, of our physical organisation we were for the first time introduced to this glorious earth with its balmy atmosphere its pure and translucent waters the life and beauty of its animal and vege- table kingdoms with its attraction upon the matter of our own bodies just sufficient to give them the requisite stability, and yet not so great as to deprive them of the power of free and rapid motion with its intervals of light and darkness, giving an alternation of labour and rest nicely corresponding with our muscular powers with its grateful succession of seasons and its moderate variations of temperature so justly suited to our organisation : with all this fitness before us, could we hesitate to infer that such a place must have been provided expressly for our habitation ? 7. If, then, the discoveries of science disclose to us in each planet, which, like our own, rolls in regulated periods round the sun, provisions in all respects similar if they are proved to be similarly built, ventilated, warmed, illuminated, and furnished supplied with the same alternations of light and darkness by the same expedient with the same pleasant succession of seasons the same diversity of climates the same agreeable distri- bution of land and water can we doubt that such structures have been provided as the abodes of beings in all respects re- sembling ourselves ? The strong presumption raised by such analogies is converted into a moral certainty, when it is shown from arguments of irresistible force that such bodies are the creation of the same Hand that raised the round world and launched it into space. Such, then, is the nature of the evidence which science offers on this interesting question. Let us endeavour to strip it of such technical forms of language and reasoning as are intelligible only to the scientific, and to present it so as to be easily and agreeably comprehended. 8. If we look at a plan of the solar system, but more especially of that part of it to which we desire now more particularly to call the attention of the reader, the first glance will impress us with 4 ANALOGICAL PROOFS. the idea that the earth is only an individual of a class of worlds of which the three other planets are members. Look at the annexed plan, fig. 1, which represents the relative positions of these planets in their course round the sun. The position of Mercury is represented at M, that of Venus at V, that of the Earth at E, and that of Mars at M'. The circles represent the paths in which they severally move in going round the sun, which is represented radiating its light and heat from the common centre. These four bodies are globular in their form, and not extremely different in their magnitudes. They move round the sun as a common centre in circular orbits, as indicated in the plan, and nearly in the same plane. Now the impression is irresistible that these four globes are 5 THE PLANETS, AKE THEY INHABITED I bodies of the same class ; but let us see the purposes in the eco- nomy of nature which are fulfilled by this common character given to the motion of these planets and the position of the sun. 9. We find, upon considering the qualities of organised bodies, and especially of the species of the animals and vegetables upon the earth, that the maintenance of their physical well-being is essentially dependent on the uniformity and regularity with which they are supplied with the two great physical principles of light and heat. Should these, or either of them, be subject to any extreme variations, such vicissitudes would be incompatible with the organisation of the species. There is a cold on one hand and a heat on the other, under which no organised body could continue to exist, and there are still narrower limits within which it is necessary to confine the temperatures they are exposed to, in order to secure the perfection of their physical health. There are also degrees of light, the intensity of which would be incompatible with the continued perfection of the organs of vision. Seeing then how essential to the well-being of the creatures that people this globe an uniform supply of light and warmth is, we are naturally led to examine the expedient by which this necessary provision has been secured to them. If we had a fire in our neighbourhood which at once supplied light and heat, and that circumstances obliged us continually to shift our position in relation to it, how should we move so as to receive an uniform degree of illumination and warmth from it ? Could we move in any other path than that of a circle around the fire as a centre, keeping thereby always at the same distance from it ? Now this is exactly the path in which the earth moves, as repre- sented in the plan ; and we find that the three other planets severally also move in circles, each keeping continually at the same distance from the common fountain of light and heat.* 10. Since this motion in the case of the earth is an expedient whereby an important end is attained, analogy justifies the conclusion that it is to be regarded likewise as the expedient for the attainment of a similar end in each of the planets. But it will probably be said that the planets are at different distances from the sun : therefore, that although it must be admitted that each planet (considered per se) is supplied uniformly with light * The paths of the planets in moving round the sun when submitted to extremely accurate examination proved to be oval in their form, but their departure from the circular form is so very minute, that if such an orbit were described in its proper proportions on paper, it would be indistin- guishable from a circle. For all the purposes of the argument here advanced, the paths of the planet may, therefore, be taken to be concentric circles with the sun in the common centre. 6 LIGHT AND HEAT, HOW SUPPLIED. and warmth by this circular motion ; yet the intensity of these principles to which they severally are exposed, comparing one with another, is so extremely different as to destroy all analogy between them. 11. In answer to this, we are, however, to consider that the influence of light and heat upon a planet does not depend solely on its distance from the sun. The heat, as is well known, pro- duced by the solar rays, depends on the density of the air which surrounds the objects affected by it. Thus we find the tempe- rature, at great elevations in our own atmosphere, considerably lower than at the mean surface of our globe ; because at these elevations the air becomes so thin as to be incapable of collecting and retaining the sun's heat. We can, therefore, easily imagine, provided the existence of planetary atmospheres be conceded, that their densities have been so regulated, that the nearest planets to the sun, which receive the greatest intensity of its rays, may not, after all, be subject to a greater temperature than the most remote ones, which are exposed to the least intensity of its rays : just as we find that the temperature of the summits of lofty mountains at the tropics is as low as the temperature of some of the polar latitudes. It is plain, then, how the effects of the various distances of the planet from the sun may be equalised and compensated. The means of accomplishing this are provided in the form of atmospheres, as we shall presently see. 12. But let us turn to the consideration of the solar light. The intensity of the sun's light varies with his distance exactly in the same proportion as that of his heat ; and the brightness of the day in each of the planets would be in the exact proportion of the apparent magnitudes of the sun as seen from them severally. Now, it is evident, that as we approach any object, its visual magnitude increases, and, as we recede from it, its visual magnitude diminishes. A balloon seen at the place from which it makes its ascent appears of vast dimensions. Seen at a great height in the air, it is diminished to a mere spot. Looking from the summit of the cliffs of Dover, Edgar says to Kent Half way down Hangs one that gathers samphire ; dreadful trade ! Methinks, he seems no bigger than his head: The fishermen, that walk upon the beach, Appear like mice ; and yon' tall anchoring bark, Diminish'd to her cock ; her cock, a buoy Almost too small for sight. Knowing the relative distances of Mercury, Venus, the Earth, and Mars from the sun, nothing is more easy than to ascertain by calculation the relative apparent magnitudes of the sun, as 7 THE PLANETS, AKE THEY INHABITED Fig. seen from them severally; since the apparent diameter must decrease in exactly the same proportion as the distance from the sun increases, and vice versa. In this way we find that the sun, as seen from the four planets, has the relative magni- tudes shown in fig. 2, where E being taken to represent the disc of the sun, as seen from the Earth, M will be its disc as seen from Mercury, V, as seen from Venus, and M', as seen from Mars. The brightness of the sun's light at Mercury will be greater than at the Earth, in the same proportion, as M is greater than E, and its light at Mars will be less bright than at the Earth, in the same ratio as that in which M' is less than E. It might, there- fore, be concluded that the light at Mars would be too feeble, and the light at Mercury too intense for vision. 13. A slight consideration of the structure and functions of the eye will, however, demonstrate how easily such difficulties may be removed. The perception of light which any creature possessing that organ acquires, depends (cceteris paribus) upon the mag- nitude of the circular aperture or foramen, in front of the eye, called the pupil, which has, externally, the appearance of a circular black spot ; but which is, in reality, a cir- cular hole through which the light is admitted to the interior of the chamber of vision, there to affect the membranous coating which transmits its influence to the brain and causes the sensation. This will be better understood by refer- ence to the annexed figures, 3 and 4, the former representing the external form and appearance of the eye, and the latter a section of the eye-ball, made in a horizontal plane through the dotted line A B. The line P (fig. 3), points to the pupil, I to the iris, a coloured ring surrounding the pupil ; and W to the white of the eye. In fig. 4, P points to the pupil, I to the iris, and N and to a membranous coat full of nerves and blood-vessels which lines the inside of the eye-ball. The light, entering from M G through the pupil, and passing through the internal humours of the eye, which are perfectly transparent, strikes on that membranous coating and acts upon it in such a manner as to produce a perception. The apparent brightness of the light will obviously 8 STRUCTURE OF THE EYE. depend on the quantity which enters the eye through the pnpil, and the sensitiveness of the membranous coating on which it acts. Fig. 3. i 4 \\ Fig. 4. 14. If, then, the pupils of eyes on Yenns or Mercury were smaller, and those on Mars larger, in the same proportion as E is smaller than Y and M (fig. 2), and larger than M', the mem- branous coating having the same sensibility, the apparent brightness of the solar light would be the same to all of them. Or supposing the pupils of the eyes to have the same magnitude, a like effect would be produced by imparting to the membranous coatings different degrees of sensibility, the sensibility on Yenus and Mercury being less, and on Mars greater, than those of the eyes upon the Earth. 15. In considering the powers of locomotion and strength con- ferred upon animals on the earth, we find that they have certain limitations ; that animals are capable of exercising these powers for certain periods, varying, it is true, among individuals, but still in the main comprised within certain narrow limits. We find that after the lapse of certain intervals, bodily repose is wanted. But besides the disposition to activity and locomotion and the alternate want of rest, animals in general have also THE PLANETS, ARE THEY INHABITED? other wants and capabilities of enjoyment which are periodical. Thus they a,re capable of wakefulness for certain periods, after which recurs the physical want of sleep. Now upon a general survey of the creation, it is found that the average period which must regulate the intervals of labour and rest, of wakefulness and sleep, corresponds in the main with that which regulates the alternations of light and darkness. In the vegetable kingdom we find prevailing also periodical functions, certainly not so obvious and apparent, but not on that account the less interesting, which are ascertained to have the same close alliance with the period that regulates the returns of light and darkness. Plants undergo certain changes and suffer certain effects, in the presence of solar light, which are different from, and in some respects contrary to, those which they undergo in its absen-ce. These changes are essential to the vegetable health of the creature ; without them the tribes of plants would be extinct. 16. The duration of these operations is just as essential as their alternations. Light must be present a certain time, and neither more nor less ; and its absence must be equally regulated by limits, otherwise the plant must perish. There is, then, it is evident, an essential relation between the functions and qualities of the vegetable kingdom between the power of activity, the susceptibility of enjoyment and the physical wants of animals, and the periods which separate light from darkness ; but what* are those periods ? What is the mechanical expedient to which He has resorted to accomplish His inscrutable purposes, who divided the light from the darkness, and "saw that it was good" 1 Nothing can be more simple. Nothing can be more beautiful. Nothing can be more admirably perfect. While the globe of the earth makes its annual course round the sun, it has at the same time a spinning motion, on a certain diameter, as an axis, in virtue of which it successively exposes all parts of its surf ice to the light and warmth of the sun. Bach complete rotation, is accomplished in the interval which we call twenty-four hours. All points on our earth are alternately exposed to and with- drawn from the solar light. The earth, in its annual movement round the sun, is represented in Fig. 5. It will be seen that one hemisphere is shone upon by the sun while the other is dark. But as the globe revolves on its axis once in twenty-four hours, each side is successively exposed to the sun's light and heat, for average intervals of twelve hours. The culinary process of turning meat by a string or on a spit, successively exposing every side to the heat of the fire, is a homely illustration of this expedient. 10 DAYS AND NIGHTS. Now when we reflect on the correspondence between these intervals and the indispensable wants of all organised creatures, can we for a moment doubt that the earth was made to turn upon its axis in that particular time rather than any other, because it was more conducive than otherwise to the well-being of the countless myriads of species, the production of the Divine hand, for whose enjoyment the earth was made ? Had the time of rotation been materially less than it is, our periods of activity and labour would be too short to prepare us for the return of darkness, and had the time, of rotation been greater, we should have needed rest before the return of the natural epoch designed for it. As it is, the natural vicissitudes are nicely adapted to our wants; and yet our organisation is in no way connected physically with the rotation of the earth, by any relation of the nature of cause and effect, and to suppose such an adaptation fortuitous, would be an outrage upon all principles of probability. This mutual fitness is, then, another of the many proofs which offer themselves that the earth as a dwelling, and man as a dweller, have been expressly designed each for the other. 17. Many examples may be given of this correspondence between the time of rotation of the earth upon its axis and the periodical functions of the organised world. Linnaeus proposed the use of what he termed a floral clock, which was to consist of plants which opened and closed their blossoms at particular hours of the day. Thus, the day-lily opens at five in the morning, the common dandelion at six, the hawk-weed at seven, the marigold at nine, and so on ; the closing of the blossoms marking 11 THE PLANETS, ARE THEY INHABITED I corresponding hours in the afternoon. Nor can this be regarded as a specific effect of light upon the plants, for when the flowers are introduced into a dark chamber they are found to open and close their blossoms at the same times. 18. The necessity of maintaining a correspondence between the intervals of activity and repose, the taking of food, &c., and the period of light and darkness, was shown in the case of voyages made to the north pole, where navigators attained those latitudes in which the sun never rises for several weeks, in which cases it was found necessary to make the crews of the ships adhere to the habit of retiring at nine o'clock and rising at a quarter before six. Under these circumstances they enjoyed a state of salubrity very remarkable, notwithstanding the trying severity of climate to which they were exposed. As an example of creative beneficence the rotation of the earth in twenty-four hours would lose none of its force if that par- ticular period, like the time of its revolution round the sun, were a necessary consequence of an established physical law. It is interesting, nevertheless, to observe that such is not the case. No law of matter would have prevented the earth from receiving any other rate of rotation more or less rapid. It might have made a single rotation a year, in which case the average alternations of day and night would have been six months, or it might have made a single rotation in an hour, in which case the alternations would have been thirty minutes. Such conditions though physically admissible, would be obviously incompatible with the continuance of the organised world. We are, then, to regard this period of diurnal rotation of the earth and its admirable adaptation to the wants and well-being of the creatures which inhabit it, not as the result of any law of physics, but as a provision directly emanating from divine beneficence, and as an example of the infinite k skill of the hand which at the moment of its creation launched the earth into space. 19. Seeing then, that the expedient of making the globe of the earth turn upon its axis in twenty-four hours is one productive of such multifarious benefits, and so intimately related to the organised species of our globe, that were it to turn otherwise than it does, in a greater or less time, an entire derangement of the animal or vegetable economy would ensue, it becomes an interesting question to ascertain whether the other planets are provided with a similar expedient ; and if so, to what extent the application of such expedient corresponds with the case of the earth. We accordingly find that all the planets without exception have a motion of rotation on certain diameters as 12 COXTIXEXTS AND SEAS. an axis, while they make their periodical revolutions round the sun, and that the diameter in which they so rotate has been selected in such a manner as to secure to each of them regular alternations of light and darkness in every part of their surfaces ; in fact, they, like the earth, have days and nights. But are those days and nights regulated by the same intervals as ours ? for that is an important question ; such intervals being as we have shown, a key to the organisations and functions of the creatures upon them respectively. 20. When a telescope of ade- quate power is directed to the planet Mars, it is observed that the surface of his disc is diversi- fied by certain features of light and shade like that of the moon. Some of these lights and shadows are shifting and variable, but most of them are permanent and unalterable. In fig. 6, a view of these permanent lineaments as they are presented in a certain aspect is given, taken from a telescopic drawing of the planet, made by M. Madler, the celebrated Prussian observer. Now if these outlines of light and shade be watched for some hours, they will be observed to be carried slowly from one side of the disc to the other. Each of these will in succession dis- appear at one side, others coming into view at the other, and after an interval of about twelve hours, the marks which disap- peared at one side will be found to re-appear at the other, and this goes on continually. It is scarcely necessary to say that those are the effects of the rotation of the planet on its axis, and since the same features after disappearing at one side always return to the same precise position on the disc after an interval of 24h. 37m. 22s., it follows that the planet turns upon its axis in that interval. 21. By means very nearly similar strong reasons have been found for concluding that the globe of Venus turns on its axis in 23h. 21m. 21s., and that of Mercury in 24h. 5m. 22. Thus it appears that these three planets, not only have days and nights, but that these days and nights are for all practical purposes similar to those of the Earth. They are regulated by the same average duration ; and He that gave them those alter- nations has seen it good to " divide the light from the darkness " after the same fashion. 13 THE PLANETS, ARE THEY INHABITED ? If, then, the duration of our days and nights be evidently regulated with a view to the accommodation and well-being of the organised creatures to which the earth has been appropriated, we are surely warranted by all analogy in concluding that the adaptation of the same expedients in the planets Mercury, Venus, and Mars, has been directed to the same beneficent purposes, and that the creatures upon them, as upon the earth, are so organised as to require the same intervals of labour and rest, of activity and repose, of wakefumess and sleep. 23. In considering the expedient by which days and nights are secured to the planets, it is interesting to contemplate the parti- cular position of the diameters on which they have been made to turn. There are a great variety of different diameters upon which the earth might have spun while it revolves round the sun. It might, for example, have turned on a diameter at right angles to its annual orbit. If such had been the case we should have had equal days and nights throughout the entire year, and at every part of the earth. If its axis, as it might have been, had been in the plane of its annual orbit, the sun would have been constantly above the horizon for an interval of several weeks in summer, and con- stantly below it for a like interval in winter. The duration of these intervals of incessant light and incessant darkness would have varied in different parts of the earth, increasing with the latitude. No diurnal alternations of light and darkness would take place except for a short interval before and after the equinoxes. It is not necessary to enlarge upon the consequences of such an arrangement, to render it apparent that they would be utterly incompatible with the well-being, and perhaps even with the maintenance, of the organised world. In the first of the cases here supposed, we should have been deprived of the seasons sind of the means of maintaining a con- venient chronology, and in both cases we should be stripped of many of the benefits and utilities arising from the present arrangement. k But, between these extreme possible positions of the axis of rotation, there are a,n infinite variety which would have been nearly as unsuitable. Had the axis leaned down nearly to the ecliptic, consequences would have ensued almost as fatal as those which a position in the plane of the ecliptic would have inferred. We find, however, in fact, that a position has been given to this axis slightly inclined from the perpendicular, as represented in fig. 5. In virtue of this inclination the northern hemisphere leans toward the sun during one half of the year, and 14 PLANETARY SEASONS. the southern hemisphere during the other. "We enjoy by this expedient the grateful succession of seasons ; it is thus that spring, summer, autumn, and winter, follow each other with pleasant variety, marking in their progress by obvious phenomena the course of time. Yet this inclination or stooping of the axis is so regulated that the extremes of the seasons are confined within such moderate limits as are necessary and conducive to the physical well-being of the numerous tribes which people the earth. It is true that this succession of seasons was not indispensably necessary to the continuance of the races that inhabit the earth, for had the axis been perpendicular to the orbit so as to render days and nights perpetually an/1 everywhere equal, the organised world would still have continued to exist though subject to certain modifications. 25. Xow, on observing the position of the axis on which Mars revolves, we find that it is inclined to the plane of the orbit of that planet, at an angle of 28 27', not very different from that at which the axis of the Earth is inclined to the ecliptic. The seasons and climates of Mars are therefore similar to those of the Earth. Observation has not yet determined the position of the axes of rotation of Venus and Mercury, but it is probably not materially different from that of Mars and the Earth. Thus we see that not only the same alternations of light and darkness birt the same succession of seasons, regulated by nearly the same limits of temperature, the same diversity of climates, separated by nearly the same limits of latitude which prevail on Earth, have also been ordained for those three planets. 26. The atmosphere which surrounds the earth is an appendage which has an obvious and important relation to the animal and vegetable kingdoms. That respiratory beings depend on it for the maintenance of their vitality is obvious. The mechanical and chemical functions of the breathing organs is expressly adapted to it. Its relation to vegetable life is not less important. But besides these qualities, without which life would become extinct on the surface of the globe, the atmosphere administers to our convenience and pleasures in other ways. It is the medium by which sound is transmitted ; and as the apparatus of the lungs is adapted to operate chemically upon it, so as to impart to the blood the principle by which that fluid sustains life, so the exquisite mechanism of the ear is constituted to receive the effects of its pulsations and convey them to the sensorium to produce the perception of sound. Again, the mechanism of the organs of voice is adapted to impress on the atmosphere those 15 THE PLANETS, ARE THEY INHABITED 1 pulsations, and thereby to convey its intonations to the corres- pondingly susceptible organisation of the ear. Without the atmosphere, therefore, even supposing we could live in its absence, however perfect might be our organs of speech and hearing, we should possess them in vain. Voice we might have, but no word could we utter ; listeners we might be, but no sound could we hear ; endowed with the full powers of hearing and speaking, we should nevertheless be deaf and dumb. 'Another important manner in which the atmosphere adminis- ters to our convenience is, by diffusing in an agreeable manner the solar light, and mitigating its intensity. In this respect, the atmosphere may be considered as performing in regard to the sun what the imperfect transparency of a ground-glass shade performs for the glare of the lamp. In the absence of an atmosphere, the light of the sun would only illuminate objects on which its direct rays would fall ; we should have no other degrees of light but the glare of intense sunshine, or the most im- penetrable darkness. Shade, there would be none ; the apartment whose casement did not face the sun, at the mid-day would be as at midnight. The presence of a mass of air extending from the surface of the earth upward to a height of more than forty miles, becomes strongly illuminated by the sun. This air reflects the solar light on every object exposed to it, and as it spreads over every part of the earth's surface, it conveys with it the reflected, but greatly mitigated light of the sun. ' When the evening sun withdraws its light, the atmosphere continuing to be illuminated by its beams, supplies the gradual declining twilight which terminates in the shade of night. Before it rises, in like manner, the atmosphere is the herald of its coming, and prepares us for its splendour by the grey dawn and increasing intensity of morning twilight. In the absence of an atmosphere, the moment of sunset would be marked by an abrupt and instantaneous transition from the blaze of solar light to the most impenetrable darkness ; and for the same reason, the morning would be characterised by an equally abrupt change from absolute darkness to broad, unmitigated sunshine. 16 MARS. SKETCH OF THE OUTLINES OF CONTINENTS AND OCEANS, AND THE SNOW RKOION OF THE POLAR CIRCLE OX THS .-OUTHERX HEMISPHERE OF TUK PLANET MARo, THE OBSERVATIONS OK MADLKR. THE PLANETS; AKE THEY INHABITED WORLDS? CHAPTER II. 1. Uses of an atmosphere colour of sky. 2. Its effects on temperature. 3. Planetary atmospheres observable. 4. Clouds visible iu them. 5. Hence rain, hail, and snow. 6. Winds manifested on the planets. 7. Clouds on Mercury, Venus, and Mars. 8. Continents and oceans. 9. Effect of gravity on planets. 10. Its relation to organised beings. 11. Adaptation of organised beings to the force of gravity 12. Gravity on Mercury, Venus, and Mars. 13. Solar system Planets. 14. Number of planets groups. 15. Inner group the twenty-five grouped round the sun. 16. The outer group Jupiter, Saturu, Uranus, and Neptune. 17. Their distances from the suu, from each other, and from the earth. 18. Apparent diameters of Sun's disk as seen from these planets Sun's light and heat. MUSEUM No. 3. o 17 THE PLANETS, ARE THEY INHABITED"? 19. .Question of habitability of these planets considered. in. reference to suu's light. and heat. 20. Great comparative magnitude of these planets Their volumes Question of habitability continued. 21. Proportionate population, if inhabited. 22. Investigation of physical causes incompatible with their being habitable globes. 23. Application, of such causes to Jupiter, and reasoning thereon Necessity of organised world being different from that on the earth. 24. Comparative volume and density of the Earth and Jupiter. 25. Comparison of relative quantities of gravitating matter in Saturn, Uranus, and Neptune, and in the Earth and of density. 26. Comparative weights of bodies placed upon such planets and on the Earth. 27. General results of inquiry as to the habitability of these planets. 28. Atmosphere of these planets. 29. Their diurnal revolution General observations on rotation and their results Position of axis of rotation. 1. IN the absence of an atmosphere we could have no. clouds ; day would be one unvaried wearisome glare of the sun. The bright azure sky, so grateful to the sight, is nothing more than the natural colour of the air reflected to the eye. The air which fills a room is not perceived to be blue only because it is not present in sufficient quantity to excite in the eye any perception of its colour ; just as a glass of sea- water seems translucent and colourless, while the same water viewed through a consider- able depth, appears with its proper hue of green. When we look up, therefore, through forty miles of air, we behold that fluid of its proper tint of blue. In the absence of the atmosphere the great vault of the heavens would present one unvaried and eternal black, the stars dimly twinkling here .and there, the whole forming a most funereal contrast with the bright orb which would be seen holding its solitary course through this eternal expanse of darkness. 2. The atmosphere produces effects on the temperature of our habitation which are not less important. It retains and diffuses warmth, whether proceeding from the sun above, or from sources of internal heat within the globe itself. What situation with respect to temperature we should be placed in by its absence, or even by a considerable diminution of its quantity or density, may be easily inferred by considering the state of those parts of the earth which are placed at such an altitude as to leave below them a large portion of the atmosphere. The summits of lofty ridges, such as those of the Alps, the Andes, and the Himalayan, are examples of this. No intensity of direct solar heat can com- pensate for the absence of a sufliciently dense atmosphere, and even within the tropics, water cannot exist in a liquid form at elevations above 14,000 feet. The summits of the Andes are clothed in everlasting snow. Had we, therefore, been unprovided with an atmosphere, or USES OF AN ATMOSPHERE. even had our atmosphere been so rare and attenuated as it is at an elevation of three miles (scarcely one-tenth of its whole height), the waters of our oceans would have been solid. Vege- tation could never have existed, and in spite of the light and genial warmth of the sun in spite of the grateful changes of season in spite of the beautiful and simple provision by which, spring succeeds winter, and is followed by summer and autumn, the earth would have been a barren and arid waste, enve- loped in a shell of eternal ice, devoid of life, motion, form, and beauty. Seeing, then, how necessary to the existence of an animal and vegetable world an atmosphere is how indispensable its presence is to a society of creatures whose means of intercommunication is sound and yet bearing in mind at the same time that this atmosphere is not essential to any of the great mechanical functions of the earth in the economy of the solar system considering also that without its presence the part which that earth, as a whole, performs in the society of the planets, would be the same as it now is can we come to any other conclusion than that this atmosphere was cast around the earth expressly with a view to the well-being of its occupants to afford them a genial warmth to give them diffused and gentle light to convey the varieties of sound to promote and facilitate social felicity, by supplying the means of intercommunication by- language to preserve the seas liquid and supplying propitious winds to stimulate the intercourse of nations and knit together the races of beings who occupy its most distant points by the kindly bonds of reciprocal beneficence] If then such be ad- mitted to be some among the many of the purposes and uses of our atmosphere, the question whether other planets, in situations resembling ours, are occupied by similar beings,, must be materially influenced by the result of an investi- gation as to whether or not these planets are supplied with like atmospheres. 3. Telescopic observations have most clearly and satisfactorily answered this question. The atmospheres around the planets are as palpable to sight as the clouds which float on our own. Yenus and Mercury are enveloped in thick atmospheres : in the former the air is especially conspicuous, nay, we can even see the morning and evening twilight in that distant world. The atmosphere of Mars is likewise apparent. We see the clouds floating on it. 4. The ascertained existence of clouds in the planets proves more than the mere presence of atmospheres upon them. An atmosphere is necessary to support clouds, but must not be c2 19 THE PLANETS, ARE THEY INHABITED ? identified with them. Clouds are DO more parts of the atmo- sphere than the mud and sand which float in a turbid river are parts of its waters. Water is converted into vapour by the agency of the sun and wind. This vapour, when it escapt-s from the surface of the liquid, is generally lighter, bulk for bulk, than that part of the atmosphere contiguous to it. It rises into more exalted regions, where, by the agency of cold, and by electricity, it is made to resume its liquid state, but in such minute particles that it floats and forms those semi-opaque masses called clouds. Clouds are, then, in fact, water existing in a very minute state of mechanical division, and affected iu peculiar ways by electricity. 5. When these particles are caused to coalesce into drops or spherules of water an effect which may arise from temperature or electricity, or both combined their weight renders their further suspension impossible, and they descend to the surface In the form of rain : or if the cold be so great as to congeal the particles before they coalesce into globules, they descend in the 'form of snow ; or, finally, if by the sudden evolution of heat caused by electrical influences their solidification is eifected in drops, they come down in the form of hail. Thus wherever the existence of clouds is made manifest, there WATER must exist ; there EVAPORATION must go on ; there ELEC- TRICITY, with its train of kindred phenomena, must reign ; there IJAINS must fall ; there HAIL and SNOW must descend. 6. That healthful and refreshing winds agitate the atmospheres of the group of worlds in the centre of which our sun presides, and of which it is the common bond that showers refresh their surfaces that their climates and seasons are modified by evapo- ration that their continents are bounded by seas and oceans that intercourse is facilitated by winds which convert the surfaces of their waters into highroads for nations these and a thousand other consequences of what has been here explained, all tending to one conclusion that these various globes are placed in the 'System for the same purpose as the earth that they are in fact, the dwellings of beings in all respects, even from their lowest physical wants to their highest social advantages, like ourselves, crowd upon the mind so thickly that we can scarcely give them expression in a clear and intelligible order. It may be asked whether by immediate observation we may not perceive the geographical surfaces of the planets, so as to declare by direct survey their divisions of land and water, mountain and valley, and other varieties of surface. Even the most superficial view of the subject will render apparent some great difficulties which mtibt obstruct such an 20 PLANETARY GRAVITY. inquiry with respect to most of the planets. The very presence of those atmospheres and the clouds with which they are loaded, offers a serious obstruction to any observations having for their object to ascertain the geographical character of their surfaces. The great distance of some of them is a formidable obstacle to such an inquiry ; still, where some peculiar circum- stances favour the observation, something has been done in this investigation. 7. Venus and Mars, the two planets in the system which come nearest to the path of the Earth, are evidently the most eligible objects for such an inquiry, and sufficient has been ascertained, especially with regard to the latter planet, to draw very closely indeed the ties of analogy by which the planets are associated with the earth. 8. The existence of continents and oceans, and even the configu- ration of their outlines has been clearly traced on Mars. The ?now which covers his polar regions during the winter, has been distinctly seen, and has even been observed partially to dissolve and disappear under the influence of the summer heat. The clouds with which Venus and Mercury are so constantly enve- loped, combined with other obstructions peculiar to the positions of these planets, have rendered like observations respecting them impracticable. It has, nevertheless, been ascertained that their surface, like that of the Earth, is marked by mountain-chains of great elevation. 9. In tracing the analogies which prove the suitableness of tho- planets for habitable globes, and which connect them by ties ot kindred with the earth, one of the most important and interest- ing is dependent upon the quantity of matter composing these- planets, compared with their volumes or bulks. Let us see how this affects the condition of the organised creatures that dwell upon them. 10. All organised beings, whether animal or vegetable, are endowed with a certain limited amount of bodily strength. In the case of animals, which have powers of locomotion, this strength is regulated with reference to their weight, and the extent and quantity of motion necessary for their well-being on the surface of the globe. The structure of every animal is such, in the first place, as to give it strength to support and move its own body ; but this is not enough ; it must have a further amount of disposable force to enable it to supply its own wants by the pursuit of its prey; by the collection of its food ; by the erection of its dwelling ; and, in general, by its labour in the supply of its physical wan'?. In the case of vegetables, the strength must be sufficient to support its weight, and resist those external 21 THE PLANETS, ARE THEY INHABITED ? disturbances to which it is exposed such as the action of winds and other natural effects. But what, let us ask, regulates this necessary quantity of strength ? What is the chief resistance which it has to overcome ? We answer, mainly the weight of the creature itself. But again ; what is this weight? It is a force produced by what 1 By the combined attractions of the whole mass of matter composing the globe of the earth, exercised upon the matter composing the creature itself ; thus the weight of a man is merely the amount of the attraction of the globe of the earth exercised upon the matter composing the body of the man. The amount of this attraction, therefore, depends upon the quantity of matter in the earth ; but not on that alone ; it is a universal law of nature, that the energy of the attraction exerted by matter, is increased with the proximity of the attracted body to the centre of the attracted mass. Now, if the matter composing the globe of the earth were condensed into half its present bulk, all bodies placed upon the surface, being propor- tionally nearer the centre, would be attracted with greater energy ; and, on the other hand, if the matter of the earth were swelled into a larger bulk, the distance of objects on the surface from the centre being proportionally increased, the energy of the attraction would be diminished. In the one case the weights of all bodies would be augmented, and in the other they would be diminished. The weights, then, of bodies placed on the surface of the earth depend conjointly on the mass of matter composing the earth, and on its density. 11. It is evident then, that the adaptation which we see usually to prevail between the strength of animals and plants and their weights, is, in reality, an exquisite harmony which is maintained between the strength of these infinitely various tribes of organised creatures, and the mass and density of the globe upon which they are placed ; the slightest disturbance or change in this relation would utterly derange the fitness of things, and would render the globe and its occupants, whether animal or vegetable, unsuited to each other. The amount of attraction, or, to use the more familiar term, the weight of the body on the surface of the globe is, then, an index, so to speak, to the organisation of the creatures placed upon the globe. If we would, then, inquire respecting the probable organisation of the dwellers upon the planets, one of the means of our inquiry would be to ascertain what would be the weights of bodies upon their surfaces. Physical science enables us perfectly to accomplish this The jnasses of matter composing all the planets have been d'scovered with a great degree of precision. Their magnitude have also been measured. Now, to ascertain the weights of budies placed upon 22 SOLAR SYSTEM. the surface of any of them, it is only necessary to consider their masses and their magnitudes. The weight of a body placed upon any planet is greater or less, cceteris paribus, than the weight of a body placed upon the earth, just in proportion as4he mass of matter in the planet is greater or less than the mass of matter in the earth. If the distance from the surface to the centre of the planet be double the corresponding distance in the case of the earth, then the weight of bodies upon its -surface would, on that account alone, be four times less than' in the case of the earth. But if, at the same time, the mass of matter in the planet were sixteen times greater than the mass of matter in the earth, then the weight of bodies on the planet, on that account alone, would be sixteen times greater. The weight, then, on. the one score, would be sixteen times greater, and on the other, four times less ; the result being that the actual weight under such circumstances would be four times greater than upon the earth. Such are the principles by which may be calculated the weights of bodies upon the surfaces of the different planets. 12. It has been found that the weights of bodies on the surface of Venus are nearly the same as on the Earth, but that on Mercury and Mars the weights of bodies are only half of those which they would have if placed on the Earth. The inference obviously is, that organised beings on Venus would require to be endowed with the same bodily strength exactly as upon the Earth, but that half the strength would suffice on Mars and Mercury. The numerous analogies which we have indicated give the highest degree of probability, not to say moral certainty, to the conclusion that the three planets, Mars, Venus, and Mer- cury, which, with the Earth, revolve nearest to the sun, are like the Earth appropriated by the Omnipotent Creator and Ruler of the Universe to races very closely resembling, if not absolutely identical with, those by which the Earth is peopled. 13. The solar system consists of the sun, a globe of stupendous magnitude, maintaining a position, relatively fixed in the centre, and thirty- three planets revolving round it in paths which do not differ sensibly from, concentric circles. 14. These thirty-three planets are characterised by very striking differences in relative position and in magnitude, and have in relation to these differences been classed in three groups. 15. The inner group consists of four: Mercury, Venus, the Earth, and Mars. They are all included within a circle ot 150,000000 of miles radius described round the sun as a centre, the distance of the earth being nearly 100,000000 of miles. The circumstances attending these globes,- their mutual analogies, and the probability, if not the moral certainty, that 23 THE PLACETS, ARE THEY INHABITED ? Fig. I. they are tlie habitations of organised tribes- similar to those which inhabit the earth having been very fully explained, we. propose now to explain the circumstances, which attend another of these groups. The manner in which the thirty-three planets are distributed around the sun is represented in fig. 1. The relative distances- are there represented as nearly as is practi- cable on their real scale. Twenty-five of the entire number of planets are crowded together at a distance from the sun about two-and-a-half times greater than that of the earth. These constitute a group apart,, characterised by some very curious cir- cumstances, which we shall explain here- after. 16. The four outer planets, Jupiter, Saturn, Uranus, and Neptune, form the other group which we now propose to examine. 17. The relative distances of these bodies from the sun, from each other, and from the earth, are exhibited in the diagram (fig. l) r where the fifth part of an inch represents, one hundred millions of miles. The dis- tance of Jupiter from the sun on the plan being an inch, its real distance is, m round numbers, five hundred millions of miles. That of Saturn being l^g inch, that of Uranus 3 5 6 5 inches, and that of Neptune- 5^ inches ; the actual distances of these. three planets are 900, 1,800, and 2,800 millions of miles respectively, all the dis- tances being, as before expressed, in round numbers. 18. When it is considered that the appa- rent magnitude of the sun and the- intensity of its light and heat decrease in- a very high proportion as its distance is augmented, it will be evident that that body, considered as the means of illumi- nation and warmth, must minister to- these several globes extremely different quantities of those necessary physical 24 SOLAR LIGHT AT PLANETS. principles. It has been already stated that the apparent diameter of the sun's disk is less in exactly the same proportion as the. distance of the observer from that luminary is greater. Since, therefore, the distances of Jupiter, Saturn, Uranus, and Neptune are severally five, nine, eighteen, and twenty-eight times the earth's distance, the apparent diameters of the sun's disk, as seen from them, will be |, , ^ and of its diameter, as seen from the earth. Fig. 2. Fig. 3. If the white circle E (fig. 2) be imagined to represent tbe apparent disk of the sun, as it is seen by an inhabitant of the earth, then J (fig. 3) will represent its appearance to an inha- bitant of Jupiter, s its appearance to an inhabitant of Saturn, u to an inhabitant of Uramis,and N to an inhabitant of Neptune. The light and heat which it would supply to each of these planets would be in the exact proportion of the apparent surface of the solar disk, and since the areas of circles are as the squares of their diameters, it would follow that the solar light and heat at Jupiter is 25 times, at Saturn 81 times, at Uranus 324 times, and at Neptune 784 times less than at the earth.* 19. In considering the question of the habitability of these globes, it might appear from these numbers that the illuminating and heating power of the sun would be so diminished by distance as to be incompatible with the existence of organised races, at least on the more distant of those planets. It must, however, be considered that the illuminating power of the sun would be the same as at the earth, if only the pupils of the eyes were enlarged in the same ratio as the apparent superficial magnitude of the * These numbers are not the exact ratios, but are near enough for the present illustration. For more precise results see "Handbook of Natural Philosophy and Astronomy" (2,994). 25 THE PLANETS, ARE THEY" INHABITED ? Fig. 4. sun's disk is diminished, or that the same effect would be pro- duced by a proportionally increased sensibility of the retina. In like manner the diminished calorific power of the sun's rays proceeding from their dimi nished density, might be compen- sated by modified atmospheric con- ditious, just as we find with the same density of the solar rays all climates in ascending on tropical mountains to various altitudes from the level of the sea to the line of perpetual snow. These points have been already so fully developed and explained, that we need not here further insist upon them. It is apparent, therefore, that so far as the vastness of their distances from the sun compared with that of the earth affects the illumination and warmth supplied to them, there are no grounds for concluding that they may not be the habitations of races organised in a manner not differing in any important respect from those which inhabit the earth. 20. One of the most striking cir- cumstances in which the group of planets now under consideration differ from the earth and the other three which form the terrestrial or inner group is their great compara- jjjf live magnitude. The actual dia- meter of the earth is, in round numbers, 8000 miles. That of Jupiter is 88,000, that of Saturn 75,000, that of Uranus 35,000, and N that of Neptune 37,500 miles. The diameter of Jupiter is therefore 11, that of Saturn 9|, that of Ura- nus 4^, and that of Neptune 4| times the diameter of the earth. But the volumes or bulks of globes being in the proportion ot the cubes of their diameters, it follows that the bulk of Jupiter 26 SUPERFICIAL MAGNITUDE. is 1,330 times that of the earth ; and that those of Saturn. Uranus, and Neptune are respectively 857, 88, and 107 times that of the earth. To render these vast proportions more clearly perceptible, we have represented them in the annexed figures. If E (fig. 4) be imagined to represent the globe of the earth, the globe of Jupiter will be represented on the same scale by J, that of Saturn by s, that of Uranus by u, aud that of Neptune by N. 21. If they be inhabited globes analogous to the earth, they will accommodate a population as many times greater than that to which the earth is adapted, as their surfaces are greater than the surface of the earth ; and since the surfaces of globes are in the proportion of the squares of the diameters, Jupiter would afford space for habitation 121 times greater than the earth, and Saturn 90 times, Uranus 18 times, and Neptune 23 times greater. 22. It may, however, be asked whether this vast difference in the magnitude of these globes compared with that of the earth may not involve some physical consequences incompatible with the supposition of their being habitable globes at all analogous to the earth. There is but one such consequence at all conceivable. It is that the effects of gravity upon them might be such as to be altogether unfitted for species organised like those of the earth. Thus, upon the earth the average strength of a man is adapted to support and give freedom of motion and action to a body whose average weight is an hundred and a half; that of a horse to one whose average weight is half a ton, and the like ol other animals. The strength of the stalks and trunks of vege- tables is in like manner adapted to their weights. In the same manner the materials of artificial structures have a strength which has like relation to their weights. If these species, animal and vegetable, and these artificial structures were suddenly transferred to the surface of a planet, on which they would have several hundred times their present weight, the animals would not only be totally incapable of loco- motion, but they, as well as the vegetables and artificial structures, would be crushed and crumbled to pieces under the enormous pressure of their own weights. In discussing this question, it is therefore of the greatest importance to inquire whether the vast dimensions of this group of planets may not cause an increase of weight of bodies plai-ed upon their surfaces so immense as to destroy all analogy to the earth considered as an inhabited globe. In answer to this question, it may be replied that the weight of bodies placed upon the surface of a globe will depend conjointly 27 THE PLANETS, ARE THEY INHABITED ? on the quantity of matter in the globe, and on the distance of the body from its centre, which distance will be the radius or semi- diameter of the globe. The greater the quantity of matter composing the globe, the greater will be the attraction which it will exert upon a body at a given distance from its centre, But this attraction will be less as that distance is increased, in- the proportion of the square of the distance. 23. Now let us apply these principles to the major planets ; to Jupiter for example. The volume of Jupiter, as we have stated, is 1,330 times that of the earth. If it be composed of materials similar to those which compose the earth, its mass or quantity of matter will be 1,330 times greater than that of the earth, and it would conse- quently exert an attraction 1,330 times greater than terrestrial gravity upon a body at the same distance from its centre. Now, the body of an average man placed on the surface of the earth, and therefore at a distance from its centre equal to half its diameter, is attracted towards that centre with a force of 150 Ibs. The same body placed at the same distance from the centre of Jupiter would, on the above supposition, be attracted with a force of 1,330 times 150 Ibs. But bodies placed on the surface of Jupiter are at a distance from its centre eleven times greater than the semi-diameter of the earth, because the semi- diameter of Jupiter is greater than that of the earth in the proportion of 11 to 1 ; and, consequently, if the body of the man were placed on the surface of Jupiter, it would be attracted with a less force in the ratio ot the square of 11, that is of 121 to 1, The account would therefore stand thus : Ibs. Weight of a man on the surface of the earth . . 150 Weight of do. placed at a distance from Jupiter's centre equal to the semi-diameter of the earth . 150 x 1330 Weight of do. removed to Jupiter's surface, the 150x1330 distance being thus increased 11 times . . 121 If we perfoi m these arithmetical operations, multiplying 150 Ibs. by 1.330, and dividing the product by 121 we shall obtain 1,648 Ibs. Thus it appears that if the materials ot which the planet Jupiter is composed be similar to those of the earth, the weight ot a man placed upon its surface would be greater than his weight upon the earth, in the ratio of 1,648 to 150, or about 11 to 1, and of course the weights of all bodies would be greater in the same proportion. It is evident, that although such a physical condition would not at all exclude the possibility of Jupiter being an inhabited globe, 28 GRAVITY OX JUPITER. ii would require the admission, thatf the organised world upon it must be totally different from that which exists upon the earth. But Hi'-' the materials of which Jupiter is composed similar to those of the earth ? If not, the conclusion at which we have arrived must be modified. The whole question resolves itself into tlu deierminatiou of the actual quantity of gravitating matter composing this stupendous planet compared with the quantity composing the earth. Now it will be apparent, that if we could ascertain the attractions which Jupiter and the earth would exert upon bodies placed at equal distances from them, these attractions would be the exact exponents of the quantities of gravitating matter composing these two globes. Tiiis we are happily enabled to accomplish by a very simple and obvious arithmetical operation. The moon, as is well known, revolves in its monthly orbit round the earth, and is retained in that orbit by the attraction of the mass of gravitating matter composing the earth. If that mass were greater the moon would revolve faster, if less, slower. Its rate of motion is therefore an index to the quantity of gravitating matter composing the earih. Jupiter like the earth is also attended, but by four and not by one nioon. Each of these four nioons is retained in its orbit s-ound Jupiter by the attraction of the gravitating mass com- posing that planet. If it had happened that one of these four moons were at exactly the same distance from Jupiter's centre as the earth's moon is from its centre, then the motion of that moon would at once prove whether the quantity of matter com- posing Jupiter is greater or less than the quantity of matter composing the earth. If the moon of Jupiter being thus at the same distance moved faster than the earth's moon, the mass of Jupiter would be greater, and if it moved slower it would be less than the in:iss of the earth. Although all the moons of Jupiter are more distant from its centre than the moon is from the earth's centre, the nearest of these moons to Jupiter is not much more distant. Yet this moon makes a complete revolution round Jupiter in forty-two hours, while the earth's moon, though a little nearer to the attracting mass, takes nearly 656 hours to make a revolution. It is obvious, therefore, that the gravitating mass composing Jupiter must be vastly greater than that which composes the earth. By allowing for the difference of distance of the two moons from the centres of the two planets, and by taking into account the exact proportion of their velocities, it has been found that the jna.ss of gravitating matter composing Jupiter is 338^ times the i;iass of the earth. 29 THE PLANETS, ARE THEY INHABITED ? The meaning of this is, that if 338| masses of matter like the earth were placed in one scale of a colossal balance, and the single globe of Jupiter in the other, the beam would be exactly equipoised. 24. A very curious inference follows from this. It appears from what has been shown, that the volume or bulk of Jupiter is 1,330 times greater than that of the earth, so that it would require 1,330 globes like the earth to be moulded into a single globe to make such a globe as Jupiter, while 338^ such globes would be sufficient to make a globe as heavy as Jupiter. It is evident, therefore, that bulk for bulk, the matter composing Jupiter, is lighter than the matter composing the earth, in the ratio of 338| to 1,330, or what is the same, of 4 to 1. It has been proved that the earth is 5^ times the weight of an equal globe composed of water. It follows therefore that Jupiter is heavier than an equal globe of water in the far less proportion of 54? to 4, or 1| to 1. It was shown that if Jupiter were composed of matter like the earth, the weight of bodies upon his surface would be 11 times greater than upon the earth. But since it appears that it is composed of matter 4 times lighter than that of the earth, it will follow that the weight of bodies upon its surface will be 4 times less than the weight previously computed, and that it will therefore be only 2f greater than upon the earth. Thus it seems that owing to the comparative lightness of the matter composing this great globe, the attraction which it exerts upon bodies placed upon its surface, though greater than upon the earth, does not exceed terrestrial gravity in a proportion which requires the admission of any difference of organisation of the inhabitants, exceeding what may be imagined without removing Jupiter from the general analogy of the earth. 25. The other three planets of the exterior group, being attended by satellites, can be weighed against the earth by com- paring, as in the case of Jupiter, the motions of their moons with that of the earth's moon, and after making due allowance for the difference of distance, the attractions which they would severally exert, compared with that exerted by the earth, becomes the expression of the relative quantities of gravitating matter com- pared with that of the earth. It is thus found that the weight of Saturn is 101 times, that of Uranus 14, and that of Neptune 19 times the weight of the earth. It appears, therefore, that while the bulk of Saturn is 857 times greater than that of the earth, its weight is only 101 times greater. It is therefore lighter, bulk for bulk, than the earth, in the proportion of 101 to 857, or 1 to 8J. 30 GRAVITY ON SATURN AND URANUS. In like manner, while the bulk of Uranus is 82 times greater, its weight is only 14 times greater than that of the earth. It is therefore lighter, bulk for bulk, than the earth, in the propor- tion of 14^ to 82, or 1 to 6 very nearly. In fine, while the bulk of Neptune is 107 times greater, its weight is only 19 times greater than the earth, and it is therefore lighter, bulk for bulk, than the earth, iu the proportion of 19 to 107, or nearly 1 to 6, the same as Uranus. It has been proved that the earth is, bulk for bulk, 5^ times heavier than water. It follows therefore that Saturn being 8^ times lighter, bulk for bulk, than the earth, is lighter, bulk for bulk, thau water in the proportion of 5^ to 8, or 1 to 1^. In like manner it appears that Uranus and Neptune, being- nearly six times lighter, bulk for bulk, than the earth, must be composed of materials equal in weight, bulk for bulk, with water. The weight of Jupiter is equal to that of some of the denser sorts of wood, such as lignum vitee or ebony, and that of Saturn is equal to the weight of the lighter sorts, such as deal. 26. The weight of bodies placed upon the surfaces of Saturn, Uranus, and Neptune, are ascertained by comparing their masses with their magnitude, as in the case of Jupiter, and it is thus found that it does not differ much from their weights on the earth. On Saturn it is a very little more, and on Uranus and Neptune a little less. 27. It appears, therefore, that if these planets be inhabited, the same organisation which prevails on the earth would be sufficient to impart the same, or nearly the samp, degree of stability and freedom of locomotion. A man, in fine, transferred from the earth to Saturn, Uranus, or Neptune, would not be sensible of much difference in his power of action and motion. Trees and other vegetables, with their present strength, would be equally stable, and artificial structures equally solid and durable. 28. The importance of the atmosphere to all the functions of animal and vegetable life, and its uses in the diffusion of light and the retention and diffusion of heat, have been fully explained. The existence of any atmosphere on a planet is, therefore, an essential condition necessary to bring it into analogy with the earth as an inhabited globe. The atmospheres of Jupiter and Saturn are rendered con- spicuously apparent by the telescope. We see the clouds floating in dense masses upon them ; so dense indeed and so unbroken as to conceal from our view the characters of the surfaces of the planets themselves. Uranus and Neptune are too remote for like observations in the present state of the telescope, but it is in the highest degree 31 THE PLANETS, ARE THEY INHABITED ? probable that with improved powers of that instrument, like -appearances will be observed upon them. 29. It might be imagined that the circumstance of being thus constantly eirveloped in clouds would render it impossible to ascertain whether these planets, like the earth, turn upon an -axis, and consequently have days and nights analogous to those of the earth. It must be remembered, however, that the earth's atmosphere, and the clouds which float upon it, partake of the motion of diurnal rotation, and that if the atmosphere were perfectly calm for twenty-four hours, the various masses of clouds resting upon it being always suspended over the same parts of its surface, would be carried round with it, and would consequently make a complete rotation round the common axis in the same time exactly as the solid globe of the earth. Now, if an observer placed upon any of the planets, not too remote, were in this case to direct a sufficiently powerful telescope to the earth, although he might not see the outlines of land and water, being enveloped by clouds, he would distinguish the masses of clouds themselves by their varieties of light and shade, -dud would see them carried round by the diurnal rotation dis- appearing at one side and reappearing at the other ; and he would thus not only ascertain the fact of the diurnal rotation of the earth, but also the time of rotation, that being the interval between two successive disappearances or reappearances of the same lineaments of light and shade, anil the direction of the axis of rotation that direction being at right angles to the apparent motion of rotation. Circumstances, just such as these, have been observed to take place on Jupiter and Saturn. The masses of cloud, whose lights and shadows diversify their surfaces, though more or less shifting and variable, are at times found to remain fixed, as if the atmosphere were absolutely calm and quiescent for intervals sufficiently protracted to enable the telescopic observer to see the same lineaments disappear at one side of the disk, reappear at the other, and passing across the disk, again disappear. These are the obvious effects of the rotation of these planets upon an axis at right angles to the direction of this apparent motion. Observations such as these, repeated and continued for long periods of time, have led to the discovery that Jupiter turns upon a certain diameter with a diurnal motion, making a complete revolution in 9 h 55 m 26' terrestrial time, and that Saturn revolves in like manner, and what is more remarkable in a time not very different from that of the rotation of Jupiter. Saturn's rotation is completed ill 10 h 29'" 17 s . 32 MABS. SKETCH OF THE OUTLINES OF CONTINENTS AND OCEANS, AND THE SNOW REGION OF THE POLAR CTRCLE OF THE NORTHERN HEMISPHERE OF THE PLANET MARS, FROM THE OBSERVATIONS OF MAPLER. THE PLANETS: ARE THEY INHABITED WORLDS? CHAPTER III. Diurnal rotation of Framis. 2. Inclination of the axes and limitation of the seasons on the Major planets. 3. Jovian zones and climates. 4. Saturnian. 5. Short days and nights of Major planets. 6. Lightness of their materials. 7. Oceans and seas must consist of a liquid lighter than water. 8. Jovian, Saturnian, and Uranian years. 9. Effects of diurnal rotation on the distribution of clouds. 10. These effects more conspicuous in the Major planets. 11. Mani- fested by the belts. 12. Telescopic appearance of Jupiter. 13. Herschel and Madlefs telescopic views of Jupiter. 14. Jupiter elliptical in form. 15. Discovery of Jupiter's moons. 16. Short months. 17. Lunar eclipses. 18. Telescopic appearance of Jupiter's satellites. 19. As seen from Jupiter. 20. The Saturnian system. 21. Atmosphere and moons. LARDKBE'S MUSEUM OP SCIKSCK, No. 6. D 33 THE PLANETS, ARE THEY INHABITED ? 1. CONCLUSIVE and satisfactory observations of tins kind have not yet been made on Uranus, but from the observations, imper- fect as they are which have been made, there are probable grounds for the inference that this planet also revolves on an axis in nine hours and a half. Thus it appears that these vast globes, revolving at distances from the sun from five to thirty times that of the earth, have like the earth alternations of light and darkness ; that they have days and nights ; that all parts of their surfaces are in turn, like those of the earth, presented to the common centre of light and warmth, but that the intervals which regulate these alternations, " the division of the light from the darkness," which has been found good by Divine beneficence for the races which inhabit the earth, has not been found " good " for those which inhabit those more remote worlds. The average length of the day on them is about five hours, while it is twelve upon the earth. The creatures placed upon these planets must, therefore, be so constituted as to require more frequent intervals for rest and sleep, and shorter periods of wakefulness, activity, and labour, than those which inhabit the earth. 2. The position of the axis of rotation has been ascertained in the cases of Jupiter and Saturn, but not as yet of the other two planets of this group. The axis of Jupiter is inclined to the plane of its orbit at the very small angle of 3 5' 30", while that of the earth, as is well known, has an inclination of 23 28' 30". As this inclination limits the temperature of the seasons, the extent of the zones and the varieties of the climates, it follows, that on Jupiter these phenomena must be very different from those of the earth, The extreme variation of the altitude of the sun at noon does not much exceed six degrees in any latitude, a change which cannot produce any very sensible variation in the temperature of the seasons. On this planet there is, therefore, perpetual spring. 3. The tropics of Jupiter are only three degrees north and south of his equator, and the polar circles, which include the only parts of the planet at which the sun remains at any time below or above the horizon during a complete revolution, are limited to three degrees around the poles. In fine, the diurnal phenomena on Jupiter are, at all times, nearly the same as they are upon the earth at the Equinoxes. 4. The case is very different with Saturn, which presents a closer analogy to the earth. The direction of the diurnal motion, in the case of that planet, makes an angle of 26 48' 40", with the plane of the orbit differing little from the angle which the ecliptic 34 DAYS, NIGHTS, AND SEASONS. makes with" the terrestrial equator. The Saturnian seasons^ zones, and_clim.ates are, therefore, absolutely similar to those of the earth. The tropical and polar phenomena are the same. It is to be hoped that the recent improvements effected by Lord Rosse, in the construction of reflecting telescopes, may place it within the power of observers to determine the position of the axes of Uranus and^Neptune, and the line of rotation of the latter. 5. So far as discovery has hitherto proceeded, it would appear that a comparatively greater rapidity of rotation, and shorter intervals of light and darkness, is a characteristic by which the group of major planets are distinguished from the terrestrial group. 6. A second striking distinction between these two groups is the comparative lightness of the matter composing the former. It will be remembered that, in our notice of the terrestrial group, we showed that the density of the matter composing the earth, Venus, and Mars is nearly equal, and is five-and-a-half times that of water, and about the same as that of iron-stone, while the density of the planet Mercury is equal to that of gold. Now, it appears that, on the contrary, the density of Jupiter very little exceeds that of water, that of Uranus and Neptune is exactly that of water, while Saturn is so light that it would float in water like a globe of pine-wood. It must be admitted to be not the least striking among the wondrous results of human sagacity, that these remote globes have been submitted to such an analysis as enables us thus to pro- nounce with certainty upon one, at least, of the physical characters of their constituent parts. In some instances science has even gone further, and has shown that the densities of Jupiter and Saturn cannot be uniform, but must increase gradually as that of the earth is known to do, from the surface to the centre, and from this it follows that the mean density of the matter of their surface must be much less than that of water. 7. It follows, therefore, that the seas and oceans of these planets must consist of a liquid far lighter than water. It is computed that a liquid on Jupiter, which would be analogous to the terrestrial oceans, would be three times lighter than sul- phuric ether, the lightest known liquid, and would be such that cork would scarcely float in it. 8. The rapid rotation of these planets, combined with the great length of their revolution round the sun, gives them years consisting of a vast number of days. The year of Jupiter is nearly twelve terrestrial years, or, more exactly, 4332^ ter- restrial days. But as the Jovian days are shorter than the *2 35 THE PLANETS, AKE THEY INHABITED \ terrestrial in the ratio of 1 to 2*42, it follows that in a Jovian year there are 10485 Jovian days. The Saturnian year is equal to 29| terrestrial years, or more exactly to 10,759 terrestrial days, and since the Saturnian day is shorter than the terrestrial in the ratio of 1 to 2'3, it will follow that the Saturnian year consists of 24746 Saturnian days. Thus each of the Saturnian seasons, spring, summer, autumn, and winter is equal to seven-and-a-half terrestrial years. The TJranian year is equal to 84 terrestrial years, or 30687 terrestrial days ; and the TJranian day, according to the probable estimate, being shorter than the terrestrial day in the ratio of 1 to 2^, it follows that the Uranian year consists of 77336 Uranian days. If the axis of Uranus be inclined to the plane of its orbit like that of Saturn, its seasons will be similar to those of the earth, but of very different duration, their length being 21 terrestrial years, or 19334 Uranian days. 9. One of the most remarkable meteorological consequences of the diurnal rotation of the earth is the system of atmospheric currents, which, in both hemispheres, are directed generally parallel to the equator, and which, from their great permanence and regularity in the lower latitudes, have, in all ages since the invention of ocean navigation, subserved the purposes of com- merce so extensively as to have acquired the name of the trade- winds. These phenomena will be explained more fully, so far as relates to their physical causes, in another part of this series. What we now desire to direct attention to is their effects in the upper strata of the atmosphere. It is evident that such currents must have a general tendency to distribute the strata of clouds in lines or streaks, more or less pronounced, according to their intensity and regularity, parallel to the equator. If these aerial currents were much more intense and much more permanent and regular, and if the clouds them- selves were more voluminous and permanent than they are, this distribution of them in streaks or layers at right angles to the earth's axis would be in proportion more pronounced, more regular, and more permanent. The causes of these atmospheric currents are traced to the combined effects of the velocity with which the atmosphere is carried round with the earth on its axis, and the influence of the solar heat produced upon the zone of atmosphere over those regions of the globe which extend to a certain distance north and south of the equator. If the velocity with which the atmosphere is carried round were much greater than it is, and if the atmosphere were more 36 TRADE WINDS AND BELTS. constantly and heavily loaded with clouds, these effects would be much more striking. The velocity with which the atmosphere is carried round would be greater if the earth's rotation were more rapid. It would also be greater, even with the present rate of rotation, if the earth were a larger globe, because then the atmosphere would be carried in the same time round a proportionately greater circumference. But if both these conditions were at the same time fulfilled if the earth revolved more rapidly on its axis, and were at the same time a larger globe, the atmosphere would be not only carried round in a less time, but would revolve through a larger circumference. 10. NoW this is exactly the case with the major planets. Jupiter, Saturn, and Uranus make each about five revolutions on their axes while the earth makes two, and the equatorial circum- ference of Jupiter is eleven times, that of Saturn above nine times, and that of Uranus more than four times greater than the equatorial circumference of the earth. The speed with which the equatorial zone of air is whirled round on Jupiter is therefore about 27 times, on Saturn 23 times, and on Uranus about 7 times greater than on the earth. We find by telescopic observation also, as has been already stated, that the atmospheres of these planets are so thickly and constantly, loaded with clouds that the surfaces of the solid globes are permanently concealed from us. It may, therefore, be inferred that the prevalence of atmo- spheric currents on these planets parallel to their equators are far more constant and more strong than upon the earth ; and since the masses of cloud with which they are loaded are greater and more permanent, the effects of such currents upon their distribution in equatorial strata or bands must be supposed to be far more conspicuous. 11. Observation has confirmed this in a most remarkable and interesting manner. Look at the six telescopic views of Jupiter, given in figures 1 to 6 (page 38), which are engraved after the telescopic drawings of Herschel and Madler. The streaks parallel to the Jovian equator are conspicuous. These streaks, which were seen not long after the invention of the telescope, are called " Jupiter's Belts." Of all the bodies of the system, the moon perhaps alone excepted, Jupiter presents to the telescopic observer the most magnificent spectacle. Notwithstanding its vast distance, such is its stupendous magnitude that it is seen under a visual angle nearly twice that of Mars. A telescope of a given power, there- fore, shows it with an apparent disc four times greater. It has 37 1. Sept. 23, 1832. 4. Jan. 2, 183(5. 38 SIX TELJCSCOMC VIEWS OF JUPITER. 2. Dec. 23, 1834. 3. Dec. 23, 1834. 5. .an. It), 1636. 6. Jan. 17, 1836. VIEWS OF JUPITER. consequently, been submitted to examination by the most emi- nent observers, and its appearances described with great minute- ness of detail. The apparent diameter in opposition (when it is on the meridian at midnight) is about the fortieth part of that of the moon, and therefore a telescope with the very moderate magnifying power of forty, presents it to the observer with a disc equal to that with which the full moon is seen with the naked eye. A power of four or five is sufficient to enable the observer to see the planet with a sensible disc ; a power of thirty shows the more prominent belts ; a power of forty shows it with a disc as large as that which the full moon presents to the naked eye ; but to be enabled to observe the finer streaks which prevail at greater distances from the planet's equator, it is not only necessary to see the planet under favourable circumstances of position and atmosphere, but to be aided by a well-defining telescope with magnifying powers varying from 200 to 300. The planet, when thus viewed, appears to exhibit a disc, the ground of which is a light yellowish colour, brightest near its equator, and melting gradually into a leaden-coloured gray towards the poles, still retaining, nevertheless, somewhat of its yellowish hue. Upon this ground are seen a series of brownish- gray streaks, resembling in their form and arrangement the streaks of clouds which are often observed in the sky on a fine calm evening after sunset. The general direction of these streaks is parallel to the equator of the planet, though sometimes a departure from strict parallelism is observable. They are not all equally conspicuous or distinctly defined. Two are generally strikingly observable, north and south of the equator, separated by a bright yellow zone, a part of the general ground of the disc. These principal streaks commonly extend around the globe of the planet, being visible without much change of form during an entire revolution of Jupiter. This, however, is not always the case, for it has happened, though rarely, that one of these streaks, at a certain point, was broken sharply off, so as to present to the observer an extremity so well defined and unvarying for a considerable time as to supply the means of ascertaining, with a very close approximation, the time of the planet's rotation. The borders of these principal streaks are sometimes sharp and even, but, sometimes (those especially which are further from the equator), rugged and uneven, throwing out arms and offshoots. On the parts of the disc more remote from the equator, the streaks are much more faint, narrower, and less regular in their parallelism, and can seldom be distinctly seen, except by 'THE PLANETS, ARE THEY INHABITED 1 practised observers, with good telescopes. With, these, how- ever, what appears near the poles, in instruments of inferior power, as a dim shading of a yellowish-gray hue, is resolved into a system of fine parallel streaks in close juxtaposition, which becoming closer in approaching the pole, finally coalesce. In general, all the streaks become less and less distinct towards either the eastern or western limb, disappearing alto- gether at the limb itself. Although these streaks have infinitely greater permanency than the arrangements of the clouds of our atmosphere, and are even more permanent than is necessary for the exact deter- mination of the planet's rotation, they are nevertheless entirely destitute of that permanence which would characterise Zeno- graphic features, such as are observed, for example, on Mars. The streaks, on the contrary, are subject to slow but evident variations, so that after the lapse of some months the appearance of the disc is totally changed. 12. These general observations on the appearance of Jupiter's disc will be rendered more clearly intelligible by reference to the telescopic drawings of the planet given in fig. 1 to 6. In fig. 1 is given a telescopic view of the disc by Sir John Herschel, as it appeared in the 20-fret reflector at Slough on the 23rd September, 1832. The other views were made by M.Madler from observations taken in 1835 and 1836, at the dates indicated on the plate. The two black spots represented in figs. 2, 3, and 4, were those by which the time of rotation was determined. They were first observed by Madler, on the 3rd November, 1834. The effect of the rotation on these spots was so apparent that their change of position with relation to the centre of the disc, in the short interval of five minutes, was quite perceivable. A third spot, much more faint than these, was visible at the same time, the distances separating the spots being about 24 of the planet's surface. It was estimated that the diameter of each of the two spots represented in the diagrams was 3,680 miles, and the distance between them was sometimes observed to increase at the rate of half a degree, or 330 miles, in a month. The areas of these spots must therefore have been nearly equal to a fourth part of the entire surface of the earth. The two spots continued to be distinctly visible from the 3rd of November, 1834, when they were first observed, until the 18th of April, 1835 ; but during this interval the streak on which they were placed had entirely disappeared. It became gradually fainter in January (see fig. 4), and entirely vanished in February : the spots, how- ever^ retaining all their distinctness. The planet, after April, passing towards conjunction, was lost in the light of the sun j 40 VIEWS OF JUPITER. and when it re-appeared in August, after conjunction, the spots had altogether vanished. The observations being continued, the drawings (figs. 5 and 6), were made from observations on the 16th and 17th of January, 1836, when the entire aspect of the disc was changed. The two figures (5 and 6) represent opposite hemispheres of the planet. It was remarked that the two spots, when carried round by the rotation, became invisible at 55 to 57 from the centre of the disc. This is an effect which would be produced if the spots were openings in the mass of clouds floating in the atmo- sphere of the planet. Their disappearance on moving from the centre of the disc would be caused by their deep sides inter- cepting the view of their bottom, just as we should lose sight of a railway in a deep cutting, if, being placed at the edge of the cutting, we were to withdraw to some distance from it. A proper motion with a slow velocity, and in a direction con- trary to the rotation of the planet, was observed to affect the spots, and this motion continued with greater uniformity in March and April, after the disappearance of the belt. It was calculated that the velocity of their proper motion over the surface of the planet was at the rate of from three to four miles an hour. Although the two black spots were not observed by Madler until the first days of November, they had been previously seen and examined by Schwabe, who observed them to undergo several curious changes, in oue of which one of them disappeared for a certain interval, its place being occupied by a mass of fine dots. It soon, however, re-appeared as before. From all these circumstances, and many others developed in the course of his extensive and long-continued observations, Madler considers it highly probable, if not absolutely certain, these vast masses of clouds have a permanence of form, position, and arrangement to which there is nothing analogous in the atmo- sphere of the earth, and that such permanence may in some degree be explained by the great length and very small variation of the seasons. He thinks it probable that the inhabitants of places in latitudes above 40 never behold the firmament at all, and those in lower latitudes only on rare occasions. It is also probable that the bright yellowish general ground of Jupiter's disc consists of clouds, which reflect light much more strongly than the most dense masses which are seen illuminated by the sun in our atmosphere ; and that the darker streaks and spots observed upon the disc are portions of the atmosphere, either free from clouds and through which the surface of the planet is visible more or less distinctly, or clouds of less THE PLANETS, ARE THEY INHABITED ? density and less reflecting power than those which float over the general atmosphere and form the ground on which the belts and spots are seen. That the atmosphere has not any very extraordinary height above the surface of the planet is proved by the sharply denned edge of the disc. If its height bore any considerable proportion to the diameter of the planet, the light towards the edges of the disc would become gradually fainter, and the edges would be nebulous and ill-defined. The reverse is the case. 13. One of the most remarkable consequences of the rotatory motion, which has been the means of giving to the inhabitants of the earth the alternations of day and night, is that its figure has been changed from that of a perfect sphere to an oblate spheroid ; that is, a globe flattened at the poles. This has been already explained. If the diurnal rotation of the earth were more rapid than it is, this polar flattening would be more considerable. In short, the degree of oblateness, or the proportion in which the polar axis is shorter, than the equatorial diameter, depends on the time of rotation in such a manner, that this time being known, that pro- portion can be computed, or vice versd. Now, the rotation of these major planets being ascertained, and being much more rapid than that of the earth, it would follow that they must be oblate spheroids, and that their degree of oblateness must be much greater than that of the earth. Observation fully confirms this. The disc of Jupiter, seen with magnifying powers as low as 30, is evidently oval, the lesser axis of the ellipse coinciding with the axis of rotation, and being perpendicular to the general direction of the belts ; as in the case of the earth, the degree of oblateness of Jupiter is found to be that which would be produced upon a globe of the same magnitude, having a rotation such as the planet is observed to have. At the mean distance from the earth, the apparent diameters of the disc are ascertained by exact micrometric measures to be Miles. Equatorial Diameter . . . . . 38 '4 "=92080 Polar Diameter , 35'6" = 85210 Mean Diameter . . . =88645 The polar diameter is therefore less than the equatorial, in the ratio of 356 to 384, or 100 to 108 nearly. Other estimates give the ratio as 100 1o 10^ 42 OBLATE FORK AND SATELLITES. This is just the proportion which would be produced by a rotation like that which Jupiter is ascertained to have. 14. However agreeable may be the light of the moon in the absence of the sun, that attendant is not indispensable to the well-being of the inhabitants of the earth ; and of the inner group 1 of planets the earth alone has been supplied with such a supplement to the solar illumination. The planets constituting the outer group are, however, much more munificently provided with this convenience, each being supplied with so many moons that their nights must be per- petually moonlit. When Galileo directed the first telescope to the examination of Jupiter, he observed four minute stars, which appeared in the line of the equator of the planet. He took these at first to be fixed stars, but was soon undeceived. He saw them alternately approach to and recede from the planet, observed them pass behind it and before it, and oscillate, as it were, to the right and left of it, to certain limited and equal distances. He soon arrived at the obvious conclusion that these were bodies which revolved round Jupiter in orbits, at limited distances, and that each successive body included the orbit of the others within it ; in short, that they formed a miniature of the solar system, in which, however, Jupiter himself played the part of the sun. As the telescope improved, it became apparent that these bodies were small globes, related to Jupiter in the same manner exactly as the moon is related to the earth ; that, in fine, they were a system of four moons, accompanying Jupiter round the sun. 15. But connected with these appendages there is perhaps nothing more remarkable than the period of their revolutions. That moon which is nearest to Jupiter completes its revolution in forty-two hours. In that brief space of time it goes through all its various phases ; it is a thin crescent, halved, gibbous, and fulL It must be remembered, however, that the day of Jupiter, instead of being twenty-four hours, is less than ten hours. This moon, therefore, has a month equal to a little more than four Jovian days. In each day it passes through one complete quarter ; thus, on the first day of the month it passes from the thinnest crescent to the half moon; on the second, from the half moon to the full moon ; on the third, from the full moon to the last quarter ; and on the fourth returns to con- junction with the sun. So rapid are these changes that they must be actually visible as they proceed. The apparent motion of this satellite in the firmament of Jupiter is at the rate of more than 6 per hour, and is the same as if our moon were to move over a space equal to her own THE PLANETS, AEE THEY INHABITED ? apparent diameter in rather less than four minutes. Such an object would serve the purpose of the hand of a stupendous celestial clock. The second satellite completes its revolution in about eighty- five terrestrial hours, or about eight and a half Jovian days. It passes, therefore, from quarter to quarter in twenty-one hours, or about two Jovian days, its apparent motion in the firmament being at the rate of about 4'25 per hour, which is as if our moon were to move over a space equal to nine times its own diameter per hour, or over its own diameter in less than seven minutes. The movements and changes of phase of the other two moons are not so rapid. The third passes through its phases in about 170 hours, or seventeen Jovian days, and its apparent motion is at the rate of about 1 per hour. The fourth and last completes its changes in 400 hours, or forty Jovian days, and its apparent motion is at the rate of little less than 1 per hour, being double the apparent motion of our moon. Thus the inhabitants of Jupiter have four different months, of four, eight, seventeen, and forty Jovian days respectively. 16. Jupiter's moons differ from that of the earth, inasmuch as all of them move in the plane of the planet's equator, from which plane the sun can never depart further than about 3. At and for a considerable time before and after the Jovian equinoxes, the sun is so very near the planet's equator that each of the moons, which never leave that equator, must necessarily pass between the sun and the planet every revolution. It follows, therefore, that for a long interval before and after each of the equinoxes, solar eclipses will be produced by each of the four moons every revolution. These eclipses, however, will be visible only at certain low latitudes. The inhabitants of the higher latitudes in either hemisphere will be so far removed from the common direction of the moons and sun, or what is the same, from the plane of the Jovian equator, that the visual line directed to the sun will be clear of the moons. The shadow of this vast globe is so prodigious in its dimen- sions that the three inner moons never pass behind Jupiter without passing through it. They are therefore invariably eclipsed every revolution ; and since at the time these moons would appear full they are in direct opposition to the sun, they are then plunged in the shadow, and therefore eclipsed. The Jovians consequently never see any of these three moons when they are full. The fourth or most remote of the moons is, like the others, generally eclipsed every revolution ; but at the Jovian seasons of midsummer and midwinter, for a certain interval, the sun, aiid 44 JOVIAN ECLIPSES. consequently the shadow of the planet, are sufficiently removed from the plane of the planet's equator to enable this moon to clear the boundary of the shadow, and to pass through oppo- sition without entering it. This is the only case in which any of the moons can ever pass through opposition without also passing through the shadow of the planet, and consequently the only times the Jovians ever enjoy the spectacle of a full moon. When these circumstances are combined with the rapid revo- lution of the moons, it will be easily understood that the celestial phenomena of the Jovians must offer great variety, and that their chronology must be curiously complicated. A total lunar eclipse of the first or nearest moon must take place every forty- two terrestrial hours, that is, every fourth Jovian day ; and for a long interval before and after the equinoxes a total or partial solar eclipse must take place at like intervals, being alternated with the lunar eclipses, and separated from them by intervals of only twenty-one terrestrial hours, or two Jovian days. The same phenomena exactly take place with relation to the second satellite, at intervals of 3^ terrestrial, or about 8^ Jovian days ; to the third at intervals of 7 terrestrial, or 17 Jovian days ; and to the fourth at intervals of 16^ terrestrial, or 40 Jovian days, subject, nevertheless, with respect to the last, to an interruption at the Jovian summer and winter, from the cause already explained. 17. The appearance which the satellites of Jupiter present when viewed with a telescope of moderate power, is that of minute stars ranged in the direction of a line drawn through the centre of the planet's disc, nearly parallel to the direction of the belts, and therefore coinciding with that of the planet's equator. The entire system is comprised within a visual area of about two-thirds of the apparent diameter of the moon. If, therefore, we conceive the moon's disc to be centrically superposed on that of Jupiter, not only would all the satellites be covered by it, but that which elongates itself most from the planet would not approach nearer to the moon's edge than one-sixth of its apparent diameter. If all the satellites were at the same time at their greatest apparent distances from the planet, they would, relatively to Fig. 7. the apparent diameter of the planet, present the appearance represented in fig. 7. THE PLANETS, ARE THEY INHABITED ? By comparing their real diameters with their distances, the apparent diameters of the several satellites, as seen from Jupiter, may be easily ascertained. 18. The first satellite has an apparent diameter equal to that of the moon ; the second and third are nearly equal and about half that diameter ; and the apparent diameter of the other satellite is about the fourth part of that of the moon. It may be easily imagined what various and interesting nocturnal phenomena are witnessed by the inhabitants of Jupiter, when the various magnitudes of these four moons are combined with the quick succession of their phases and the rapid apparent motions of the first and second. The motions of the first three satellites are so related that they never can be at the same time on the same side of Jupiter ; so that whenever any one of them is absent from the Jovian firmament at night, one at least of the others must be present. The nights are, therefore, always moonlit, except during eclipses, and often enlightened at once by three moons of different apparent magnitudes, and seen under different phases. 19. Of all the planets either of this or the terrestrial group, that which presents to the astronomical observer the most astonishing spectacle is Saturn a stupendous globe, nearly 900 times greater in volume than the earth, surrounded by two, at least, and probably by several thin flat rings of solid matter, outside which revolve a group of eight moons ; this entire system moving with a common motion so exactly maintained that no one part falls upon, overtakes, or is overtaken by another in their course around the sun. Such is the SATURNIAN SYSTEM, the central body of which was known as a planet to the ancients, the annular appendages and satellites being the discovery of modern times. The distance of Saturn from the sun is so enormous that if the whole earth's orbit, measuring nearly 200,000000 of miles in diameter, were filled with a sun, that sun seen from Saturn would be only about 24 times greater in its apparent diameter than is the actual sun seen from tha/earj^ A cannon-ball moving at 500 miles an hour would take -0.1 00(3 j?eajs^ and a ^ railway train moving 50 miles an hour would take 10000 years to move from Saturn to the sun. Light, which moves at the rate of nearly 200000 miles per second, takes 4. days 1^ hours' and /S 3 minutes to move over the same distance. Yet to this distance solar gravitation transmits its mandates, and is obeyed with the utmost promptitude and the most unerring precision. Taking the diameter of Saturn's orbit at 1800,000000 of miles, its circumference is 5650,000000 of miles, over which it 46 SATURNIAN SYSTEM. moves in 10759 days. Its daily motion is therefore 525140 miles, and its hourly 21880 miles. 20. All that has been said above respecting the atmosphere, the diurnal rotation, and their consequences, the clouds, atmospheric currents, trade-winds, and oblate figure in the case of Jupiter, may be applied without any important modification to Saturn. This planet is attended by eight moons, four of which, like those of Jupiter, are remarkable for their proximity to the planet, three being at distances considerably less than that of the terrestrial moon from the earth, and the fourth at nearly the same distance. Of the four other moons, the most remote is ten times further from Saturn than the terrestrial moon is from the earth, and the nearest is about one half more distant. The distances of moons are, however, more justly estimated relatively to the planets they attend, by expressing them in semi-diameters of the planet. If thus expressed, the moons of Saturn are on a scale of distance very much less than that of the terrestrial moon. The distance of the most remote is 64 semi-diameters of Saturn, while that of the nearest is little more than 3 semi-diameters. The distance of the terrestrial moon from the earth is 60 semi-diameters. Great, however, as these distances are, they are reduced to a very small apparent measure, owing to the remoteness of the Saturnian system from^the earth. If the centre of the terres- trial moon were to come upon the centre of Saturn's disc, the most remote of his satellites could not approach nearer to the edge of the moon's disc than one-third of the moon's semi- diameter. Thus, although the Saturnian system fills a space measuring about 5,000000 of miles in its extreme breadth, this entire space would be covered by the moon's disc, even if that disc had a diameter one-third less than its actual diameter. All that has been said of the phases and appearances of the moons of Jupiter, as presented to the inhabitants of that planet, is equally applicable to the satellites of Saturn, with this dif- ference, that instead of four, there are eight moons continually revolving round the planet, and exhibiting all the monthly changes to which we are accustomed in the case of the solitary satellite of the earth. The periods of Saturn's moons, like those of Jupiter, are short, with the exception of those most remote from the primary. The nearest passes through all its phases in 22^ hours, and the fourth, counting outwards, in less than 66 hours. The next three have months varying from 4 to 22 terrestrial days. These seven moons move in orbits whose planes are nearly 47 THE PLANETS, ARE THEY INHABITED \ coincident with, the plane of the Saturnian equator. The conse- quence of this arrangement is, that they are always visible by the inhabitants of both hemispheres when they are not eclipsed by the shadow of the planet. The motion of the nearest moon is so rapid as to be per- ceivable by the Saturnians like that of the hour-hand of a colossal timepiece. It describes 360 in 22J hours, being at the rate of 16 per hour, or 16' per minute, so that in two minutes it moves over a space equal to the apparent diameter of the moon. The eighth, or most remote satellite, is in many respects ex- ceptional, and different from all the others. Unlike these, it moves in an orbit inclined at a considerable angle to the plane of the equator. Owjing to the great distance of Saturn, the dimensions of the satellites have not been ascertained. The sixth in order, proceed- ing outwards, called Titan, is, however, known to be the largest, and it appears certain that its volume is little less than that of the planet Mars. The three satellites immediately within this, Ehea, Dione, and Tethys, are smaller bodies, and can only be seen with telescopes of. great power. The two nearest, Enceladus, and Mimas, require instruments of the very highest power and perfection, and atmospheric conditions of the most favourable nature, to be observable at all. The real magnitudes of the satellites, the sixth excepted, being unascertained, nothing can be inferred with any certainty respecting their apparent magnitudes as seen from the surface of Saturn, except what may be reasonably conjectured upon analogies to other like bodies of the system. The satellites of Jupiter being all greater than the moon, while one of them exceeds Mercury in magnitude, and another is but little inferior in volume to that planet, it may be assumed with great probability of truth that the satellites of Saturn are at least severally greater in their actual dimensions than our moon. 48 SATURX, AS SEEN IN NOVEMBER, 1852, WITH A REFRACTOR OF 6 INCH APERTURE AT WATERINGBURY NEAR MAIDSTONE, BY W. R. DAWES. THE PLANETS : ARE THEY INHABITED WORLDS] CHAPTER IY. 1. Apparent magnitudes of the moons as seen from Saturn. 2. Their phases Short Saturnian months. 3. Solar and lunar eclipses. 4. Discovery of the rings. 5. Phases of the rings as seen from the earth. 6. Their appearance when seen edgeways in 1848 Schmidt's drawings of them. 7. Mountains upon them. 8. Their dimensions. 9. Discovery of the obscure semi-reflective rings. 10. Dawes' telescopic view of the planet and rings. 11. Appearance of the rings as seen from Saturn. 12. Errors committed on this subject by Bode, Herschel, Madler, and others. 13. Correction of these errors. 14. Appearance of rings will vary with the latitude of the observer. 15. Illustrative diagrams. 16. Recapitulation. 17. No difficulty can arise in admitting the possibility of differently organised tribes on the different planets. 18. The sun, its physical character incom- patible with habitability. 19. The moon not habitable. 20. Nor the satellites. 21. Comets not habitable. 22. The planetoids er asteroids. LARDNER'S MUSEUM OF SCIENCE. No. 10 49 THE PLANETS, ARE THEY INHABITED I 1. If the estimate of the real magnitudes of the satellites, given at the conclusion of the last chapter, be admitted, their probable apparent magnitudes as seen from Saturn may be inferred from their distances. The distance of the first, Mimas, from the nearest part of the surface of the planet, is only 94,000 miles, or about 2| times less than the distance of the moon ; the distance of the second is about half that of the moon ; that of the third about two-thirds, and that of the fourth about five-sixths, of the moon's distance. If these bodies, there- fore, exceed the moon in their actual dimensions, their apparent magnitudes as seen from Saturn will exceed the apparent magnitude of the moon in a still greater ratio than that in which the distance of the moon from the earth exceeds their several distances from the surface of Saturn. Of the remaining satellites, little is as yet known of the seventh, Hyperion, which has only been recently discovered ; and the great magnitude of the sixth, Titan, renders it probable that, notwithstanding its great distance, it may still appear to the Saturnians with a disc as great as that of the terrestrial moon. 2. All that has been observed respecting the remarkable appearances presented by the rapidly varying phases of Jupiter's moons is equally applicable to Saturn ; the spectacle, however, being enriched and varied by twice the number of moons. Since the first satellite changes from the thinnest crescent to the half moon in five hours and a half (terrestrial), the gradual change of phase must be as visible as the motion of the hand of a timepiece. The second changes at a rate only one-half slower, that is, it passes from a thin crescent to the half moon in eight hours. The first passes from the state of the new to that of the full moon in eleven, and the second in sixteen hours. The interval between new and full moon for the third is twenty-two hours ; for the fourth, thirty-two hours ; for the fifth, fifty-three ; for the sixth, eight terrestrial days ; for the seventh, eleven ; and for the eighth, forty. 3. The eclipses, solar and lunar, produced and suffered by these eight satellites are not so frequent and regular as those described as taking place in the Jovian system, because Saturn's equator is inclined to the sun's course at an angle of nearly 27, con- siderably greater than the obliquity of the ecliptic, the conse- quence of which is that the sun, at and near the Saturnian midsummer and midwinter, departs to a great apparent distance from the equator, to which the motion of the satellites (except the eighth) is confined. For the same reason, the satellites depart further from the centre of the shadow, and all except the nearer ones generally move clear of the shadow in 50 STRUCTURE OF SATURN'S KINGS. opposition. The Saturnians, therefore, have the advantage over the Joviaus of witnessing the frequently recurring spectacle of several full moons in their firmament. 4. The invention of the telescope having invested astrono- mers with the power of approaching, for optical purposes, hun- dreds of times closer to the objects of their observation, one of the earliest results of the exercise of this improved sense was the discovery that the disc of Saturn differed in a remarkable manner from those of the other planets in not being circular. It seemed at first to be a flattened oblong oval, approaching to the form of an elongated rectangle, rounded off at the corners. As the optical powers of the telescope were improved, it assumed the appearance of a great central disc, with two smaller discs, one at each side of it. These lateral discs, in fine, took the appearance of handles or ears, like the handles of a vase or jar, and they were accordingly called the ansse of the disc, a name which they still retain. At length, in 1659, Huygens explained the true cause of this phenomenon, and showed that the planet is surrounded by a ring of opaque solid matter, in the centre of which it is suspended, and that what appear as ansae are those parts of the ring beyond the disc of the planet at either side, which by projection are reduced to the form of the parts of an ellipse near the extremities of its greater axis, -and that the open parts of the ansse are produced by the dark sky visible through the space between the ring and the planet. The improved telescopes, and greatly multiplied number and increased zeal and activity of observers, have supplied much more definite information as to the form, dimensions, structure, and position of this most extraordinary and unexampled appendage, It has been ascertained that it consists of an annular plate of matter, the thickness of which is very inconsiderable compared with the superficies. It is nearly, but not precisely, concentric with the planet, and in the plane of its equator. This is proved by the coincidence of the plane of the ring with the general direction of the belts, and with that of the apparent motion of the spots by which the diurnal rotation of the planet has been ascertained. When telescopes of adequate power are directed to the ring presented under a favourable aspect, dark streaks are seen upon its surface similar to the belts of the planet. One of these having been observed to have a permanence which seemed incom- patible with the admission of the same atmospheric cause as that which has been assigned to the belts, it was conjectured that it arose from a real separation or division of the ring into E2 51 THE PLANETS, ARE THEY INHABITED \ two concentric rings placed one within the other. This conjec- ture was converted . into certainty by the discovery that the same dark streak is seen in the same position on both sides of the ring. It has even been affirmed by some observers that stars have been seen in the space between the rings ; but this requires confirmation. It is, however, considered as proved that the system consists of two concentric rings of unequal breadth, one placed outside the other, without any mutual contact. 5. While the planet is carried round the sun in its orbital motion, the rings are presented to the view of observers situate on the earth under different aspects. In two positions of the planet at opposite points of its orbit the ring is seen edgeways, its plane then passing through the earth. It assumes these positions at intervals of about fifteen terrestrial years, or half a Saturnian year. If the ring were thick enough to be distinctly visible, and if its thickness were uniform, it would at these times have the appearance represented in fig. 1. Fig. 1. As it moves from these positions the rings become inclined at a sensible angle to the visual line, and this angle increasing Fig. 2. from year to year, they appear more and more open, as repre- sented in fig. 2 ; until, after an interval of 7 years, or a quarter THEIR PHASES. of a Saturnian year, the plane of the rings forms the greatest possible angle, about 28, with the visual line. At this time the appearance of the rings would be such as is represented in fig. 3. Fi2. 3. The times at which the rings are presented edgeways to the earth are very nearly identical with those of the Saturnian equinoxes. The last which took place was in 1848, and the next will consequently be in 1863. 6. In 1848, the ring being presented edgeways, some very interesting and curious observations were made upon it by Fijs. 4, 5. M. Julius Schmidt, at the Observatory at Bonn. It was found that the ring, instead of appearing as an even, thin line of light 53 THE PLANETS, ARE THEY INHABITED ? such as is represented in fig. 1, appeared as a broken and uneven line. We have selected from the telescopic drawings made on that occasion by M. Schmidt, four, which are shown in Figs. 4, 5, 6, 7. These are intended only to represent the appearances of the edge of the rings, and not of the streaks on the disk of the planet. Fig. 4 represents the ring as seen on the 26th June. Fig. 5 ,, ,, 3rd Sept. Fig. 6 5th Sept. Fig. 7 llth Sept. 7. This singular appearance must arise from great mountainous inequalities on the surface of the ring, rendering it much thicker at some parts than at others. At some parts it is too thin to be visible at Saturn's distance, while at the parts rendered thicker by lofty mountains, it is apparent. 8. The breadth of the rings, as well as of the intervals which separate them from each other and from the planet, have been submitted to very precise micrometric observations ; and the results obtained by different observers do not differ from each other by a fortieth part of the whole quantity measured. In the 54 DIMENSIONS OF SATURN S RINGS. following table are given the results of the micrometric observa- tions of Professor Struve, reduced to the mean distance. a i 34 ~- -H n r- Miles. p 1* Semi-diameter of the planet . r 8" -995 1-000 39,580 Exterior semi-diameter of exterior ring a, 20-047 2-229 88,209 Interior do. a! 17-644 1-961 77,636 Breadth of exterior ring . a a' 2-403 0-268 10,573 Exterior semi-diameter of interior ring Interior do. do. b V 17-237 13-334 1-916 1-482 75,845 58,669 Breadth of interior ring . bb' 3-903 0-434 17,176 Width of interval between the rings a'b 0-407 0-045 1,791 Width of interval between planet and "1 interior ring . . . . J b' r 4-339 0-482 19,089 Breadth of the double "ring, including] ,. interval }|< 6-713 0-747 29,540 The relative dimensions of the two rings, and of the planet within them, are represented in fig. 8 projected upon the common plane of the rings and the planet's equator. Each division of the subjoined scale represents 5000 miles. 9. The most surprising result of recent telescopic observations of this planet has been the discovery of a ring, composed, as it would appear, of matter reflecting light much more imperfectly than the planet or rings already described ; and, what is still more extraordinary, transparent to such a degree that the body of the planet can be seen through it. In 1838, Dr. Galle, of the Berlin observatory, noticed a phe- nomenon, which he described as a gradual shading off of the inner ring towards the surface of the planet, as if the solid matter of the ring were continued beyond the limit of its illuminated surface, this continuation of the surface being rendered visible by a very feeble illumination, such as would attend a penumbra upon it ; and measures of this obscure surface were published by him in the " Berlin Transactions " of that year. The subject, however, attracted very little attention until towards the close of 1850, when Professor Bond, of Boston, and Mr. Dawes, in England, not only recognised the phenomenon noticed by Dr. Galle, but ascertained its character and features 55 THE PLANETS, ARE THEY INHABITED 1 with great precision. The observations of Professor Bond were not known in England until the 4th of December ; but the phenomenon was very fully and satisfactorily seen and described Ffc. 8. 30 40 by Mr. Dawes, on the 29th oi November. That astronomer, on the 3rd of December, called the attention of Mr. Lassell to it, who also witnessed it on that evening at the observatory of Mr. Dawes ; and both immediately published their observations and descriptions of it, which appeared in Europe simultaneously with those of Professor Bond. It was not, however, until 1852 that the transparency was fully ascertained. From some observations made in September, Mr. Dawes strongly suspected its existence ; and about the same time it was clearly seen at Madras by Captain Jacob, and in October by Mr. Lassell at Malta, whither he had removed his observatory to obtain the advantages of a lower latitude and more serene sky. The result of these observations has been the con- 60 8ATUBN8 OBSCURE EIXG. elusive proof of the unique phenomenon of a semi-transparent annular appendage to this planet. 10. The planet surrounded by this compound system of rings is represented at the head of this chapter. The drawing is reduced from the original sketch, made by Mr. Dawes. The principal division of the bright rings is visible throughout its entire circumference. The black line, supposed to be a division of the outer ring, is visible iu the drawing of Mr. Dawes ; but was not at all seen by Mr. Lassell. A remarkably bright thin line, at the inner edge of the inner bright ring, was distinctly seen by Mr. Dawes in 1851 and 1852. The inner bright ring is always a little brighter than the planet. It is not, however, uniformly bright. Its illumination is most intense at the outer edge, and grows gradually fainter towards the inner edge, where it is so feeble as to render it somewhat difficult to ascertain its exact limit. It would seem as if the imperfectly reflective quality there approaches to that of the obscure ring recently discovered. The open space between the ring and the planet has the same colour as the surrounding sky. 11. The rings must obviously form a most remarkable object in the firmament of Satumian observers, and must play an important part in their uranography. The problem to determine their apparent magnitude, form, and position, in relation to the fixed stars, the sun, and Satumian moons, has, accordingly, more or less engaged the attention of astronomers. It is nevertheless a singular fact that, although the subject has been discussed and examined by various authorities for three quarters of a century, the conclusions at which they have arrived, and the views which have been generally expressed and adopted respecting it, are completely erroneous. 12. In the Berlin Jahrbuch for 1786, Professor Bode published an essay on this subject, which, subject to the imperfect knowledge of the dimensions of the rings which had then resulted from the observations made upon them, does not seem to differ materially in principle from the views adopted by the most eminent astrono- mers of the present day. Sir John Herschel, in his "Outlines of Astronomy," edit. 1849, states that the rings as seen from Saturn appear as vast arches spanning the sky from horizon to horizon, holding an almost invariable situation among the stars ; and that, in the hemisphere of the planet which is on their dark side, a solar eclipse of fifteen years' duration takes place. This statement, which has been reproduced by almost all writers both in England and on the continent, is incorrect in both the particulars stated. First, the rings do not hold an 57 THE PLANETS, ABE THEY INHABITED \ almost invariable position among the stars. On the contrary, their position with relation to the fixed stars is subject to a change so rapid that it must be sensible to Saturnian observers, the stars seen on one side of the rings passing to the other side from hour to hour. Secondly, no such phenomenon as a solar eclipse of fifteen years' duration, or any phenomenon bearing the least analogy to it, can take place on any part of the globe of Saturn. Among the continental astronomers who have recently reviewed this question, the most eminent is Dr. Madler, to whose observations and researches science is so largely indebted for the information we possess respecting the physical character of the surface of the Moon and Mars. This astronomer maintains, like Herschel, that the rings hold a fixed position in the firmament, their edges being projected 011 parallels of declination, and that, consequently, all celestial objects are carried by the diurnal motion in circles parallel to them, so that in the same latitude of Saturn the same stars are always covered by the rings, and the same stars are always seen at the same distance from them. This is also incorrect. The zones of the firmament covered by the rings are not bounded by parallels of declination, but by curves which intersect these parallels at various angles. Dr. Madler enters into elaborate calculations of the solar eclipses which take place during the winter half of the Satur- nian year. He computes the duration of these various eclipses in the different latitudes of Saturn, and gives a table, by which it would appear that the solar eclipses which take place behind the inner ring vary in length from three months to several years, that the duration of the eclipses produced by the outer ring is still greater, and that the duration of the appearance of the sun in the interval between the rings varies in different latitudes from ten days to seven and eight months.* These various conclusions and computations of Bode, Herschel, Madler, and others, and the reasoning on which they are based, are altogether erroneous ; and the solar phenomena which they describe have no correspondence with, nor any resemblance to, the actual uranographical phenomena. 13. The problem of the appearance of the system of rings in the Saturnian firmament, and their effect in occulting and eclipsing occasionally and temporarily the sun, the eight moons, and other celestial objects, was fully discussed, and, for the first time, definitely solved in a memoir by the author of * See Populare Astronomic, von Dr. J. H. Madler. Berlin, 1852. 53 APPEARANCE OF RINGS TO SATUKNIAXS. these pages, read to the Royal Astronomical Society in 1853, and published in the twenty-second volume of their " Transactions." It is there demonstrated that the infinite skill of the Great Architect of the Universe has not permitted that this stupendous annular appendage, the uses of which still remain undiscovered, should be the cause of such darkness and desolation to the inhabitants of the planet, and such an aggravation of the rigours of their fifteen years' winter, as it has been inferred to be from the reasoning of the eminent astronomers already named, as well as many others ; who have either adopted their conclusions, or arrived at like inferences by other arguments. It is shown, on the contrary, that, by the apparent motion of the heavens, produced by the diurnal rotation of Saturn, the celestial objects, including, of course, the sun and the eight moons, are not carried parallel to the edges of the rings, as has been hitherto supposed ; that they are moved so as to pass alter- nately from side to side of each of these edges ; that in general such objects as pass under the rings are only occulted by them for short intervals before and after their meridional culmina- tion; that although under some rare and exceptional circumstances and conditions, certain objects, the sun being among the number, are occulted from rising to setting, the continuance of such phenomenon is not such as has been supposed, and the places of its occurrence are far more limited. In short, it has no such character as would deprive the planet of any essential condition of habitability. Fig. 9 14. The appearance which the ring presents to the Saturnians must vary very much with the latitude of the observer and the season of the year. In the summer half-year, the observer and the sun being on the same side of the ring, it will present the appearance of an arch in the heavens, bearing some resemblance in its form to a rainbow, the surface, however, having an appearance resembling that of the moon. 59 THE PLANETS, ARE THEY INHABITED \ The vertex or highest point of this arch will be upon his meri- dian, and the two portions into which it will be divided by the meridian will be equal and similar, and will descend to the horizon at points equally distant from the meridian. The apparent breadth of this illuminated bow will be greatest upon the meridian, and it will decrease in descending on either side towards the horizon, where it will be least. The division between the two rings will be apparent, and, except at places within a very short distance of the equator, the firmament will be visible through it. The distance of the edge of the bow from the celestial equator will not be everywhere the same, as it has been erroneously assumed to be. That part of the bow which is upon the meridian will be most remote from the celestial equator ; and in descend- ing from the meridian on either side towards the horizon, the decimation of its edge will gradually decrease, so that those points which rest upon the horizon will be nearer to the equator than the other points. 15. Some idea may be formed of the varieties of appearance presented by the ring to observers in different latitudes of the planet, by imagining an observer starting from that Saturnian pole which is on the same side of the ring as the sun, to travel along a meridian towards the equator. At first the convexity of the planet will intercept all view whatever of the ring, and this, as has been shown in the memoir already referred to, will continue until he has descended below the latitude 63 20' 38". At this latitude the ring will just touch his horizon, and will continue to be more and more seen until he descends to latitude 47 33' 51", when both rings will be seen as represented in fig. 9. Fig. 10. In descending to lower latitudes, more and more of the rings will rise above the horizon, and they will assume the form of a double bow, as represented in fig. 10. As the observer descends lower and lower in latitude, the bow 60 APPEARANCE OF RINGS TO SATURXIANS. will take a higher and higher position, and will span a greater portion of the firmament, as represented in figs. 11, 12, 13. It will be observed that, in all cases, the width of the bow decreases from the meridian to the horizon, and also decreases with the latitude of the observer. Fig. 11. Fig. 12. In fig. 14 is represented a portion of the ring, with the satel- lites as they appear above, showing different lunar phases. We must refer those who may desire to pursue the Urano- graphyof Saturn into its details to the*memoir already cited, 61 THE PLANETS, ARE THEY INHABITED \ published in the " Transactions of the Royal Astronomical Society ;" and to Chapter XV. of Dr. Lardner's " Astronomy." 14. 16. We have thus presented the reader with a brief and rapid sketch of the circumstances attending the two chief groups of globes which compose the solar system, and have explained the numerous and striking analogies which, taken together, amount to a demonstration that, in the economy of the material universe, these globes must subserve the same purposes as the earth, and must be the dwellings of tribes of organised creatures, having a corresponding analogy to those which inhabit the earth. 17. The differences of organisation and character which would be suggested as probable or necessary by the different distances of the several planets from the common source of light and heat, and the consequent differences of intensity of these physical agencies upon them, by the different weights of bodies on their surfaces, owing to the different intensities of their attractions on such bodies ; by the different intervals which mark the alter- nations of light and darkness ; are not more than are seen to prevail among the organised tribes, animal and vegetable, which inhabit different regions of the earth. The animals and plants of the tropical zones differ in general from those of the temperate and the polar zones ; and even in the same zone we find different tribes of organised creatures flourish, at different elevations above the level of the sea. There is nothing more wonderful than this in the varieties of organisation suggested by the various physical conditions by which the planets are affected. But these arguments and analogies will acquire great additional force, when it is shown that the other bodies composing the solar system are not furnished with like provisions, and exhibit none of the fitness, for the dwelling-places of such tribes. 18. The Sun, as will be shown in another part of this series, is a vast globe, invested with an ocean, or rather an atmosphere, of flame, in which the most astonishing convulsions and eruptions 62 RECAPITULATION. are continually manifested. Here is no moderated and regulated temperature, no alternations of light and darkness, no succession of seasons, no varieties of climate, no divisions of land and water. The sun is, in fact, a vast globular furnace, the heat emitted from each square foot of which is seven times greater than the heat which issues from a square foot of the fiercest blast furnace. Such is the intensity of this heat, that although the distance of the earth from the sun is little less than 100,000000 of miles, and although the surface of the earth, by reason of its diurnal rotation, is withdrawn from the sun's olirect influence during alternate intervals of twelve hours, yet the total quantity of heat received by the earth from the sun in a year is sufficient, if uni- formly diffused over its surface, to liquefy a crust of ice covering it 100 feet thick ! It follows from this that the average heat received by each square foot of the earth's surface from the sun in a year would be sufficient to dissolve 5400 Ibs. weight of ice. How entirely removed from all analogy with the earth such a globe of fire must be, is apparent. 19. The moon, on the other hand, while it has nothing in common with the sun, is not the less destitute of all those analogies to the earth which suggest habitability. We shall, on another occasion, explain fully the circumstances attending our satellite. For the present, it will be sufficient to observe that it has no atmosphere, no clouds, no water or other liquids, no intervals of light and darkness, bearing any analogy to our days and nights ; that its surface bristles with one unbroken con- tinuity of rugged mountainous region more savage than the glaciers which crown the summits of the Alps, the Andes, or the Cordilleras, and that even in the valleys a temperature must prevail colder than that of our poles. It will therefore be easily imagined how little analogy such a globe has to the earth, and how utterly unsuited it would be for the habitation of organised tribes. 20. Astronomical observation renders it probable that the satellites of the other planets are under physical conditions similar to that of the moon, and that, like the moon, they are deprived of the conditions of habitability. 21. A numerous class of bodies, called comets, have been proved by modern observation to be connected by gravitation with the solar system. These bodies appear generally to be divested of all solidity, and to be masses of vaporous matter floating through the system. It is obvious that these can have no analogy to the earth. In the space between the two groups of planets which present 63 THE PLANETS, AEE THEY INHABITED 1 such striking analogies to the earth, another group consisting of six or seven-and-twenty bodies, circulate round the sun, as represented in the plan of the system given in this tract, Chap. II., fig. 1. The number of these is augmented every year by the discovery of some which were not before seen. 22. These bodies, which have been called PLANETOIDS or ASTEROIDS, obey the law of gravitation in their motion round the sun. Their distances from that luminary are not only different one from another, but they differ from all the other planets in their extremely small magnitude. In the telescope they are seen as stars of the tenth or twelfth magnitude, and their real magnitudes are so minute that they have never yet been certainly ascertained, notwithstanding the number and power of the telescopes that have been directed to them. As to their origin, and the parts they play in the economy of creation, nothing can be offered but the most vague and uncertain conjecture. According to the opinion of some, they are the minute fragments of a single planet, which has been smashed to pieces by collision with the solid nucleus of a comet, assuming the possible existence of such a body. According to others, the fracture may have been produced by internal explosion, arising from causes similar to those which produce earthquakes and volcanic phenomena. Others again reject altogether the hypo- thesis of the fracture of a formerly existing planet, and substitute for it the contrary hypothesis, that these numerous minute bodies are the germs or constituent elements of a future planet, which will be formed by these bodies gradually coalescing into one globe, some of them, perhaps, assuming the character of satellites to it. These are speculations which, however ingenious and attractive, are beside our present purpose. It is plain that the planetoids, as they now actually exist, present none of the analogies to the earth which are so conspicuous in the other planets. WEATHER PROGNOSTICS. 1. Popular errors as to meteorological phenomena 2. Weather almanacks, their absurdities Herschel's Weather Table Murphy's Almanack. 3. Influence of the moon on the weather Toaldo's theory Pilgrim's observations Horsley's observations and papers Schubler's observa- tions and calculations Arago's examination of them Observations of FlaugergiTes and Bouvard. 4. Metonic cycle Arago's examination of it, and observations. 5. Arago's examples of the speculation and reasoning of meteorologists. 6. Changes of the moon have no influence on the weather. 1. THE physical laws -which govern the phenomena of our atmosphere, and regulate the changes of the weather, have always been a favourite topic of speculation. As the principles of astronomical science supplied means of predicting, with the highest possible degree of certainty and precision, the motions and appearances of the heavenly bodies, it was not unnaturally expected that atmospherical phenomena might be brought under equally clear and certain rules. The connection of the lunar motions with the tides was apparent, long before the influence by which the moon produced the rise and fall of the waters of the ocean was explained ; and this gave countenance, at a very early period, to the idea that that body had an influence on the atmosphere, if not as certain and regular as on the waters, still MUSEUM, No. 2. F 65 WEATHER PROGNOSTICS. sufficiently so to furnish probable grounds for conjecture as to certain changes of the weather. But even before analogies of this kind could have furnished much ground for reasoning, and when the heavenly bodies must have been regarded more as signs than causes, meteorological phenomena were connected with them by popular observation. The influence of climate on all the interests of a people in a pastoral, and subsequently in an agricultural state, is obvious ; and accordingly we find weather prognostics coming down by tradition from the most remote antiquity. By a course, however, contrary to most other subjects of observation and inquiry, this was corrupted rather than improved with the progress of knowledge and civilisation ; and what was once a mere system of signs of a certain present state of the atmosphere, indicating certain approaching changes, was, by the craving oi philosophy after the relations of cause and effect, converted into the most absurd system of rules, having no foundation in nature, never fulfilled by the phenomena except fortuitously, and maintaining their ascendancy by the unbounded credulity of mankind. The truth is, that the ancient prognostics, whether derived from the moon, from the sun, or from the stars, were, in the first instance, used legitimately as mere indications of the state of the atmosphere by persons too simple-minded and uneducated to trouble themselves much with the philosophy of cause and effect ; but when these appearances came into the hands of philosophers, they were at once elevated to the rank of physical causes, and their dominion extended in proportion to the dignity and importance thus conferred upon them. Such notions were in keeping with a philosophy which made the moon the boundary between corruption, change, and passiveness, on the one hand, and the active powers of nature on the other. "Thus," says Horsley, "the uncertain conclusions of an ill-conducted analogy, and false metaphysics, were mixed with a few simple precepts, derived from observation, which probably made the whole of the science of prognostication in its earliest and purest state." Although from age to age the particular circumstances and appearances connected with the moon, by which the atmospheric vicissitudes were prognosticated, were changed, still the faith of mankind in general in her influence on the weather has never been shaken ; and even in the present day, when knowledge is so widely diffused, and physical science brought, as it were, to the doors of all who have the slightest pretension to education, this belief is almost universal. Many, it is true, may discard 66 WEATHER ALMANACKS. predictions which affect to define, from day to day, the state of the weather. There are few, however, who do not look for a change of the weather with a change of the moon. It is a belief nearly universal, that the epochs of a new and full moon are in the great majority of instances attended by a change of weather, and that the quarters, though not so certain, are still epochs when a change may be probably expected. Those who have least faith in the meteorological influence of the moon, extend their belief thus far. It is worthy of remark, that this persuasion of the meteoro- logical influence of the moon is never so strong and so undoubting as among those classes of persons who are at once most deeply interested to foreknow the weather, and have the best and most unc easing opportunities of observing the phenomena. No navigator, from the captain or master to the commonest seaman, no agriculturist or gardener, from the largest farmer to the com- monest field-labourer, ever doubts for a single moment the influence of new and full moon on fair weather and foul. Notwithstanding the general diffusion of scientific information and the multitude of encyclopaedic compilations and elementary and popular digests of physical science that are accessible, it is astonishing how universal is the ignorance on this subject even among persons who might be supposed to spare no pains to inform themselves. Thus we find in the otherwise excellent compilations of the late Mr. Loudon on Agriculture and Gar- dening, a chapter on the means of prognosticating the weather, in which the supposed influences of the lunar phases have precedence over the indications of the barometer, the ther- mometer, the hydrometer, and the rain-gauge, the former being characterised by the author as "natural," and the latter as "artificial" data. Why the variations of the atmospheric pres- sure and temperature, and the quantities of water which are suspended in, or which fall from the atmosphere, should be regarded as less " natural " indications of the weather than the moon, the author does not inform us. We find, however, in these popular works of reference, the lunar prognostics reproduced in their minutest details, and the fantastical theories of Toaldo, Lambert, and Cotte, referred to as though they were as sound as that of gravitation. 2. In some one of the numerous weather almanacks which have from time to time circulated, there appeared a table pro- fessing to indicate the relation between the changes of the weather and the lunar phases, entitled "Herschel's Weather Table." The general public have fallen into a natural and excusable mistake (from which Mr. London does not seem to F2 67 WEATHER PROGNOSTICS. have escaped), in supposing that this absurd affair has been sanctioned by the authority of one of the illustrious astronomers whose name it bears. Whether the table in question is really the production of any person bearing that celebrated name we cannot say ; but the public may be assured that neither of the eminent astronomers who have rendered the name of Herschel for ever memorable, has had any concern with it. It is astonishing, in this age of the diffusion of knowledge, how susceptible the public mind is of excitement on any topic, the principles of which do not lie absolutely on the surface of the most ordinary course of elementary education. It was only in the year 1832 that a general alarm spread throughout France, lest Biela's comet in its progress through the solar system, should strike the earth ; and the authorities in that country, with a view to tranquillise the public, induced M. Arago, the astronomer royal, to publish an essay on comets, written in a familiar and intelligible style, to show the impossibility of such an event. Several panics in England, connected with physical questions, have occurred within our memory. There prevailed in London a " water panic," during which the public was persuaded that the water supplied to the metropolis was destructive to health and life. While this lasted, the papers teemed with announce- ments of patent filtering machines ; solar-microscope makers displayed to the terrified Londoners troops of thousand-legged animals disporting in their daily beverage ; publishers were busy with popular treatises on entomology ; and the public was seized with a general hydrophobia. It was in vain that Brande ana- lysed the water at the Eoyal Institution, and Faraday attempted to reason London into its senses. Knowledge ceased to be power ; philosophy lost its authority. Time was, however, more efficacious than science ; and the paroxysms of the disease having passed through their appointed phases, the people were convalescent. There was at another time a panic against atmo- spheric air, during which the inhabitants of the great metropolis (in a literal sense) scarcely dared to breathe. The combustion of coal was denounced as the great evil in this case. Calcula- tions were circulated of the number of cubic feet of sulphurous gas taken into the lungs of each adult inhabitant per annum ; the properties of carbonic acid were discussed behind counters ; patent furnaces were plentifully invented and advertised for sale ; and parliament was urged to pass a bill for the purifi- cation of the atmosphere, and to compel all who used fires to consume their own smoke. In 1838, the English public, who are especially excitable, were 68 INFLUENCE OF THE MOON. seized with a rage for weather prognostics, produced apparently by an unusually rigorous and long-continued frost, which took place in the months of January and February. In one of the numerous " weather almanacks " which were then circulated, a fortuitous coincidence occurred, by which it appeared that the coldest day had been predicted by the author, an adroit Hibernian named Patrick Murphy. The conductors of some of the leading journals, without waiting to obtain better information from any of the acknowledged scientific authorities, gravely descanted on the "great advantages which would accrue to the farmer, the manufacturer, the navigator, and others, from the certain pre- diction of the weather from week to week and from day to day," and admitted that they looked forward to the period not far distant, when " Careful observers might foretel the hour By sure prognostics when to dread a shower." So extreme was the public excitement at the moment on this subject, that the book in which the so-called weather table was published was actually purchased, though its price was high, by the hundred thousand ! So urgent was the demand for it, and so irrepressible the public impatience, that the shop of the publisher, like that of a baker in a famine, was obliged to be protected by the police, who, to keep the thorough- fare unobstructed, marshalled the expectant purchasers in a queue which extended to an incredible length. Yet will it be believed, that when this weather almanack was afterwards examined and compared with the actual changes of the weather by the author of these pages, its pretended predictions were found to fail in seventeen cases out of twenty-four ! 3. Tbe imputed influence of the moon upon the weather may he considered either as a question of theory or a question of fact. Let us consider for a moment the theoretical question. If the moon act upon our atmosphere by attraction, as she acts upon the waters of the ocean, she will produce atmospheric tides. The greater mobility of air will cause those tides to be formed more rapidly than the water tides; and it may be, perhaps, assumed that they will always be placed, either exactly, or very nearly under the moon. Thus, as there is high water twice daily, so would there be high air twice daily ; and the times of this air-tide would correspond with the moments of the transit of the moon over the meridian above and be'ow the horizon. WEATHER PROGNOSTICS. The same causes, also, which at new and full moon produce spring tides, and at the quarters neap tides, would produce spring and neap atmospheric tides at the same epochs. At new and full moon, therefore, the air ought to be higher, daily, at noon and midnight than at any other times during the month ; and, on the other hand, at quarters it ought to be lower. If, then, the barometer be observed twice daily, viz., at the times of the moon's transit over the meridian, above and below the horizon, it ought (so far as it will be affected by the sun and moon) to be the highest at new and full moon, and lowest at the quarters. Now as the rise of the barometer generally indi- cates fair weather, and its fall foul weather, the conclusion to which this would lead would be, that the epochs of new and full moon should be generally fair, while at the quarters bad weather would generally prevail. This, however, is not the popular opinion. The traditional maxim is that a change may be looked for at new and full moon ; that is, if the weather be previously fair, it will become foul ; if previously foul, fair. M. Arago submitted to rigorous investigations a series of barometric observations made in relation to the lunar phases at the Paris Observatory, and continued for twelve years, and found that the effect of the lunar attraction on the barometer at the epochs of the high and low atmospheric tides could not have exceeded the l-600th of an inch, a quantity such as could produce no conceivable effect upon the weather. It is evident, then, that if the moon have any influence on our atmosphere, it cannot proceed from any cause analogous to that which produces the tides of the ocean. But it may be said that although the moon may not affect the atmosphere by her gravitation, yet she may influence it by her light, or by electrical or magnetical emanations, or, in fine, by some occult physical causes not yet discovered by astronomers. This is an objection that, from its vagueness and indenniteness, is difficult to be rebutted by any means which theory can furnish. It is known that the light of the moon concentrated in a point by the most powerful burning lenses, is incapable of producing the slightest sensible effect on the most susceptible thermometer. Neither is it found to produce any effects of an electrical or magnetical kind. It may be assumed generally, that the effects commonly imputed to the moon, in producing change of weather at her principal phases, are so contradictory, that it is impossible to imagine any physical causes which could account for them. If the new and full moon and the quarters are attended by changes of the weather, the cause producing this effect, 70 INFLUENCE OF THE MOON. under the same circumstances, must have incompatible influences ; if fair weather precede the phase, the supposed physical cause must be such as to be capable of converting it into foul weather ; and if foul weather precede the phase, the same cause must convert it into fair weather. It will be admitted that it is hard to imagine any physical agent whatever, which under precisely the same circumstances, shall produce upon the same body effects so opposite. But let us dismiss the theoretical view of the question, and inquire as to the facts. Has it been found, as a matter of fact, that the epochs which mark the principal phases of the moon have been, in the majority of cases, attended with a change of weather ? Before this question can be satisfactorily answered, it will be indispensable that the meaning of the phrase, change of weather, be distinctly understood. An observer who is pre- disposed to a belief in the influence of the lunar phases, will consider himself warranted in classing as a change of weather every transition from a calm to a wind, whether feeble or forcible every change from a clear and serene firmament to one ever so little clouded from a firmament a little clouded to one quite covered over. He will consider the change from a day absolutely free from rain to one in which a few drops may chance to fall, as well entitled to be recorded as a change of weather as if the transition had been from a day absolutely fair to one of incessant rain. On the other hand, a disbeliever in the lunar influences will class all very slight changes as settled weather, and will only register as changes those of a very decisive character. These are difficulties hard to remove, but unless they be removed, how is it possible to compare together, with any probability of arriving at the truth, the records of different observers ? What value or importance are we to attach to the results of any such observations, unless the prejudices of the observer are admitted into our estimate ? Toaldo has given the result of a comparison of observations continued for forty-five vears at Padua, in which changes of weather are recorded in juxta-position with the lunar phases. Without detailing the particulars of these calculations, we may state at once the following results of them. He found that for every seven new moons the weather changed at six, and was settled only at one ; for every six full moons, the weather changed at five, and was settled at one ; for every three epochs of the quarters, there were two changes of weather. He also examined the state of the weather in reference to the moon's distance from the earth, which is subject to some variation. The position of the moon when most distant from 71 WEATHER PROGNOSTICS. the earth is called apogee, and her position when nearest is called perigee. He found that of every six passages of the moon through perigee there were five changes of weather ; and of every five through apogee there were four changes of weather. It is clear that if these results would bear the test of rigid examination, they would be decisive in favour of the popular notion of the lunar influence. But let us see in what manner Toaldo con- ducted his inquiry. He was himself an avowed believer in the lunar influence, not merely upon the atmosphere, but even on the state of organised matter. In his memoir he has not informed us what atmo- spherical changes he has taken as changes of weather ; and it is fair to presume that the bias of his mind would lead him to class the slightest vicissitudes under this head. But, further, Toaldo, in recording the changes of weather coinciding with the epochs of the phases, did not confine himself to changes which took place upon the particular day of the phase. On the pretext that time must be allowed for the physical cause to produce its effect, he took the results of several days. At the new and full moon he included in his enumeration all changes which took place two or three days before or two or three days after the day of new or full moon ; while for the quarters he only included the day preceding and the day following the phases ; and for epochs not coincident with the lunar phases, he only counted the changes of weather which took place on the particular day in question. It appears, then, that by the changes coinciding with a new and full moon recorded by Toaldo are understood any changes occurring within the space of from four to six days ; for the changes recorded at the quarters are to be understood those which occurred within the space of three days ; and for those not coinciding with the phases the changes which occurred on a single day. It will not, we presume, require much mathematical sagacity to perceive that the results of such an inquiry must have been just what Toaldo found them to be ; and that, if instead of taking the epochs of the lunar phases, he had taken any other periods whatsoever, anil tried them by the same test, he would have arrived at the same results. Five days at the new and full moon would include a third of the entire lunar month; and thus a third of all the changes of weather which occurred in that period were ascribed by Toaldo to the lunar influence. Professor Pilgrim has examined a series of observations on the lunar phases as connected with the changes of weather, made at Vienna, and continued from 1763 to 1787 a period of twenty- five years and he has found that, of every hundred cases of the 72 PILGRIM, TOALDO, AND HORSLEY. phases, the proportion of the occurrence of changes to that of the settled state of the weather was as follows : Changes. Settled Weather. New moon .... 58 42 Full moon . . . 63 Quarter . . . .63 Perigee . . . 72 Apogee . . . .64 New moon at perigee . . 80 New moon at apogee . .64 Full moon at perigee . . 81 Full moon at apogee . .68 37 37 28 36 20 36 19 32 Admitting these results, it would follow, contrary to popular belief and to the observations of Toaldo, that the new moon is the least active of the phases ; and that the full moon and quarters are equally active ; also that the influence of perigee, or the nearest position of the moon, is greater than that of any of the phases, while the influence of apogee, or its greatest distance, is equal to that of the quarters and full moon, and greater than that of the new moon. But Pilgrim's calculations are liable to objections similar to those to which Toaldo's are obnoxious. Like Toaldo, he included in his enumerations of changes corresponding to the phases, changes which occurred the days preceding and following the phases : this being the case, the only wonder is that the proportion which he has found, especially for the new moon, is not more favourable to his hypothesis. But independently of this, Pilgrim's results are not entitled to any confidence : they bear internal evidence of their inaccuracy ; and besides, the observations were not continued for a sufficient length of time to give a safe and certain conclusion. In the years 1774 and 1775, Dr. Horsley directed his attention to the question, aud published two papers in the " Philosophical Transactions," with a view to dispel the popular prejudice on the subject of lunar influences. Horsley's observations, however, were confined to so short a period of time (two years), that they could not be expected to afford any satisfactory results. He found that in the year 1774 there were only two changes of weather which corresponded with the new moon, and none with the full moon ; and that in the year 1775 there were only four changes which corresponded with the new moon, and three with the full moon. Dismissing, then, this popular notion of the correspondence of changes of the weather with the lunar phases, let us consider the question of lunar influences in a more general point of view, 73 WEATHER PROGNOSTICS. and see whether observation has supplied any ground for the supposition of any relation whatever of periodicity between the moon and the weather. M. Schiibler examined this question with considerable care so recently as 1830, and published the results of his observations, which, shortly after, were re-examined by M. Arago. Schiibler's calculations were founded on meteorological observa- tions made at Munich, Stutgard, and Augsburg, for twenty-eight years.* His object was to ascertain whether any correspondence existed between the lunar phases and the quantity of rain which fell in different parts of the month. He denned a rainy day to be one in which a fall of rain or snow was recorded in the meteorological journals, provided it affected the rain-gauge to an extent exceeding the six-hundredth part of an inch. So far as his observations may be relied upon, it would follow, that in the places where they were made, out of 10,000 rainy days the following are the number of those days which would happen at the different lunar phases. Newmeon .... 306 First octant. . . . . . 306 First quarter . . . .325 Second octant . . . . 341 Full moon .... 337 Third octant . . . . 313 Last quarter .... 284 Fourth octant . . . . 290 Now, as there are twenty-nine days and a half in the lunar month, if we suppose the fall of rain to be distributed equally through every part of the month, the total number of these 10,000 days which should happen on the eight days of the phases, would be found by a simple proportion ; since it would bear to 10,000 the same proportion that 8 bears to 29^: the number would therefore be 27'12. Whereas, it appears from the above table, that the actual number which fell upon these days were 25*02 : it appears, therefore, that less than the proportional amount occurred upon them. Pilgrim had already, in 1788, attempted to ascertain the influence of the hinar phases on the fall of rain ; and he found that in every hundred cases there were 29 days of rain on the full moon, 26 at the new moon, and 25 at the quarters. The preceding observations refer only to the number of wet days. Schiibler, however, also directed his inquiries to the * At Munich, from 1781 to 1788 inclusive : at Stutgard, from 1809 to 1812 inclusive ; and at Augsburg, from 1813 to 1828 inclusive. 74 MOON AND WEATHER COMPARED. influence of the lunar phases on the quantity of rain and on the clearness of the atmosphere. From observations continued for sixteen years at Augsburg, including 199 lunations, he obtained the following results : Epochs. Number of clear days in 16 years. Number of overcast days in 16 years. Quantity of rain in 16 years in inches. New Moon . 31 61 26-551 First quarter Second octant 38 25 57 65 24-597 26-728 Full moon . 26 61 24-686 Last quarter 41 53 19-536 In this table, by a clear day, is meant suck days as exhibited a cloudless sky at seven in the morning, and at two and nine o'clock in the afternoon ; those that were not clear at these hours, were counted as cloudy days. These results are in accordance with the former. It appears that the number of clear days is more frequent in the last quarter, which is an epoch at which, by the former method of inquiry, the number of rainy days was least ; also the number of cloudy days is greatest at the second octant, which is a period at which the number of rainy days are found to be greatest ; the depth of rain also agrees with this, being the greatest about the second octant, and least at the last quarter. Schiibler extended his inquiries to the influence of the moon's distance on rain ; and he found that, on examining 371 passages of the moon through the positions of her extreme limits of distance, during the seven days nearest to perigee it rained 1,169 times ; and during the seven days nearest apogee it rained 1,096 times. Thus, cceteris paribits, the nearer is the moon to the earth the greater would be the chances for rain. From all that has been stated, it can scarcely be denied that there exists some correspondence between the prevalence of rain and the phases of the moon. What that exact correspondence is, remains for more extended and accurate observations to inform us ; but meanwhile it may be safely affirmed that it is not such as to constitute a prognostic in any sense approaching to that in which it has been popularly adopted. That some extremely small excess of rain falls during the four days which precede the day of full moon, and a correspondingly small defect during the four days which precede the day of new moon, seems to be to a certain degree probable. But this pluvial variation is so minute in its amount, even supposing it real and general, as to be utterly imperceptible by any means of popular observation, and therefore practically inapplicable as a prognostic. 75 WEATHER PROGNOSTICS. Schiibler also examined the question of a correspondence between the direction of the wind and the lunar phases, and found that winds from the south and south-west became more and more frequent at those periods of the month at which rain was also observed to increase ; and that such winds were more and more rare, while winds in the contrary direction occurred oftener, towards those epochs of the month when least rain was observed to prevail. These results, it will be seen, are quite in accordance j and the question respecting the mode of action by which the periods of rain are produced, would be reduced to the question of the physical action by which the moon affects the currents of the atmosphere. The connection of barometric indications with atmospheric phenomena is so obvious, that the inquiry as to a correspondence between the lunar phases and the variations of the barometer, could scarcely escape the attention of meteorologists. /M.. Flau- gergue*s accordingly made a series of observations at Viviers (in the department of Arde"che), in France, which were continued from 1808 to 1828, a period of twenty years, on the heights of the barometer in relation to the lunar phases : that the influence of the sun might be always the same, the observations were made at noon, and the heights of the barometer were reduced to what they would be at the temperature of melting ice. The following are the mean heights of the barometer, deduced from these observations : New moon First octant First quarter Second octant Full moon Third octant Last quarter Fourth octant 29743 29761 29740 29-716 29-736 29-751 29-772 29-744 Hence it appears that the height of the barometer is least about four days before full moon, and greatest six or seven before new moon. Now these are about the times at which the investi- gations of Schiibler give the greatest and least quantity of rain : and, since the fall of the barometer generally indicates a tendency to rain, these results are in accordance. Although it must be admitted that the variation of the barometer is in this case so minute, that a sensible effect could hardly be expected from it, still, though minute, it is quite distinct and decided. M. Flaugergues also observed the mean height of the baro- meter when the moon was at her greatest and least distance 76 MOON AND BAROMETER. from the earth, and found that at perigee it was 29713, and at apogee 29- 753. So far, therefore, as this small difference can be supposed to indicate anything, it would indicate a prevalence to rain at perigee and at apogee, which is in accordance with the observa- tions of Schiibler. We have shown that the theory of the moon's attraction, applied to explain atmospheric tides similar to those of the ocean, would lead to the conclusion that the height of the baro- meter observed at noon, when the moon is in her quarters, would be less than its height at noon at new and full moon. Observa- tion, however, shows the very reverse as a matter of fact. The observation of M. Flaugergu6s gives the mean height of the barometer at quadratures 29*756, and at new and full moon 29739 ; the height at quadratures being in excess to the amount of 0'017. This result has been further confirmed by the more recent observations of M. Bouvard, at the Paris Observatory ; he has found the mean height of the barometer at the quarters 29786, and at new and full moon 29759 ; the excess at the quarters being 0'027. 4. Although, therefore, it cannot be denied that there exists a certain relation between the barometric column and the lunar phases, yet it is not the relation which the theory of atmospheric tides would indicate ; and by whatever physical influence the effect may be produced, it is certainly not the gravitation of the moon affecting our atmosphere in a manner analogous to that by which she affects the waters of the ocean. Any physical effects which depend on the relative positions of the sun and moon, as seen from the earth, would necessarily occur in the same order throughout the year, when these two luminaries themselves have corresponding positions in the heavens on the same days of the year. At a very early period in the history of astronomical discovery, it was known that, after the lapse of nineteen years, the sun and moon assume on successive days of the year relative positions. Thus, for example, if the moon were 90 behind the sun on a certain day of a certain month in the year 1800, it would be 90 behind the sun on the same day of the same month in the year 1819, and again in the year 1838, and so on ; but on the same day of the same month in any intermediate year it would have a different relative position with respect to the sun. This cycle of nineteen years was known to the Greeks, and was called the Metonic cycle, from Meton, its reputed discoverer ; and it has always been used as a convenient method of calculating eclipses and other phenomena depending on the relative positions of the 77 WEATHER PROGNOSTICS. sun and moon. In a solar eclipse, the sun and moon must occupy nearly the same position in the heavens ; and in a lunar eclipse, nearly opposite positions : it is evident, therefore, that if an eclipse occur on any day in any given year, an eclipse of the same kind must occur on the corresponding day in every nine- teenth succeeding year. The tides, depending as they do on the relative positions of the sun and moon, would be calculated with facility by means of the same cycle ; and meteorologists who hold the doctrine that atmospheric vicissitudes depend solely or chiefly upon the relative aspects of the sun and moon, have favoured the doctrines, that there is a general cycle of weather, the period of which corresponds with that which we have noticed. Thus they hold, that the general changes of weather succeed each other in the same, or almost the same order, throughout every successive period of nineteen years. We shall not here object, on theoretical grounds, to the doctrine that the true amount of the Metonic cycle is not precisely nineteen years. But it is subject to a stronger objection, founded on the principles which its supporters them- selves rely upon. The attraction of bodies in virtue of their gravitation increases in the same proportion as the square of the distance diminishes ; and as we have already stated that the moon's distance from the earth is variable to an extent not inconsiderable, it is evident that her influence on the atmosphere ought to be expected to depend much more on that variation of distance, than on her relative position with respect to the sun. Now, although the cycle of nineteen years corresponds with the changes of her relative position to the sun as seen from the earth, yet it has no correspondence whatever with the variation of her distance ; and although, on each day of each succeeding period of nineteen years, she will have the same apparent position relatively to the sun, she will not have the same distance from the earth, and, therefore, will not exert the same attraction on our atmosphere. M. Arago (to whom we are indebted for the most complete investigation of this question, and for the collection of the labours of others upon it) has successfully shown that observation affords no countenance or confirmation whatever to this hypothesis. The variation of the moon's distances from the earth (to which we have more than once adverted) is occasioned by the fact that her path round the earth is not circular, but oval the position of the earth being nearer to the one end than the other. As the moon, therefore, approaches the furthermost extremity of her oval orbit, her distance from the earth continually increases until, arriving at that point, it becomes greatest ; as she moves from 78 LUNAR CYCLES. that extremity of the orbit to the other end of the oval, her distance continually diminishes until arriving at the other end, it becomes least. These variations of distance are produced every revolution of the moon round the earth. Now, owing to a certain change of position, to which the moon's orbit is subject, the points which mark her greatest and least distances are subject to a slow, gradual, and regular change ; so that the points in the heavens at which she reaches her greatest and least distances are different every revolution. After the lapse, how- ever, of eight years and ten months, these points having traversed the whole circumference of the heavens, resume their former position very nearly ; so that the actual times at which the moon is observed at the same distances from the earth, and also at the same points in the heavens, recur in a cycle, the length of which is about eight years and ten months. So far, therefore, as the vicissitudes of the weather can be supposed to be influenced by this cause, their period should be such that, after the lapse of nine years, the corresponding states of the weather would be as it were, two months in advance : thus the effect produced in December, 1800, would again be produced in October, 1809, in August, 1818, and so on. If the purpose be to determine the cycle in which the lunar influence so far as it depends on distance, would produce the same effects upon the same days of the year, the duration of the cycle would be six times eight years and ten months : for in six successive intervals of that period, there are exactly fifty-three years ; but any less number of periods of eight years and ten months do not make a complete number of years. Therefore after a cycle of fifty-three years, the moon being on the same day of each successive year at the same distance from the earth, her influence, so far as depends on distances, will be the same, and will produce the same effect upon the weather. 5. Now we cannot better illustrate the loose and inaccurate manner in which scientific principles are applied by some meteorologists than by stating that this cycle of eight years and ten months has formed the theoretical grounds for a reputed meteorological period of nine years. It has been maintained that, through every successive interval of nine years, the changes of weather have a general correspondence : thus, if the state of the weather throughout the year 1800 be examined, it has been said to correspond with the weather throughout the years 1809, and 1818, &c. 6. From all that has been stated, it follows, then, that the popular notions concerning the influence of the lunar phases on the weather have no foundation in theory, and no 79 WEATHER PROGNOSTICS. correspondence with observed facts. That the moon, by her gravitation, exerts an attraction on our atmosphere cannot be doubted ; but the effects which that attraction would produce upon the weather are not in accordance with observed phe- nomena ; and, therefore, these effects are either too small in amount to be appreciable in the actual state of meteorological instruments, or they are obliterated by other more powerful causes, from which hitherto they have not been eliminated. It appears, however, by some series of observations, not yet con- firmed or continued through a sufficient period of time, that a slight correspondence may be discovered between the periods of rain and the phases of the moon, indicating a very feeble influence, depending on the relative position of that luminary to the sun, but having no discoverable relation to the lunar attrac- tion. This is not without interest as a subject of scientific inquiry, and is entitled to the attention of meteorologists ; but its influence is so feeble that it is altogether destitute of popular interest as a weather prognostic. It may, therefore, be stated that as far as observation combined with theory has afforded any means of knowledge, there are no grounds for the prognostications of weather erroneously supposed to be derived from the influence of the sun and moon. Those who are impressed with the feeling that an opinion so universally entertained even in countries remote from each other, as that which presumes an influence of the moon over the weather, must have some foundation, will do well to remember that against that opinion we have not here opposed mere theory. Nay, we have abandoned for the occasion the support that science might afford, and the light it might shed on the negative of this question, and have dealt with it as a mere question of fact. It matters little, so far as this question is concerned, in what manner the moon and sun may produce an effect on the weather, nor even whether they be active causes in producing such effects at all. The point, and the only point of importance is, whether regarded as a mere matter of fact, any such correspondence between the changes of the moon and those of the weather exists as is popularly supposed ? And a short examination of the recorded facts proves that IT DOES NOT. SO I POPULAR FALLACIES. 1. Fallacy of the evidence of the senses. 2. Fallacies of vision. 3. As- applied to the sun and moon. 4. Mechanism of the eye its uses. 5. Perceptions of colour 6. Fallacies of smell, taste, and touch. 7. Fallacies as to number 8. Impressions retained by the eye. 9. Fallacies as to distance 10. Fallacies of touch of apparent tem- perature. 11. Explained by reference to temperature of the human body. 12. Cause of apparent coldness of glass and porcelain. 13. Explanations of the feats of mountebanks exposing their bodies to a fierce temperature. 1. NOTHING can be more common or frequent than to appeal to the evidence of the senses as the most unerring test of physical effects. It is by the organs of sense, and by these alone that we can acquire any knowledge of the qualities of external objects, and of their mutual effects when brought to act one upon* another, whether mechanically, physically, or chemically, and it. might, therefore, not unreasonably be supposed, that what is called the evidence of the senses must be admitted to be conclu- sive as to all the phenomena developed by such reciprocal- action. Nevertheless, the fallacies are numberless into which those are led who take what they consider the immediate results of sen- sible impressions, without submitting them to the severe control and disciplined analysis of the understanding. MUSEUM, No. 4. a 81 POPULAR FALLACIES. These fallacies arise partly from mistaking tlie true character and functions of the organs of sense. These organs were never designed by their Maker to be the instruments of scientific inquiry. If they had been so constructed, they would most pro- bably have been unfit for the ordinary purposes of life. It is observed somewhere, by Locke, we believe, that an eye adapted to perceive the constituent atoms of the metal which forms the hands of a clock might be, from the very nature of its structure, incapable of informing its owner of the hour of the day indicated by the same hands ; and it may be added, that a pair of telescopic eyes, which would discover the population of a distant planet, would ill requite the observer for the loss of that ruder power ot vision necessary to guide his stops through the city he inhabits, and to recognise the friends which surround him. The com- parison of instruments adapted for the use of commerce and domestic economy, and those designed for domestic purposes, furnishes a not less appropriate illustration of the same fact. The highly delicate balance used by the philosopher in his inquiries respecting the relative weights and proportions of the constituent elements of bodies, would, by reason of its very perfection and sensibility, be utterly useless in the hands of the merchant or the housewife. Each class of instruments, has, however, its peculiar uses ; and is adapted to give indications with that degree of accuracy which is necessary and sufficient for the purpose to which it is applied. 2. Of all the organs, that which would seem to be most exact -and unerring in its indications is the eye ; and, although in a certain sense this is true, yet there are no impressions which more imperiously require the exercise of the judgment to adjust and rectify them than those of vision. By this sense we receive the perception, subject, however, to many qualifying conditions, -of form, magnitude, brightness, and colour. There is not one of these qualities, however, which is not frequently mistaken or wrongly estimated. 3. Every one, for example, is familiar with the appearance of the sun and moon when rising and setting. The apparently large orb which they present to the senses is an object of familiar notice. Is not every one impressed with a conviction that the apparent magnitude of the sun when it rises, glowing with a redness acquired from the depth of air through which its rays then pass, is much greater than the apparent magnitude of the same object at noonday 1 and is not the same impression admitted with respect to the rising or setting full moon, com- pared with the same object seen on the meridian ? Yet nothing is more easy than to prove, as a matter of fact, that these 82 FALLACIES OF VISIOX. impressions are fallacious. Let any one adopt any convenient method which may occur to him, to measure the apparent mag- nitude of the sun on the horizon, and again on the meridian, and he will find them the same. This may be accomplished by extending two threads of tine silk parallel to each other in a frame, and placing them in such a position, and at such a distance from the eye, that when presented to the sun or moon, on the horizon, they will, exactly, touch its upper and lower limb, so that their apparent distance asunder will be equal to the apparent diameter of the lunar or solar disk. If this arrange- ment be preserved, and the sun or moon be viewed in the same manner when at, or near, the meridian, it will be found that the threads will equally touch its upper and lower limbs, and that their interval will still measure its apparent diameter. It will, therefore, be evident that whatever be the cause of the illusion, the apparent magnitude of the sun or moon is not greater at rising or setting than in the meridian. Whence, then, it may be asked, arises an impression so universally enter- tained 1 The explanation of this singular effect, in which all astronomers appear to concur, refers it to mental, and not optical causes ; strictly speaking, it is not an optical illusion. The error is one of the mind and not one of the senses. The estimate which we form of the actual magnitude of any visible object depends on a comparison of the apparent magnitude which that object presents to the eye, with the distance at which ~we imagine it to be. Thus if there be two objects buildings, for example, which have to the eye the same apparent height, but which we know or believe to be at different distances from us, we instinc- tively, and without any operation of the judgment of which we are conscious, conceive that which is more distant to be the largest. To apply this reasoning to the case of the sun or moon, we are to consider that when either of these objects is in the horizon, a portion, at least, of the space between the eye and it is occupied by a series of objects with the magnitudes and relative positions of which we are familiar. We are, therefore enabled to make some estimate of a portion of the space that intervenes between the eye and the object. But when the object is in a more elevated position in the firmament, no part of the intervening distance is thus spaced out, and we are accus- tomed to consider the object nearer to the eye. Conceding this, then, it will be asked how it explains the universal impression of the enormously large disk of the sun or moon when rising or setting ; the answer is, that when in or G 2 83 POPULAR FALLACIES. near the horizon the mind is impressed with the idea that the distance of these objects is much greater than when on the meridian, and that their apparent magnitude being the same,, the real magnitude is judged to be greater in the same propor- tion as the distance is supposed to be greater. Thus, if we are impressed with the notion that the sun seen in the horizon i^:- twice as distant as the sun seen in the meridian, we shall infer its diameter to be twice as great, since it appears the same ; and if its diameter is twice as great, its apparent superficial magnitude will be four times as great. The operations of the judgment in such cases are so rapid, and the effect of habit is such, that we are altogether uncon- scious of them. A thousand examples might be given of bodily actions and motions performed by the dictates of the will, of which we retain no consciousness. It is difficult in the case we have just explained, for minds unaccustomed to metaphysical) inquiries, to satisfy themselves of the validity of the explanations we have given. Yet, if it be remembered that it is capable of unequivocal proof that the illusion is not optical, and that, in fact the apparent magnitudes of the moon on the horizon and the meridian are not different, it will easily follow that the erro* must be mental, and the only explanation which has ever beer-, given of it is that which we have here offered. There is perhaps no sense which more requires the vigilant exercise of the understanding to rectify its impressions, thai* that of sight. The susceptibility of the organ of vision itself IF liable to frequent and rapid change, and the same objects at different times produce upon it extremely different impressions, A situation in which, in one condition of the eye, we shalS appear to be in absolute darkness, will present to us, in another state of the organ, sufficient light to render visible the objects around us. If we are suddenly deprived of the illumination 6? any strong artificial light, we appear to be for the moment in absolute darkness ; but when the organ of vision has had time to recover itself, we often find that there is sufficient light to guide us. " Thus when the lamp that lighted The traveller at first goes out, He feels awhile benighted, And lingers on in fear and doubt. "But soon, the prospect clearing, In cloudless starlight on he treads, And finds no lamp so cheering As that light which heaven sheds." MOOHE. 4. The mechanism which the all-wise Creator that made the eyf 84 PERCEPTION OE COLOUR. ?ras contrived to meet these contingencies is marked by the same perfection that prevails through all His works. The opening in the front of the eye, called the pupil, through which light is -admitted to produce vision, is surrounded by an elastic ring, called the iris, which is capable of being contracted or enlarged by the action of certain muscles with which it is connected. It is the magnitude of this opening that determines the quantity ot light transmitted to the retina. If, then, we are in a room illuminated with a strong lamp, the muscles which govern the opening of the pupil contract its dimensions until so much light only is admitted as is consistent with the healthful condition of the eye. If the lamp be suddenly extinguished, and the room be left dependent only on the light admitted by the windows, from the nocturnal firmament, we shall at first appear to be in profound darkness, but immediately the pupil will begin to expand, and -will presently become so enlarged that enough of light will be received into the eye to render the objects around \is faintly visible. If in this condition of the organ the lamp again be suddenly brought into the room, the eye will be pained by its light, and the eyelid will immediately drop to give it relief ; for the enlarge- ment of the pupil which has taken place to accommodate it to the faint light to which it was previously exposed, will admit so great a quantity of the strong light of the lamp as to hurt the retina, and the contraction of the pupil cannot be effected with sufficient rapidity to protect the organ from this injury. But the beneficent Maker of the eye has provided for this purpose the eyelid, which is capable of closing instantaneously, and which gives the pupil time to contract, and to accommodate its dimensions to the new condition to which it is exposed. 5. The perception we receive of the colour of an object \lepends often as much on the condition of the eye when the object is seen as upon the object itself. By the action of lights of different colours, the sensibility of the retina may be so modi- fied that the same object will appear at different times to have .litferent colours, and unreal objects will often be perceived. These are called spectra. If we place on a sheet of white paper a red wafer, and, illuminating, it strongly, direct the eye steadily to it for a short time, and then look at the paper close beside it, we shall there see a blue wafer of the same size. This object is an optical spectrum. The cause of its appearance is easily explained. By the action of the strong red light pro- ceeding from the wafer, the retina is rendered for the moment insensible to the operation of a more feeble red light upon it, for the same reason as the ear would be insensible to the ticking 85 POPULAR FALLACIES. of a clock immediately after being affected by a discharge ot artillery. Accordingly, when the eye, after viewing the red wafer, looks at a white paper beside it, the action of that portion of the compound white light reflected from the paper which is red fails to produce any perception, and the remaining constituents alone are perceived, which accordingly present a bluish tint. To comprehend this, and other similar illusions, it is very necessary to remember that white light is a compound of reds, yellows, and blues, and that if we deprive it of any one of these elements it will assume the tint produced by the others. Thus, if the eye be insensible to red light, all white objects will appear to it with a tint composed of yellow and blue. If it be insensible to blue light, then white objects will appear orange. Instances have more than once occurred, and are recorded in the works on optics, of individuals incapable, from ori- ginal defects of vision, of perceiving particular colours. The late Dr. Dalton, of Manchester, was a conspicuous example of this. But, as we have above stated, even a healthy and perfect eye will be rendered temporarily insensible to the impression ot particular colours by being exposed for a short time to the strong action of coloured lights. Optical illusions are produced in this way in the exhibition of fireworks. When luminous balls, some red and some white, are thrown up into the air, the white appear blue beside the red, and are generally imagined to be really blue. The effect, however, is a visual illusion, ascribable to the cause just explained. In the sky towards sunset, when reddish clouds are arranged with openings between them, the sky at such openings appears green, although it be really blue. In astronomical observations on the stars there is a curious case, in which it has never been settled whether the appearance is real or illusive. Many of the stars, which to the eye appear individual objects, prove to be double when examined with powerful telescopes. The two stars, thus composing a double star, are frequently of different colours, and it is found that when one is red the other is of a bluish tint. Now we know that it would appear of this tint, even though it were a white object, by reason of the presence of the red star. Whether, in these cases of double stars, the blue one would be really blue, or is rendered so by the optical effect adverted to, has not been decided, it being impossible to view it except in juxtaposition with its red companion. If the eye be directed to the sun for a few seconds, and the 86 SMELL, TASTE, AND TOUCH. eyelids then be closed, a blue spectrum of the sun will be seen, and will continue to be visible until the retina recover its state of repose. If we write a page or two with red ink, and then commence to write with black ink, the writing will appear of a light blue colour, and will continue to appear so until the retina loses the impression made by the red ink upon it. In passing, however, from the black to the red, no illusion is produced, the black not acting on the retina so as to excite it. If small holes be made in a red curtain, so as to admit the rays of the sun through them, the light which will be thrown upon a sheet of white paper will be the general redness produced by the semi-transparency of the curtain, with the white spots produced by the lights passing through the holes ; but these white spots will appear to the eyes blue. It will appear, from these observations, that effects are pro- duced by the juxtaposition of colours in objects of art independent of the separate properties of the colours themselves. Two colours, when seen in juxtaposition, do each of them appear to the eye different from what either would appear to be if seen separately from the other. 6. The senses of smelling, tasting, and even of feeling or touch, are liable to innumerable causes of deception. If the organ at the time it receives an impression be in any unusual condition, or even out of its usual position, the indication of the impression will be fallacious. If two fingers of the same hand, being crossed, be placed upon a table, and a marble or a pea is rolled between them, the impres- sion will be, if the eyes are closed, that two marbles or two peas are touched. If the nose be pinched, and cinnamon be tasted, it will taste like a common stick of deal. This is not a solitary instance. Many substances lose their flavour when the nostrils are stopped. Nurses, therefore, upon right and scientific principles stop the noses of children when they give them doses of disagreeable medicine. If things having different or opposite flavours be tasted alternately, in such rapid succession as not to allow the nerves of tasting to recover their state of repose, the power of dis- tinguishing flavour will be lost for the moment, and the sub- stances, however different, will be undistingnishable from one another. Thus, if the eyes be blindfolded, and buttermilk and claret be alternately tasted, the person tasting them, after a few repetitions of the process, will be unable to distinguish one from the other. S7 POPULAR FALLACIES. Tastes, like colours, in order to produce agreeable effects, should succeed each other in a certain order. Eating, considered us one of the fine arts in the most refined state of society, is regulated by principles, and nothing can shock the habits and rules of epicureanism more than the violation of certain rules in the succession and combination of dishes. It is maintained that perfection in the art of cookery and the observance of its principles at table is the surest mark of a nation's attainment of the highest state of civilisation. Of all the organs of sense, that whose nervous mechanism appears to be most easily deadened by excessive action is that of smelling. The most delightful odours can only be enjoyed occasionally, and for short intervals. The scent of the rose, or still more delicate odour of the magnolia, can be but fleeting pleasures, and are destined only for occasional enjoyment. He who lives in the garden connot smell the rose, and the wood- cutter in the southern forests of America is insensible to the odour of the magnolia. Persons who indulge in the use of artificial scents soon cease to be conscious of their presence, and can only stimulate their jaded organs by continually changing the objects of their enjoyment. 7. One of the most curious and most incomprehensible illusions of the senses is the singularly erroneous estimate which we make of the number of objects of any kind that are presented to us. A striking example of this is presented by the impression made upon the eye by the view of the firmament on a clear starlight night. The number of visible stars is always immensely over- estimated. Although it be true that the stars are, strictly speaking, countless in number, yet the number distinctly seen by the naked eye at any one time, unaided by the telescope, is not great. Any one can satisfy himself of this by examining any good map of the stars ; yet when we look at the firmament on a clear night, these objects appear to be inconceivably numerous. This illusion is dispelled by examining the heavens through the most ordinary telescope, or even by looking through a long tube, which will limit the view at any one moment to a small portion of the firmament. On the entire sphere of the heavens there are not above twenty stars of the first magnitude, and it is seldom that as many as six or eight of these can be seen at once. The number of stars of the second magnitude does not exceed fifty, and of these twenty are seldom seen at any one time. The stars of the third magnitude may amount to about two hundred, half of which only can be at the same time above the horizon. The small stars are much more numerous, but they are dis- 88 NUMBER AND DISTANCE. eernible with difficulty, and do not produce upon the mind the impression of multitude that we conceive. 8. It has been ascertained that the membrane of the eye, which is affected by light, retains the impression it has re- ceived for about the tenth of a second after the cause which produced the impression has been removed. When a lighted stick is whirled in a circle, the circle will appear to be one con- tinuous line of light, because the eye retains the impression which the light produces upon it at any point in the circle until the stick returns to that point. The light is, therefore, visible at the same time at every point of the circle. Ingenious optical toys are constructed, the effects of which are explicable on these principles. The same object is painted on the several divisions of the circumference of a circle in a succes- sion of different attitudes, and while the eye is directed to the highest point of the circle, through an opening made for that purpose, the circle is made to revolve, and the object passes before the eye in a succession of different attitudes. If the velocity with which the circle turns be such that the eye shall retain the impression of the object in one attitude until its picture in another attitude comes into view, it will have all the effect of a moving object. Waltzing figures and other similar devices are painted on circular cards and mounted, so as to give these effects. 9. If the eye is supplied with no external means of knowing the distance of a visible object, it estimates that distance by its apparent magnitude, and if there be any means of causing the magnitude of the same object to undergo a gradual change, the impression on the spectator is as if the object advanced to or receded from him. It is upon this principle that the exhibitions of phantasmagoria are made. The image of an object is formed on some surface prepared to receive it, the apartment being elsewhere in complete darkness, so that the observer has no means of knowing where the image is placed. The magic lantern has a power, by advancing it gradually toward the .nil-lace, to diminish the size of the image indefinitely, and by drawing it from the surface to augment it. The spectators, therefore, seeing the images gradually increase and diminish imagine they gradually approach to and recede from them. 10. Although the eye, by its direct as well as its indirect indications, supplies the greatest variety of impressions, of which many admit of exact numerical estimation, the touch, according to popular notions, is regarded as a more sure test of reality. The incredulous apostle, who refused to believe the evidence of his eyes, yielded to that of his touch. This sense is, never- 89 POPULAK FALLACIES. theless, confined within narrow and vague limits in most of its indications. If we take two heavy bodies in the hand, we shall, in many cases, be able to declare that one is heavier than the other ; but if we are asked whether one be exactly twice as heavy, or thrice as heavy as the other, we shall be utterly unable to decide. In like manner, if the weights be nearly equal, we shall be unable to declare whether they are exactly equal or not. If we look at two objects, differently illuminated, we shall in the same way be in some cases able to declare which is the more splendid ; but if their splendour be nearly equal, the eye will be incapable of determining whether the equality of illumination be exact or not. It is the same with heat. If two bodies be very different in temperature, the touch will sometimes inform us which is the hotter ; but if they be nearly equal, we shall be un- able to decide which has the greater or which the less temperature. The sense of touch, however, totally fails in informing us of the comparative quantities of heat in bodies. It cannot be at all affected by tha.t part of the heat of a body which is latent. Ice- cold water, and ice itself, feel to have the same temperature, and to contain the same quantity of heat : and yet it is proved that ice-cold water contains a great deal more heat than ice ; nay, that it can be compelled to part with its redundant heat, and to become ice ; and that this redundant heat, when so dismissed, may be made to boil a considerable quantity of water. But it is not only in the case of latent heat, which cannot be felt at all, that the touch fails to inform us of the quantities of heat in a body. Different bodies are raised to the same temperature by very different quantities of heat. If water and mercury, both at the temperature of 32, be touched, they will be felt to be both equally cold ; and if they be both raised to 100 and then touched, they will be felt to be both equally warm ; and the inference would be, that? equal quantities of heat must have been in the meanwhile communicated to them. Now, on the contrary, it has been proved that, in this case, the quantity of heat which has been communicated to the water is not less than thirty times the quantity which has been imparted to the mercury. In fact, to cause the same change of temperature, and, therefore, the same feeling of heat, in different bodies, requires very different quantities of heat to be imparted to them. It is plain, therefore, that the sense of touch totally fails in the discovery of the quantities of heat which must be added to different bodies, in order to produce in them the same change of temperature. The thermometer, the scientific measure of temperature, is here, however, in the same predicament as the sense of feeling, HEAT AND COLD. since the unequal additions of heat given to the water and the mercury produce precisely the same effects upon it. But even though we omit the consideration of the relative quantities of heat that produce equal changes of temperature in different bodies, the sense of feeling will still be found most fallacious in the indications which it gives of temperature itself ; and here, indeed, the error and confusion into which it is apt to lead, when unaided by the results of science, are very conspicuous. The air of a cave, if it be sufficiently deep, will feel cold in summer, and warm in winter. If a thermometer be suspended in it, it will prove that its temperature is always the same. In summer, that temperature being below that of the general atmosphere, the cave feels cold ; in winter, being above it, the cave feels warm. The same thermometer which has been kept for sixty years in the vaults of the Observatory at Paris, at the depth of eighty-eight feet below the surface, has shown, during that interval, the temperature of 11 -82 Cent., which is equal to 53 ;p Fahr., without varying more than half a degree of Fahr., and even this variation, small as it is, has been explained by the effects of currents of air produced by the quarrying operations in the neighbourhood of the Observatory. It appears, therefore, that our perception of heat or cold depends not alone on the thermal state of the bodies which affect us, but also on the state of our own bodies at the moment. These perceptions are, in effect, relative, and not absolute. One body feels cold because it is below, and another warm because it is above, the temperature of our own bodies. It follows, therefore, that if we reduce, by any expedient, different members of our bodies to different states of warmth, n,ny external object which has one intermediate temperature will feel warm to the colder, and cold to the warmer member. This experiment may be easily tried. If we hold the hand in water which has a temperature of about 90, after the agitation of the liquid has ceased, we shall become wholly insensible of its presence, and shall be unconscious that the hand is in contact with any body whatever. "We shall, of course, be altogether unconscious of the temperature of the water. Having held both hands in this water, let us now remove the one to water at a temperature of 200, and the other to water at the temperature of 32. After holding the hands for some time in this manner, let them be both removed, and again immersed in the water at 90 ; immediately we shall become sensible of warmth in the one hand, and cold in the other. To the hand which had been immersed in the cold water, the water at 90 will feel hot, and to the hand which had been immersed in the water at 200, the 91 POPULAR FALLACIES. water at 90 will feel cold. If, therefore, the touch be in this case taken as the evidence of temperature, the same water \vill be judged to be hot and cold at the same time. I have elsewhere indicated several curious examples of the fallacies of the senses of feeling in relation to the temperature of bodies.* Even when the state of our bodies is the same, and the tem- perature of external objects the same, different objects will feel to us to have different degrees of heat. If we immerse the naked body in a bath of water at the temperature of 120, and, after remaining for some time immersed, pass into a room in which the air and every object is raised to the same temperature, we shall experience, on passing from the water into the air, a sensa- tion of coldness. If we touch different objects in the room, all of which are at the temperature of 120, we shall nevertheless acquire very different perceptions of heat. When the naked foot rests on a mat or carpet, a sense of gentle warmth is felt ; but if it be removed to the tiles of the floor, heat is felt sufficient to produce inconvenience. If the hand be laid on a marble ehimney-piece, a strong heat is likewise felt, and a still greater heat on any metallic object in the room. Walls and woodwork will be felt warmer than the matting, or the clothes which are put on the person. Now, all these objects are, nevertheless, at the same temperature. From this chamber let us suppose that we pass into one at a low temperature ; the relative heats of all the objects will now be found to be reversed the matting, carpeting, and woollen objects, will feel the most warm ; the woodwork and furniture will feel colder ; the marble colder still ; and "metallic objects the coldest of all. Nevertheless here, again, all the objects are exactly at the same temperature, as may be in like manner ascertained by the thermometer. In the ordinary state of an apartment, at any season of tlio year, the objects which are in it all have the same temperature, and yet to the touch they will feel warm or cold in different degrees : the metallic objects will be coldest ; stone and marble Jess so ; wood still less so ; and carpeting and woollen objects will feel warm. When we bathe in the sea, or in a cold bath, we are accus- tomed to consider the water as colder than the air, and the air colder than the clothes which surround us. Now all these objects are, in fact, at the same temperature. A thermometer, surrounded by the cloth of our coat, or suspended in the atmosphere, or immersed in the sea, will stand at the same temperature. * Treatise on Heat, p. 372. 92 HEAT AND COLD. A linen shirt when first put on will feel colder than a cotton one, and a flannel shirt will actually feel warm ; yet all these have the same temperature. The sheets of the bed feel cold, and blankets warm ; the blankets and sheets, however, are equally warm. A still, calm atmosphere, in summer, feels warm ; but if a wind arises, the same atmosphere feels cold. Xow a thermometer, suspended under shelter, and in a calm place, will indicate exactly the same temperature as a thermometer on which the wind blows. 11. These circumstance may be satisfactorily explained, when it is considered that the human body maintains itself almost invari- ably, in all situations, and at all parts of the globe, at the tem- perature of 96 ; that a sensation of cold is produced when heat is withdrawn from any part of the body faster than it is generated in the animal system ; and, on the other hand, warmth is felt when either the natural escape of the heat generated is intercepted, or when some object is placed in contact with the body which has a higher temperature than that of the body, and consequently imparts heat to it. The transition of heat from the body to any object when that object has a lower temperature, or from the object to the body when it has a higher temperature, depends, in a certain degree, on the conducting power of the objects severally, and the transition will be slow or rapid, according to that conducting power. An object, therefore, which is a good conductor of heat, if it has a lower temperature than the body, carries off heat quickly, and feels cold ; if it has a higher temperature than the body, it com- municates heat quickly, and feels hot. A bad conductor, on the other hand, carries off and communi- cates heat very slowly, and therefore, though at a lower tem- perature than the body, is not felt to be colder, and, though at a higher temperature, not felt to be warm. Most of the apparent contradictions which have been already adduced in the results of sensation, compared with thermometric indications, may be easily understood by these principles. When we pass from a hot bath into a room of the same temperature, the air, though at a higher temperature than our body, communicates heat to it more slowly than the water because, being a more rare and attenuated substance, a less number of its particles are in actual contact with the body ; and also such particles as are in contact with the body take almost the same temperature as the body, and adhere to it, forming a sort of coating or shield, by which the body is defended from the effects of the hotter part of the surrounding atmosphere. A carpet, being a bad conductor of heat, fails to transmit heat to POPULAR FALLACIES. the foot, and therefore, though at a higher temperature than the body, creates no sensation of warmth. The tiles and marble, being better conductors of heat, and at a higher temperature than' the body, transmit heat readily, and metallic objects still more so : these, therefore, feel hot. On passing into a cold room, the very contrary effects ensue. Here all the objects have a temperature below that of the body ; the ca'rpet and other bad conductors, not being capable of receiving heat when touched, produce no sensation of cold ; wood, being a better conductor, feels cooler ; marble, being a better conductor, gives a still stronger sensation of cold ; and metal, the best of all conductors, produces that sensation in a still greater degree. In cold temperatures, the particles of water which carry off the heat from the body are far more numerous than those of air, and therefore carry the heat off more rapidly ; and, besides, they are constantly changing their position ; the particles warmed by the body immediately ascend by their levity, and cold particles come into contact with the skin. Thus water, although a bad conductor of heat, has the same effect as a good conductor, by the effect of its currents. Sheets feel colder than the blankets, because they are better conductors of heat, and carry off the heat more rapidly from the body ; but when, by the continuance of the body between them, they acquire the same temperature, they will then feel even warmer than the blanket itself. Hence it may be understood why flannel, worn next the skin, forms a warm clothing in cold climates, and a cool covering in hot climates. To explain the apparent contradiction implied in the fact that the use of a fan produces a sensation of coldness, even though the air which it agitates is not in any degree altered in tempera- ture, it is necessary to consider that the air which surrounds us is generally at a lower temperature than that of the body. If the air be calm and still, the particles which are in immediate contact with the skin acquire the temperature of the skin itself, and, having a sort of molecular attraction, they adhere to the skin in the same manner as particles of air are found to adhere to the surface of glass in philosophical experiments. Thus sticking to the skin, they form a sort of warm covering for it, and speedily acquire its temperature. The fan, however, by the agitation which it produces, continually expels the particles thus in contact with the skin, and brings new particles into that situation. Each particle of air, as it strikes the skin, takes heat from it by contact, and, being driven off, carries that heat with it, thus producing a constant sensation of refreshing coolness. Now from this reasoning it would follow that, if we were 94 FIRE-EATERS AND MOUNTEBANKS. placed in a room in which the atmosphere has a higher tempera- than 96, the use of a fan would have exactly opposite effects, and, instead of cooling, would aggravate the effects of heat ; and such would, in fact, take place. A succession of hot particles would, therefore, be driven against the skin, while the particles which would be cooled by the skin itself would be constantly removed. 12. It may be objected to some of the preceding reasonings, that glass and porcelain, though among the worst conductors of heat, generally feel cold. This, however, is easily explained. When the surface of glass is first touched, in consequence of its density and extreme smoothness, a great number of particles come into contact with the skin ; each of these particles, having a tendency to an equilibrium of temperature, takes heat from the skin, until they acquire the same temperature as the body which is in contact with them. When the surface of the glass, or perhaps the particles to some very small depth within it, have acquired the temperature of the skin, then the glass will cease to feel cold, because its bad conducting power does not enable it to attract more heat from the body. In fact, the glass will only feel cold to the touch for a short space of time after it is first touched. The same observation will apply to porcelain and other bodies which are bad conductors, and yet which are dense and smooth. On the other hand, a mass of metal, when touched, will continue to be felt cold for any length of time, and the hand will be inca- pable of warming it, as was the case with the glass. A silver or metallic tea-pot is never constructed with a handle of the same metal, while a porcelain teapot always has a porcelain handle. The reason of this is, that metal being a good conductor of heat, the handle of the silver or other metallic teapot would speedily acquire the same temperature as the water which the vessel contains, and it would be impossible to apply the hand to it without pain. On the other hand, it is usual to place a wooden or ivory handle on a metal teapot. These substances being bad conductors of heat, the handle will be slow to take the temperature of the metal, and even if it does take it, will not produce the same sensation of heat in the hand. A handle, apparently silver, is sometimes put on a silver teapot, but, it examined, it will be found that the covering only is silver ; and that at the points where the handle joins the vessel, there is a small interruption between the metallic covering and the metal of the teapot itself, which space is sufficient to interrupt the communication of heat to the silver which covers the handle. In a porcelain teapot, the heat is slowly transmitted from the vessel to its handle ; and even when it is transmitted, the handle, being a bad conductor, may be touched without inconvenience. 95 POPULAR FALLACIES. A kettle which lias a metal handle cannot be touched, wheiu filled with boiling water, without a covering of some non-con- ducting substance, such as cloth, or paper, while one with a wooden handle may be touched without inconvenience. 13. The feats sometimes performed by quacks and mounte- banks, in exposing their bodies to fierce temperatures, may be easily explained on the principle here laid down. When a man goes into an oven, raised to a very high temperature, he takes care to have under his feet a thick mat of straw, wool, or other non-conducting substance, upon which he may stand with impu- nity at the proposed temperature. His body is surrounded with air, raised, it is true, to a high temperature, but the extreme tenuity of this fluid causes all that portion of it in con- tact with the body, at any given time, to produce but a slight effect in communicating heat. The exhibitor always takes care to be out of contact with any good conducting substance ; and when he exhibits the effect produced by the oven in which he is enclosed, upon other objects, he takes equal care to place them in a condition very different from that in which he, himself, is placed ; he exposes them to the effect of metal or other good conductors. Meat has been exhibited, dressed in the apart- ment with the exhibitor ; a metal surface is, in such a case provided, and probably heated to a much higher temperature than the atmosphere which surrounds the exhibitor. THAUMATROPE. VIEW OF GREENWICH OBSERVATORY, SHOWING THE SIGNAL-BALL AT THE TOP OF THE DOME. LATITUDES AND LONGITUDES. 1. Necessary to know our position on the earth. 2. Poles and equator. 3. Parallel of latitude. 4. Meridian of Greenwich. 5. Latitude and longitude. 6. Methods of determining the latitude. 7. By the sun. 8. By stars. 9. Hadley's sextant. 10. Latitude at sea. 11. To find the longitude. 12. Lunar method. 13. Ball signal at Greenwich. 1. BEFORE it is possible to acquire a distinct knowledge of the position or distances of any bodies in the universe outside the surface of the earth, it is first indispensable that we, who have to make these calculations, should distinctly ascertain our own position in reference tc the bodies we observe. But as our posi- tion is subject to continual change, as well by reason of the diurnal rotation of the earth upon its axis, on the surface of which we are carried round, as by the annual motion of the globe in its orbit round the sun, we are obliged as a necessary prelimi- nary to analyse with accuracy all the circumstances of these LARDNER'S MUSEUM OF SCIENCE, No. 5. H 97 LATITUDES AND LONGITUDES. motions. But even before we are in a condition to accomplish this, there is another preliminary step not.less v indisp^nsable, \vhich is to ascertain our own position on the surface of the globe we inhabit. This is not so easy a matter as at the first view it might seem to be. The earth we dwell on is a globe which com- pared with any familiar standards of measure has a stupendous magnitude. The range of pur vision -around any situation which we may occupy upon the surface of this globe is small. In the most unobstructed situation we can obtain that which is pre- sented us at sea, when out of sight of land, on the clearest day our observation is circumscribed by a radius of a few miles. The portion of the surface which we see at one and the same time, forms in reality so small a patch of the globe of the earth, that it is only by indirect reasoning that we can recognise upon it any character save that of a flat plane. How, then, are we to know in what part of the terrestrial globe that small patch of surface is situated ? 2. To answer this question, it is evidently necessary first to settle some fixed points or lines to which we may refer various places, and by which we may express their positions. The points which have been usually selected for this purpose are the POLES and the EQUATOR. The poles are those points on the surface of the earth where the axis on which it performs its diurnal rota- tion terminates, and they are distinguished, as is well known, by the names of the NORTH and SOUTH poles. If we imagine a circle drawn round the globe in such a manner as to divide it into two hemispheres, having in the midst of one the north pole, and in the midst of the other the south pole, such a circle is called the EQUATOR, from equally dividing the globe. Every point in this circle will be at the same distance from the poles, and if we imagine the globe to be cut by a plane through the poles, that plane will be at right angles to this circle, and the section it forms will be what is called a TERRES- TRIAL MERIDIAN. The arc of this meridian between either pole and the equator will be one quarter of its entire circumference, and will therefore be 90. The equator is, therefore, everywhere 90 from each of the poles. In fig. 1, N is the north and s the south pole, and EQ is the equator. The hemispheres into which the equator divides the earth are called the NORTHERN and SOUTHERN HEMISPHERES. That which includes the north pole, being the northern, and that which includes the south pole, the southern. The position of a place in either hemisphere with reference to 98 POLES AND EQUATOR. the equator is expressed by stating the number of degrees of a terrestrial meridian included between the place and the equator. This is called the LATITUDE of the place ; which is the distance of the place from the equator expressed in degrees of the meri- dian. Thus, if a place be midway between the pole and the equator, its latitude is 45. If it be distant from the equator by two-thirds of the entire distance from the equator to the pole, its latitude will be 60, and so on. 3. The latitude is said to be northern and southern/according as the place is in the northern or southern hemisphere. But it is evident that the latitude alone will be insufficient for the determination of the position of a place. If we state that a certain place is 45 north of the equator, it will be impossible to ascertain certainly the place in question, inasmuch as there is a circle of points on the earth, all of which are 45 north of the equator. If we suppose a circle drawn round the surface of the northern hemisphere parallel to the equator, at the distance from the equator of 45 3 , every point of such circle will be equally characterised by the latitude of 45 north. Such a circle is called a PARALLEL OF LATITUDE, and it is therefore apparent that wherever such a parallel may be drawn upon the earth, all the places upon it will have the same latitude. In the figure E N Q is the northern and E s Q the southern H 2 9 LATITUDES AND LONGITUDES. hemisphere. The circles L L, are northern and I I, southern parallels of latitude. All places situate upon any one of these circles have the same latitude. The distances of N and s from E Q, being 90 that is the latitude of the poles. The circles N m s and N n s, drawn upon the earth from pole to pole intersect the equator E Q, and all the parallels L L, II, at right angles. These are TERRESTRIAL meridians. The latitude is, then, insufficient to determine the position of any place. How, then, it may be asked, can the exact position of any place be expressed ] 4. Let us suppose that a meridian is arbitrarily selected, passing through some particular place, such as the Greenwich Observa- tory. We may conceive another meridian drawn upon the earth east or west of that, so that the two meridians shall include between them an arc of the equator,' consisting of a definite number of degrees ; say, for example, that it shall consist of 20 ; then such a meridian will be defined by stating that it is 20 east or west of the meridian of Greenwich. All that can be settled by such a statement is the position of the meridian in which the place lies with reference to the arbitrarily chosen meridian of Greenwich. This relative position of the two meridians is called the LONGITUDE OF THE PLACE. As the meridian from which the longitude is measured is altogether arbitrary, there being no physical or geographical reason why one meridian should be chosen rather than another, each nation has naturally selected as the zero of longitude the meridian of some noted place in its precincts. In England the Eoyal Observatory at Greenwich has been the place selected, and accordingly in all English works on geography, political and physical, longitudes are invariably expressed in reference to the meridian of Greenwich. It will, therefore, be most convenient for us here to refer to that meridian. When these explanations are clearly understood, we shall be in a condition, distinctly and definitely, to express the position of a place upon the surface of the globe of the earth. If we state its latitude and its longitude, we can fix at once, and unequivo- cally, the position of a place. Thus, let us suppose that its latitude is 50 north, its longitude 30 east of Greenwich ; its position will be found by imagining a circle parallel to the equator drawn upon the northern hemisphere at a distance of 50 from the equator ; then, supposing a meridian drawn through Greenwich, intersecting this parallel, and another drawn so as to cross the equator at a point 30 east of the former ; the place in question will be upon the line parallel to the equator first drawn, inasmuch as it will be 50 north of the 100 POSITION OF A PLACE. equator, and it will be also in the meridian last drawn, inasmuch as it will be 30 east of Greenwich. Since, then, it will be at the same time on both these lines, it will necessarily be at the point where they cross each other at the east of the standard meridian of Greenwich. 5. Thus, then, we have succeeded at least in establishing stand- ards of position and a nomenclature by which the exact position of a place on the surface of the globe can be expressed. But we have still another much more important and difficult question to settle. How are we to discover in what part of the globe any place is which we may occupy at a given time ; in other words, how are we to discover its latitude and its longitude ? These are questions, especially the latter, attended with some difficulty, and which have been solved by different methods, applicable in different cases, according to the circumstances under which the position of the place is sought, and the purpose for which such position is to be determined. At any place on land where the geographical position is once determined, it may be recorded, so as to be permanently known for the future without a repetition of the process for determining it ; but it is otherwise at sea. On the trackless surface of the deep all marks of events and operations are immediately oblite- rated, and a new investigation must be instituted in every ease when the position of any point is to be determined. The mariner must, therefore, be supplied not only with the means of deter- mining the position of his ship at all times, but with means the application of which is practicable under the peculiar circum- stances in which he is placed. The instruments he uses must not only be portable, but must be such as may admit of being manipulated, subject to the disturbances and the vicissitudes of the sea. The objects of his observations must be such as are almost always in his view. It is evident, then, that the problem, as applicable on land, is wholly different in its circumstances and conditions from that which is applied on the deep. But even on land the problem presents itself under various circumstances and conditions. In the fixed observatory, where the observer is supplied with instruments of the greatest magnitude, of the most refined accuracy, and the most absolute stability, methods have been used which are susceptible of the last conceivable degree of accuracy, and accordingly the position of those points on the globe where such observatories have been erected are usually determined with the greatest degree of precision. Such points on the globe serve, therefore, as a sort of landmarks, relative to which the position of all surrounding places may be deter- mined. 101 LATITUDES AND LONGITUDES. The circumstances under which the scientific traveller and geegrapher makes his observations, with a view to the general determination of the points of a country, are less favourable to accuracy than those available to the astronomer, but still are more susceptible of precision than those which can be placed at the disposal of the mariner. It is, however, the business and the duty of those who devote their lives to the advancement of the sciences, to supply to each class of observers those instruments and methods of inquiry which are capable, respectively of giving results which, in the circumstances of the case, have the greatest attainable accuracy. TO FIND THE LATITUDE. 6. Let us suppose the globe of the earth to be represented at O, and let N be its north pole, and E its equator ; let P be a place upon it, whose latitude, that is, whose distance from the equator is to be determined. Let n Z e represent the firmament sur- rounding the globe at an indefinite distance. The point n, immediately over the north pole, and which is in fact the con- tinuation of the line O N, will be the place of the north pole in the heavens, very near to which is a star, called the Polar star. The point e, in the continuation of the line O E, will be that which is directly over the equator, and will be that point in the heavens representing the position of the equator j and the point Z, in the continuation of the line O P, the point of the heavens which is directly over the observer at the place P, will be that which is called his zenith. This point is that to which a plumb line would direct itself. Now the points n, Z, and e are the points in the firmament which correspond with the points N, P, and E, upon the earth, and it is evident that whatever arcs of the terrestrial meridian N P E are included between these points, similar arcs of the celestial meridian must be included between the points n Z e. If, then, P E were 40, Z e must also be 40, just as n e is 90, while N E is also 90. In short, the zenith of any place in the heavens is the point in the firmament which corresponds with the position of the place on the globe, and the distance of the zenith in the heavens of one place from the zenith of another, must necessarily be the same in degrees as the distance between two places on earth. Thus Z is the zenith of P ; e is the zenith of E ; Z is the same number of degrees from e as P is from E. This being clearly understood, it is evident that if we can, by any means ascertain by observations, 102 TO FIND THE LATITUDE. the distance from Z to n, we can infer at once the distance from P to E, and hence can discover the latitude of the place. It is apparent, theii, if we can observe the distance of the zenith of any place from the celestial pole, that will give us the distance in degrees of the place itself from the terrestrial pole, and by subtracting that from 90, we shall obtain the distance of the place itself from the equator, or what is the same, its lati- tude. As an example of this, let us suppose that in' measuring Fig. 2. \ the distance from Z to n we find it to be 50, we infer, therefore, that since the distance of the zenith from the pole is 50, the dis- tance of the place from the terrestrial pole is also 50. But since the terrestrial pole is 90 from the equator, it follows that the distance of the place from the equator must be 40, and it is north or south, according as the zenith of the place is in the northern or southern hemsiphere of the firmament. Thus, then, it appears that the latitude of a place can always be found, provided we can measure the distance of its zenith from the celestial pole ; and this, of course, can always be done by the use of proper instruments, provided that the zenith and the pole can be distinctly seen. Now the direction of the zenith can always be determined by the plumb line ; but although the 103 LATITUDES AND LONGITUDES. pole star is very near the pole, it is not exactly at it ; there is, in fact, no star exactly at the pole, and there being no visible object there, it is impossible to measure directly its distance from the zenith. This difficulty is eluded by measuring the distance of the zenith from some star, or other celestial object, whose distance from the pole happens to be known : for example, suppose that there were a star directly between the zenith and pole, whose distance from the pole was known to be 10. Then if we find the distance of the zenith from this star to be 40, we should immediately infer the distance of the zenith from the pole to be 50. It is in fact, then, by this device that the latitude is always ascertained. By various observations made by astronomers, the positions of most of the stars and other celestial objects, with respect to the poles, are known and recorded ; and when we desire to determine the latitude of any place, we measure the distance of the zenith of that place from some celestial object whose position with respect to the pole is known, and thence infer the position of the place with respect to the terrestrial pole ; and from that deduce at once the latitude. 7. But our purpose would be equally served if we were supplied with the position of any visible object with reference to the celestial equator. Thus, if we know the distance of the centre ot the sun from the celestial equator, we shall readily be able to find the latitude ; for it would only be necessary when the sun is in or very near the meridian, that is, at or near noon, to measure the distance of the zenith of the place from the centre of the sun. This would be done by measuring the distance of the zenith, first from the upper, and then from the lower limb of the sun. The distance from the centre would be the mean between these. Let us suppose, for example, that the sun being between the zenith and the equator, we find that the distance from the zenith to the centre of the sun is 20, and that we also ascertain from* the table of the position of the sun, that the distance of the centre of the sun at that time from the equator, is also 20, we should infer at once that the distance of the zenith from the equator must be 40, and that such, therefore, must be the latitude of the place. This method of ascertaining the latitude is, perhaps, the most easily practicable. The observations may be performed daily, at noon, when the sun is visible : and in all almanacs, the distance of the centre of the sun from the equator, which is called the sun's declination, is registered. The instrument by which the observations are executed on land is, usually, a quadrant fur- 104 LATITUDE BY THE LINE. nished with a telescope moving upon its centre. One radius of the quadrant is placed in the direction of the plumb line, and therefore points to the zenith. The telescope moves round the centre until it is directed to the object whose distance from the zenith is to be observed. The angle between the telescope and the vertical radius of the quadrant will then be the same as the distance of the object from the zenith, 8. In astronomical observatories methods of observation have been applied susceptible of much greater accuracy. Stars upon the meridian can there be used with great advantage. The distances of these stars from the pole are accurately known, and the astronomer selects for his observation those conspicuous stars which pass near to his zenith. He observes the arc of the celestial meridian between his aenith and these stars. And from the magnitude of the arc and the distance of the star of the celestial pole, he discovers the distance of the zenith from the pole and thence the latitude. The principal source of accuracy in this method is, that the distance between the zenith and the star being very small, is capable of more exact measurement, for reasons connected with the structure of the astronomical instrument, than could be attained in the measurement of greater angles. 9. In observations made at sea, it is not practicable, however, to use the plumb line, and indeed, even for the purposes of geogra- phers it is not always convenient. An admirable instrument has been invented equally applicable to observations by land or by water, called Hartley's sextant, by means of which the obser- vations can be made with reference to the horizon, independent of the zenith, and therefore independent of the plumb line. It is not our purpose here to enter into a description of the principles and structure of this celebrated and most useful instrument. It will be sufficient for the present purpose to state that it is capable of being applied to the measurement of the angular distances between any two visible objects with a very great degree of precision, and that it may be used with facility, even when the position of the observer is subject to all the unsteadiness incidental to the condition of the mariner. When this instrument is used, instead of observing the dis- tance of any object from the zenith, we observe its distance from the horizon, which will answer the same purpose, inasmuch as that whenever the distance of an object from the horizon is known, its distance from the zenith can be found, since the distance from the zenith to the horizon being 90, if we subtract the distance of the object from that, the remainder will be the distance of the object from the zenith. 105 LATITUDES AND LONGITUDES. At sea we have generally, indeed almost always, a well-defined horizon. If the mariner desires to measure the altitude of an object, he has only to measure the distance of the object from the horizon in a direction perpendicular to it, and this he is enabled to do with a little practice, with admirable facility and precision, with Hadley's sextant. 10. Let us see, then, how the mariner is thus enabled daily to determine the latitude of his ship. As noon approaches, the sky being sufficiently clear to render the disc of the sun visible, he applies the instrument and finds the altitudes of the lower and upper limbs of the sun from the verge of the horizon. The mean of these will be the altitude of the sun's centre. If this altitude be taken from 90, the remainder will be the distance of the sun's centre from the zenith. He finds in his almanac the distance of the centre of the sun on that day from the equator, and hence he at once, as already explained, obtains the distance of his zenith from the equator; that is the latitude of the ship. There are several minute circumstances observed in the prac- tice of this problem, which do not affect its general spirit, and the introduction of which here would be unsuitable to our object ; we therefore omit them. Thus we see that, whether by sea or by land whether in the observatory of the astronomer, traversing the sands of the desert or the forests of America, or voyaging over the trackless and unimpressible surface of the ocean we are in every case by science supplied with suitable and practicable means by which we can ascertain the distance of the place where we are, north or south, on the globe. TO DETERMINE THE LONGITUDE. 11. In expressing and determining the latitude of a place, we have fixed points and lines on the firmament to refer to such as the celestial pole and equator ; and to find it, nothing more is necessary than to ascertain the position of the zenith of the place with reference to these. But with respect to the longitude, the case is very different ; it is impossible even to express the longitude without involving a reference to two places at least that of which we wish to determine the longitude, and that which is selected as the starting point from which all longitudes are to be measured. If we could observe in the firmament the two points which at the same time form the zeniths of the two places, then the difference of their longitudes could be found by 106 TO FIND THE LONGITUDE. noting the times at which these two points would cross the meridian of the place whose longitude is to be determined. To comprehend fully the spirit of the celebrated problem of finding the longitude, we must imagine the globe of the earth turning on its axis, having around it the starry firmament. Let us suppose A B c, a b c, to be the parallel of latitude of the place P, whose longitude is to be determined, p being the pole, and let M z N represent the firmament. Let the zenith be the point on Fig. 3. the firmament marked by z. If we suppose the globe to turn upon its axis in the direction of A B c, a b c, the place p will, by its rotation be carried to the right of z, and the same point z will become successively the zenith of the points c B and A ; and, in fact, every point in the parallel of latitude will successively come under the point z, which will be, therefore, in regular succession, their zenith points. In twenty-four hours, or, more accurately, in twenty-three hours and fifty-six minutes, the globe will make its complete revolution ; therefore three hundred and sixty degrees of the parallel will successively pass under the same point of the firmament. 107 LATITUDES AND LONGITUDES. By knowing exactly the time of rotation of the earth, and having ascertained that its diurnal motion is uniform, we can determine by simple arithmetic what extent of its surface will pass, in a given time, under any point of the firmament. Thus if we say in round numbers that the whole circumference cor- responds to twenty-four hours, it will follow that fifteen degrees will move under the point z each hour, or one degree in four minutes. If we suppose z to represent the place of the sun, then it will be noon, or twelve o'clock, at the place which is immediately under z ; that is, at p. If c be fifteen degrees west of p, then it will arrive under z one hour after p ; consequently, when it is noon at p it is eleven o'clock at a place fifteen degrees to the west of p ; and, for the same reason, it is ten o'clock at a place thirty degrees to the west of p, and so on. Again : if a be a place fifteen degrees to the east of p, a must have been under z an hour before p reached it. It will be noon, therefore, at ly be inferred that the moon has no influence whatever in this case. Among the maxims of Pliny we find that grapes should be dried by night at new moon, and by day at full moon. Wheu the moon is new it is below the horizon during the night, and above it during the day ; and when it is full it is above the horizon during the night, and below it during the day. The maxim of Pliny, therefore, is equivalent to a condition requiring that the grapes should be dried when the moon is below the horizon. It is evident that the absence of the moon is not required in this case in consequence of any effect which her light might produce if she were present ; for when the moon is new she affords no light, even when in the firmament, the illuminated side being turned from the earth. If the maxim be founded upon any reason, it must, therefore, either be on some influence which the moon is supposed to produce when present, independent of her light (the absence of which influence is desired), or it may be that she may be supposed to transmit some effect through the solid mass of the earth when on the other side of it which she is incapable of producicg without its intervention. The maxim is probably as absurd and groundless as the other effects imputed to the moon. 5. Supposed Lunar Influence on the Complexion. It is a prevalent popular notion in some parts of Europe, that the moon's light is attended with the effect of darkening the complexion. That light has an effect upon the colour of material substances is a fact well known in physics and in the arts. The process of bleaching by exposure to the sun is an obvious example of this class of facts. Vegetables and flowers which grow in a situation excluded from the light of the sun are different in colour from those which have been exposed to its influence. The most striking instance, however, of the effect of certain rays of solar light in blackening a light -coloured substance, is afforded by chloride of silver, which is a white substance, but which imme- diately becomes black when acted upon by the rays near the violet extremity of the spectrum. This substance, however, highly susceptible as it is of having its colour affected by light, is, nevertheless, found not to be changed in any sensible degree when exposed to the light of the moon, even when that light is condensed by the most powerful burning lenses. It would seem, therefore, that as far as any analogy can be derived from the qua- lities of this substance, the popular impression of the influence of the moon's rays in blackening the skin receives no support. M. Arago (who generally inclined to favour rather than oppose prevailing popular opinions), thought it possible that 121 LUNAR INFLUENCES. some effect may be produced upon the skin exposed on clear nights, explicable on the same principle as that by which we have explained the effects erroneously imputed to what is called the red moon. The skin being, in common with the leaves and flowers of vegetables, a good radiator of heat, will, when exposed on a clear night, for the same reasons, sustain a loss of tempera- ture. Although this will be to a certain extent restored by the sources of animal heat, still it may be contended that the cooling produced by radiation is not altogether without effect. It is well known that a person who sleeps exposed in the open air on a night when the dew falls, is liable to suffer from severe cold, although the atmosphere around him never falls below a moderate temperature ; and although no actual deposition of dew may take place upon his skin. This effect must arise from the constant lowering of temperature of the skin by radiation. The Hdle du bivouack is a term familiar to all French soldiers who have taken much part in campaigns. Hale is a term which expresses a certain supposed quality of the atmosphere, by which it produces the effect of tanning or darkening the skin. It is well known to the soldier that it takes place only on un- clouded nights when the face is exposed to the sky. That it is not a mere quality of the atmosphere is proved by the fact that any screen which will intercept the view of the sky will protect the face, however much it be otherwise exposed to the air. In the south of France mothers warn their daughters against nocturnal promenades by the old proverb : " Que lou sol y la sereine Fan veni la gent mouraine." It is remarkable that this proverb is current in places where the moon is not noticed as concerned in the effect produced. 6. Supposed Lunar Influence on Putrefaction. Pliny and Plutarch have transmitted it as a maxim, that the light of the moon facilitates the putrefaction of animal substances, and covers them with moisture. The same opinion prevails in the West Indies, and in South America. An impression is prevalent, also, that certain kinds of fish exposed to moonlight lose their flavour and become soft and flabby ; and that if a wounded mule be ex- posed to the light of the moon during the night, the wound will become irritated, and frequently become incurable. Such effects, if real, may be explained upon the same prin- ciples as those by which we have already explained the effects imputed to the red moon. Animal substances exposed to a clear 122 LUNACY AND OTHEK MALADIES. sky at night, are liable to receive a deposition of dew, which humidity has a tendency to accelerate putrefaction. . But this effect will be produced if the sky be clear, whether the moon be above the horizon or not. The moon, therefore, in this case, is a witness and not an agent ; and we must acquit her of the misdeeds imputed to her. 7. Supposed Lunar Influence on Shellfish. It is a very ancient remark, that oysters and other shell-fish become larger during the increase than during the decline of the moon. This maxim is mentioned by the poet Lucilius, by Aulus Gellius, and others : and the members of the academy del Cimento appear to have tacitly admitted it, since they endeavour to give an explanation of it. The fact, however, has been carefully examined by Eohault, who has compared shell-fish taken at all periods of the lunar month, and found that they exhibit no difference of quality. 8. Supposed Lunar Influence on the Marrow of Animals. An opinion is prevalent among butchers that the marrow found in the bones of animals varies in quantity according to the phase of the moon in which they are slaughtered. This question has also been examined by Rohault, who made a series of observations which were continued for twenty years with a view to test it ; and the result was that it .was proved completely destitute of foundation. 9. Supposed Lunar Influence on the Weight of the Human Body. Sanctorius, whose name is celebrated in physics for the invention of the thermometer, held it as a principle that a healthy man gained two pounds weight at the beginning of every lunar month, which he lost towards its completion. This opinion appears to be founded on experiments made upon himself ; and affords another instance of a fortuitous coincidence hastily gene- ralised. The error would have been corrected if he had continued his observations a sufficient length of time. 10. Supposed Lunar Influence on Births. It is a prevalent opinion that births occur more frequently in the decline of the moon than in her increase. This opinion has been tested by comparing the number of births with the periods of the lunar phases ; but the attention directed to statistics as well in this country as abroad, will soon lead to the decision of this question. Other sexual phenomena, vulgarly supposed to have some relation to the lunar month, have no relation whatever to that period. 11. Supposed Lunar Influence on Incubation. It is a maxim handed down by Pliny, that eggs should be put to hatch when the moon is new. In France it is a maxim generally adopted, that the fowls are better and more successfully reared when 123 LUNAE INFLUENCES. they break the shell at the full of the moon. The experiments and observations of M. Girou de Buzareingues have given counte- nance to this opinion. But such observations require to be multiplied before the maxim can be considered as established. M. Girou inclines to the opinion that during the dark nights about new moon the hens sit so undisturbed that they either kill their young or check their development by too much heat ; while in moonlight nights, being more restless, this effect is not produced. 12. Supposed Lunar Influence on Mental Derangement and other Human Maladies. The influence on the phenomena of human maladies imputed to the moon is very ancient. Hippo- crates had so strong a faith in the influence of celestial objects upon animated beings, that he expressly recommends no physician to be trusted who is ignorant of astronomy. Galen, following Hippocrates, maintained the same opinion, especially of the influence of the moon. Hence in diseases the lunar periods were said to correspond with the succession of the sufferings of the patients. The critical days or crises (as they were afterwards called), were the seventh, fourteenth, and twenty-first of the disease, corresponding to the intervals between the moon's principal phases. While the doctrine of alchymists prevailed, the human body was considered as a microcosm ; the heart, representing the vital principle, was placed under the influence of the sun ; the brain was regulated and controlled by the moon. The planets had each its proper influence ; Jupiter presided over the lungs, Mars over the liver, Saturn over the spleen, Venus over the kidneys, and Mercury over the organs of gene- ration. Of these grotesque notions there is now no relic, except the term lunacy, which still designates unsoundness of mind. But even this term may in some degree be said to be banished from the terminology of medicine, and it has taken refuge in that receptacle of all antiquated absurdities of phraseology the law. Lunatic, we believe, is still the term for the subject who is incapable of managing his own affairs. Although the ancient faith in the connexion between the phases of the moon and the phenomena of insanity appears in a great degree to be abandoned, yet it is not altogether without its votaries ; nor have we been able to ascertain that any series of observations conducted on scientific principles, has ever been made on the phenomena of insanity, with a view to disprove this connexion. We have even met with intelligent and well- educated physicians who still maintain that the paroxysms of insane patients are more violent when the moon is full than at other times. 124 PHYSIOLOGICAL EFFECTS. Mathiolus Faber gives an instance of a maniac who at the very moment of an eclipse of the moon, became furious, seized upon a sword, and fell upon every one around him. Since it was observed that as the day of the eclipse approached, the patient became more and more sombre and melancholy, it may be inferred that iu this case imagination, excited by the apprehension of the approaching phenomenon, had more to do with the paroxysm than the moon. Ramazzini relates that, in the epidemic fever which spread over Italy in the year 1693, patients died in an unusual number on the 21st of January, at the moment of a lunar eclipse. Without disputing this fact (to ascertain which, however, it would be'necessary to have statistical returns of the daily deaths), it may be objected that the patients who thus died in such numbers at the moment of the eclipse, might have had their imaginations highly excited, and their fears wrought upon by the approach of that event, if popular opinion invested it with danger. That such an impression was not unlikely to prevail is evident from the facts which have been recorded. At no very distant period from that time, in August, 1654, it is related that patients in considerable numbers were by order of the physicians shut up in chambers well closed, warmed, and perfumed, with a view to escape the injurious influence of the solar eclipse, which happened at that time ; and such was the consternation of persons of all classes, that the numbers who flocked to confession were so great, that the ecclesiastics found it impossible to administer that rite. An amusing anecdote is related of a village curate near Paris, who, with a view to ease the minds of his flock, and to gain the necessary time to get through his business, seriously assured them that the eclipse was postponed for a fortnight. Two of the most remarkable examples recorded of the supposed influence of the moon on the human body, are those of Vallis- nieri and Bacon. Vallisnieri declares that being at Padua recovering from a tedious illness, he suffered on the 12th of May, 1706, during the eclipse of the sun, unusual weakness and shivering. Lunar eclipses never happened without making Bacon faint ; and he did not recover his senses till the moon recovered her light. ' That these two striking examples should be admitted in proof of the existence of lunar influence, it would be necessary, says M. Arago, to establish the fact that feebleness and pusil- lanimity of character are never connected with high qualities of mind. Menuret considers that cutaneous maladies have a manifest 125 LUNAR INFLUENCES. connexion with the lunar phases. He says that he himself observed in the year 1760, a patient afflicted with a scald head (teigne), who, during the decline of the moon, suffered from a gradual increase of the malady, which continued until the epoch of the new moon, when it had covered the face and breast, and produced insufferable itching. As the moon increased, these symptoms disappeared by degrees ; the face became free from the eruption ; but the same effects were reproduced after the full of the moon. These periods of the disease continued for three months. Menuret also stated that he witnessed a similar correspondence between the lunar phases and the distemper of the itch ; but the circumstances were the reverse of those in the former case ; the malady attaining its maximum at the full of the moon, and its minimum at the new moon. Without disputing the accuracy of these statements, or throwing any suspicion on the good faith of the physician who has made them, we may observe that such facts prove nothing except the fortuitous coincidence. If the relation of cause and effect had existed between the lunar phases and the phenomena of these distempers, the same cause would have continued to produce the same effect in like circumstances ; and we should not be left to depend for the proof of lunar influence on the statements of isolated cases, occurring under the observation of a physician who was himself a believer. Maurice Hoffman relates a case which came under his own practice, of a young woman, the daughter of an epileptic patient. The abdomen of this girl became inflated every month as the moon increased, and regularly resumed its natural form with the decline of the moon. Now, if this statement of Hoffman were accompanied by all the necessary details, and if, also, we were assured that this strange effect continued to be produced for any considerable length of time, the relation of cause and effect between the phases of the moon and the malady of the girl could not legiti- mately be denied ; but receiving the statement in so vague a form, and not being assured that the effect continued to be produced beyond a few months, the legitimate conclusion at which we must arrive is, that this is another example of for- tuitous coincidence, and may be classed with the fulfilment of dreams, prodigies, &c., &c. As may naturally be expected, nervous diseases are those which have presented the most frequent indications of a relation with the lunar phases. The celebrated Mead was a strong believer, not only in the lunar influence, but in the influence of 12ti DIFFICULTY OF DISPROVING. all the heavenly bodies on all the human. He cites the case of a child who always went into convulsions at the moment of full moon. Pyson, another believer, cites another case of a paralytic patient whose disease was brought on by the new moon. Menuret records the case of an epileptic patient whose fits returned with the full moon. The transactions of learned societies abound with examples of giddiness, malignant fever, somnambulism, &c., having in their paroxysms more or less corresponded with the lunar phases. Gall states, as a matter having fallen under his own observation, that patients suffering under weakness of intellect, had two periods in the month of peculiar excitement ; and in a work published in London so recently as 1829, we are assured that these epochs are between the new and full moon. 13. Against all these instances of the supposed effect of lunar influence, we have little direct proof to offer. To establish a negative is not easy. Yet it were to be wished that in some of our great asylums for insane patients, a register should be pre- served of the exact times of the access of all the remarkable paroxysms ; a subsequent comparison of this with the age of the moon at the time of their occurrence would furnish the ground for legitimate and safe conclusions. We are not aware of any scientific physician who has expressly directed his attention to this subject, except Dr. Olbers of Bremen, celebrated for his discovery of the planets Pallas and Vesta. He states that in the course of a long medical practice, he was never able to discover the slightest trace of any connexion between the phe- nomena of disease and the phases of the moon. In the spirit of true philosophy, M. Arago, nevertheless, recommends caution in deciding against this influence. The nervous system, says he, is in many instances an instrument infinitely more delicate than the most subtle apparatus of modern physics. Who does not know that the olfactory nerves inform us of the presence ot odoriferous matter in air, the traces of which the most refined physical analysis would fail to detect ? The mechanism of the eye is highly affected by that lunar light which, even condensed with all the power of the largest burning lenses, fails to affect by its heat the most susceptible thermometers, or, by its chemical influence, the chloride of silver ; yet a small portion of this light introduced through a pin-hole will be sufficient to produce an instantaneous contraction of the pupil ; nevertheless the integu- ments of this membrane, so sensible to light, appear to be com- pletely inert when otherwise affected. The pupil remains unmoved, whether we scrape it with the point of a needle, moisten it with liquid acids, or impart to its Surface electric 127 LUNAR INFLUENCES. sparks. The retina itself, which sympathises with the pupil, is insensible to the influence of the most active mechanical agents. Phenomena so mysterious should teach us with what reserve we should reason on analogies drawn from experiments made upon inanimate substances, to the far different and more difficult case of organised matter endowed with life. 14. In conclusion, then, it appears that of all the various influences popularly supposed to be exerted on the surface of the earth, few have any foundation in fact. 123 METEOR OF 1STH OF AUGUST, 1783, AS SEEN FROM WINDSOR. THE TWO LOWER FIGURES REPRESENT IT A FEW SECONDS BEFORE ITS EXPLOSION. METEORIC STONES & SHOOTING STARS. CHAPTEE I. 1. Necessity of following out the true spirit of the inductive philosophy in the investigation of physical phenomena. 2. Circumstances attending appearance of meteorites supplied by past observation Ball-lightning Explosive clouds Chladni's catalogue of meteoric stones. 3. Remark- able falls of aerolites. 4. Physical condition and analysis of aerolites. 5. Crust of meteorites, their internal mass. 6. Their magnitude and velocity. 7. The different hypotheses or theories proposed to explain them. 8. Luminous appearance explained. 9. Hypothesis of Poissoc. 10. Atmospheric origin impossible. 11. Volcanic origin inadmis- sible. 12. Lunar origin rejected. 13. Planetary origin generally admitted. 14. Remarkable appearances of shooting-stars recorded in history. 15. Shower of stars seen in 1788 and 1799. 16. Also in 1822 and 1831. 17. Remarkable shower in 1833. 18. Vast number of shooting-stars seen on that occasion. 19. Their magnitude. 1. WHEN we reflect upon the length of time which has elapsed since just methods of investigating nature were first formally taught by BACON, we cannot fail to be struck with surprise at witnessing the frequency with which these inestimable precepts LAKDNER'S MUSEUM OF SCIENCE. s 129 METEORIC STONES AND SHOOTING STARS. are neglected and overlooked. There appears to be a disposition inherent in the mind springing probably from that arrogance and vanity, which are invariably the offspring of ignorance that induces us precipitately to rush to the formation of theories and the assumption of causes, omitting or postponing the far more important though less ambitious duty of analysing phenomena. It is true that these observations are less applicable to that order of minds which have been disciplined in the severe schools of the old and long-established universities, where the works of BACON, and the mathematical classics of NEWTON and LAPLACE, are studied with a zeal and perseverance which do not fail to infuse their spirit into the minds of their aspiring successors. But in the much larger class of half-disciplined or self-taught aspirants to scientific rank, the disposition we refer to frequently exists, and to a proportionate extent retards their progress, and impairs the value of their labours. The public teacher should, therefore, omit no proper oppor- tunity of inculcating the true spirit of the inductive philosophy, which, in our day, has afforded so rich a harvest of discovery. We shall avail ourselves of the opportunity which the con- sideration of aerolites offers, to give an example of the rigorous observance of the canons of Bacon's philosophy in the investi- gation ol nature. Every one possessed of the smallest amount of the current information of the day, imagines that he knows what meteoric stones are. He knows that they fall from the air, and that they are accompanied by fire and noise. With this amount of infor- mation he unhesitatingly sets about to conjecture their origin, and to get up a theory to explain them. As might be expected, the theory produced under such circumstances is always crude and absurd, and falls to pieces upon the slightest comparison with the phenomena. When any new and unexplained phenomenon offers itself to our inquiry, the first duty of the investigator is to inform himself, with the most scrupulous accuracy, of all the circumstances, however minute, which accompany it ; and if past observation cannot answer all circumstantial inquiries which his under- standing may suggest as necessary, he must patiently wait the recurrence of a like phenomenon, and diligently observe it. When he shall have thus collected all the circumstances that can be imagined to throw light on its origin, he will then, and not until then, be in a condition to justify an inquiry into its cause. 2. Let us see, then, what circumstances attending the appear- ance of meteorites past observation has supplied. 130 APPEARANCES OP AEROLITES. These meteors manifest themselves in various ways. Their fall is often preceded by the appearance of a stream of light passing with great velocity across a part of the firmament more or less extensive, which terminates with an explosion, sometimes so loud, that windows and doors, and even buildings themselves, are shaken by it as if by an earthquake. This phenomenon is sometimes called ball-lightning, a term which is liable to the objection that it implies an analogy, or identity of origin, between these meteors and common lightning, which not only is not proved, but is attended with no probability. Sometimes a small and dark cloud is observed to be suddenly formed in a perfectly clear sky, which explodes with a noise resembling a succession of discharges of artillery, and stones are hurled from it in a shower. Such a cloud moving over an extensive tract of country has sometimes thrown- down thousands of meteoric stones of various, magnitudes, but alike in their constituents and external appearance. The luminous appearance and subsequent explosion attending these meteors were long known ; the fact, however, that heavy substances, now called meteoric stones, were projected upon the surface of the earth at the same time, was not- clearly proved or generally admitted until the present century. Abundant evi- dence, however, has been supplied, by the vigilance and zeal of contemporaneous philosophers, of the reality of these deposits. Chladni, in his work on this subject, has given an extensive chronological catalogue of the meteoric stones, which supplies examples of these phenomena occurring in various parts of the world several times in each year of the last century. 3. Remarkable falls of aerolites were observed at Barbotan, in the department of the Landes, in France, on the 24th July, 1790 ; at Sienna, in Italy, on the 16th June, 1794 ; at Weston, in Connecticut, U. S., on the 14th December, 1807 ; and at Juvenas, in the department of Ardche, in France, on the loth June, 1821. The phenomenon sometimes occurs under a perfectly clear and unclouded sky. On the 16th September, 1843, a large aerolite fell at Kleinwenden, near Mulhausen, attended with a thundering noise, the sky being at the time entirely free from clouds. The fact, then, may be regarded as conclusively established, that masses of stony matter, of various magnitudes, and often of very considerable weight, are frequently seen passing athwart the heavens, with great apparent velocity, which are afterwards precipitated upon the earth with extraordinary force. K 2 131 METEORIC STONES AND SHOOTING STARS. The second circumstance worthy of attention is, that these bodies rarely strike the surface of the earth in a direction either vertical or nearly so. They generally come in a direction very oblique to the plane of the horizon. It may be asked, how the direction in which they strike the earth can be ascertained unless they are seen, which rarely happens, at the moment of their fall. Their direction is rendered manifest by the manner in which they penetrate the surface of the ground which they always do, and to a depth more or less considerable. The velocity of their motion when they encounter the earth is another circumstance of much importance. This velocity is discoverable by observation on their movement while visible, as well as by inferring the force with which they struck the ground from the depth to which they penetrate it. It is accordingly found by means of such observations that their velocities belong to the kind of motions which characterise the bodies of the solar system, and such as are never witnessed in the motions of terrestrial bodies. They are velocities which could not be imagined to be imparted by the earth's gravitation to any masses attracted from points within the limits of the atmosphere. 4. On examining the physical condition, and analysing the constituents of the masses thus precipitated, several circum- stances worthy of notice are presented. In whatever way they fall, whether from fire-balls visible at night, from a cloud in the day, or from a clear and serene sky, they exhibit a general and striking resemblance in their form, their external crust, and their constituents. When recently fallen, they have always a temperature more or less elevated. They exhibit a shining black and apparently burnt surface, and their con- stituents are generally iron, nickel, cobalt, manganese, chromium, copper, arsenic, tin, potash, soda, sulphur, phosphorus, and carbon, being in all about a third of the elementary substances to which terrestrial bodies have been reduced by chemical analysis. These constituents are found with some exceptions to be the same at whatever epochs and at whatever parts of the earth these bodies may have fallen. It is important to observe here, that the iron and nickel are almost always in the metallic form a state in which they are never known to exist naturally on the surface of the earth. These metals, when found in the earth, are invariably combined with oxygen, and it is their oxydes only which have a place among natural terrestrial substances. The iron and nickel used in the arts are obtained by the decomposition of the ores in the processes of metallurgy. 132 CONSTITUENTS OP AEROLITES. In some exceptional cases the iron contained in these masses differs extremely in its proportion and quality. The meteorites which fell at Agram, in India those which were found at Sisim, in the Jeniseisk government and those brought by Humboldt from Mexico, contained so much as 96 per cent, of very malleable iron, while the aerolite of Sienna did not contain above 2 per cent., and those of Jonzac and Juvenas contained no metallic iron at all. 5. The crust by which meteorites are almost invariably invested is only a few hundredths of an inch in thickness, and is described by Humboldt as being highly characteristic. It has often a pitchy lustre, and is sometimes veined. This black crust is separated from the light gray mass within it by a line as sharply denned as that of the dark leaden-coloured crust of the white granite blocks brought by Humboldt from the cataracts of the Orinoco, and which are also found by the side of many cataracts in other parts of the world, as those of the Nile and the Congo. It is observed by Humboldt that the greatest heat of porcelain furnaces can produce nothing similar to the crust of the aerolites, so distinctly and sharply separated from the unaltered mass within. Appearances which might seem to indicate a softening of the fragments have been occasionally recognised, but in general the condition of the greater part of the mass the absence of all flattening which might be pro- duced by the fall and the moderate degree of heat perceived on touching the newly-fallen aerolite, are far from indicating a state of internal fusion during its rapid passage through the atmosphere. 6. Observations and measurements made on the magnitude and velocity of these meteoric bodies supply many surprising results. Fire-balls have been observed whose computed diameters vary from 500 to 2,600 feet. The fire-ball seen at Weston, in Con- necticut, U.S., on the 14th December, 1807, measured 500 feet. Le Eoi observed one on the 10th July, 1771, which measured about 1000 feet ; and Sir Charles Blagden estimated the diameter of one observed by him on the 18th January, 1713, at 2,600 feet. These measurements include, however, not only the solid mass, but the igneous matter by which it may have been surrounded. Of the meteoric masses found on the surface of the earth, the largest known are those of Bahia in Brazil, and of Otumpa, described by Kuben de Celis. These are from seven to seven and a half feet in diameter. The meteoric stone of ^Egos JPotamos, celebrated in antiquity, mentioned in the " Chronicle of 133 METEOKIC STONES AND SHOOTING STARS. the Parian Marbles," and which fell about the year of the birth of Socrates, has been described as being of the size of two mill-stones, and equal in weight to a full waggon load. In the beginning of the tenth century an enormous meteoric mass fell into the river near Narni, the magnitude of which was so great, that when resting on the bottom, it projected four feet above the surface. According to a popular tradition in Mongol, there is, in a plain near the sources of the Yellow River in Western China, a fragment of black rock forty feet high, which fell from heaven. It is observed by Humboldt, that great as these masses are they can only be regarded as fragments of the mass which exploded in the fire-ball, or was hurled from the cloud. The heights at which these objects have been visible, and the actual velocities of their motion, will be presently noticed. 7. Such are the circumstances attending the exhibition of these meteors, which have been collected from careful and accurate information. Let us now turn our attention to the different methods by which it has been attempted to explain them. Four different hypotheses, or theories, have been proposed for this purpose. First. It is supposed that the matter composing them has been drawn up from the surface of the earth in a state of infinitely minute subdivision, as vapour is drawn from liquids ; that, being collected in clouds in the higher regions of the atmosphere, it is there agglomerated and consolidated in masses, and falls by its gravity to the surface of the earth ; being occa- sionally drawn from the vertical direction which would be imparted to it by gravity, by the effect of atmospheric currents and thus occasionally striking the earth obliquely. We shall call this the atmospheric hypothesis. Secondly. It is supposed that meteoric stones are ejected from volcanoes, with sufficient force to carry them to great elevations in the atmosphere, in falling from which they acquire the velocity and force with which they strike the earth. The oblique direction with which they strike the ground is explained by the supposition that they may be projected from the volcanoes at corresponding obliquities, and that, by the principles of pro- jectiles, they must strike the earth at nearly the same inclination as that with which they have been ejected. This we shall call the volcanic hypothesis. Thirdly. It has been suggested that meteorites may be bodies which have been ejected from lunar volcanoes, with such a force that they may have departed from the moon to a distance so great, as to come within such a distance of the earth, that the 134 PROPOSED EXPLANATIONS OP THEM. terrestrial attraction exerted upon them predominating over that of the moon, they may have either fallen down directly upon the earth, or may have revolved round it in a curvilinear orbit, with a motion constantly retarded by the earth's atmo- sphere, the consequence of which would be that they would continually approach the earth, and at length fall upon its surface. We shall call this the lunar hypothesis. Fourthly. It has been supposed that meteo'rites are planetary bodies ; that they revolve in orbits round the sun ; that these orbits intersect the annual path of the earth ; that when the earth passes through the point of intersection of its path with their orbits they either encounter it directly, and fall upon its surface, or entering its atmosphere, are rapidly retarded by the resistance of that fluid, and are then drawn to the surface by the terrestrial attraction. To render this supposition sufficient to explain the large numbers of meteorites which sometimes appear simultaneously and fall down upon the surface, it is assumed that these planetary bodies circulate round the sun in groups consisting of numerous individuals which move together with equal, or nearly equal, velocities in parallel paths, thus maintaining for long periods of time their relative position, and passing through the celestial space like a flock of gregarious birds. Now, if we suppose the parallel paths of a number of such bodies to be represented at A A, (fig. 7), and that the earth's path, E E', passes across them, it is clear that it, while the earth is passing from e to e', these bodies happen to be at that point of their orbit, an encounter must ensue, and they must, in greater or less number, pass 135 METEORIC STONES AND SHOOTING STARS. through the terrestrial atmosphere and be drawn down upon the surface by the earth's attraction. By admitting the possible existence of a swarm of such bodies consisting of many hundreds, or even thousands, against which there is no physical impossibility, not to say improbability, a satisfactory explanation is afforded of the most extraordinary phenomena of meteoric showers that have ever been witnessed or recorded. 8. Such are the various theories which have been offered to explain the phenomena attending meteoric stones and shooting stars. The evolution of light which attends their rapid progress through space has been accounted for in all of them in the same manner. It is supposed that, in the rapid motion with which the body proceeds, the air which lies in its path is so extremely condensed, as either to become itself luminous, or to acquire so intense a heat as to render the stone incandescent, or, perhaps, to produce upon it a superficial combustion, the signs of which are exhibited in the blackness and elevated temperature of its surface. This reasoning is supported by the well-known experiment of the fire-syringe. In that instrument a solid piston is fitted in a cylinder, so as to be air-tight, carrying a piece of amadou or other easily combustible matter, at its end. When the piston is suddenly forced down, so as to produce an instantaneous and severe compression of the air under it, the amadou takes fire, and, if the cylinder be glass, a flash of light is visible through it. It has therefore been contended, that in this experiment the air under the piston has acquired, by compression, such a temperature as renders it luminous. More recent experiments, however, made in France, throw doubt upon the validity of this inference. It is said that the unctuous matter commonly used to lubricate the piston in the fire-syringe is, in fact, the source of the ignition ; for that, when experiments were made with pistons not so lubricated, the flash of light was not produced. It is, therefore, considered not to be satisfactorily proved, that air by such mechanical compression has become luminous. Still, however, it may be contended that, even though the air were not to become luminous, it may, nevertheless, be raised to such a temperature by com- pression as, by contact with the meteorite, may render the latter luminous. Admitting the possibility of this supposition, as applied to the air contiguous to the earth, or at any moderate elevation, a difficulty has been raised from the vast height at which meteorites have been visible. By barometric experiments and observations 136 LUMINOUS APPEARANCE EXPLAINED. made on the duration of the morning and evening twilight, it may be considered as proved, that beyond the elevation of thirty miles there exists no atmosphere possessing any sensible mechanical properties. We may safely conclude that at such elevations the air must be so infinitely attenuated as to be divested of all sensible resistance or inertia. The space there must, for example, be more nearly a vacuum than any which could be produced under the receiver of the most perfect air-pump ; how, then, can we imagine such a compression of air so rarefied to be produced, as would be necessary to evolve the enormous temperature requi- site to render luminous the matter composing meteoric stones 1 To this objection the following very plausible answer has been made. It is known that the quantity of latent heat contained in any proposed volume of air is greater the more rare and attenuated the air is. This is easily proved. Every one knows that when a volume of air at a given temperature expands into a larger volume, its temperature falls, although no heat has been abstracted from it. Since, therefore, it contains the same absolute quantity of heat as it did before it expanded, and since, nevertheless, its sensible heat is less, as is proved by its fall of temperature, it follows that the portion of sensible heat which has disappeared must have become latent, that is to say, the air has augmented its latent at the expense of its sensible heat. Since then highly rarefied air contains much more latent heat than air of greater density, and since this excess of latent heat is greater and greater as the rarefaction is greater and greater, it follows that the latent heat of the air in the highest strata of the atmosphere must be immeasurably greater than in the inferior strata, and that the same degree of sudden compression applied to it would develop a much greater amount of this latent heat, and consequently produce a much greater elevation of temperature than in the lower regions. It is, therefore, contended that not only notwithstanding the rarefaction of the air in the higher strata, but' 'because of that rarefaction, a meteorite rushing through it with a planetary velocity, would, by the sudden compression of the air driven before it, produce an elevation of temperature sufficient not only to cause a superficial combustion of the meteorite, but to cause its explosion by the sudden expansion and combustion of any volatile or combustible matter which might form part of its constituents. 9. There is yet another supposition extremely plausible and ingenious which was suggested by Poisson, the eminent French geometer, to explain the evolution of light and heat observed 137 METEORIC STONES AND SHOOTING STARS. in the passage of areolites through the firmament. He affirmed the probability of an atmosphere of electricity surrounding the earth and lying above the atmosphere of air. He supposed that the meteorite rushing through this electric atmosphere would decompose the electric fluid exactly as the friction of an electric machine decomposes it between the cushion and the glass, and that by such electric decomposition light and heat would be evolved. It may then be admitted that all of the hypotheses above mentioned will equally afford an explanation of the evolution of light and heat ; and that, on the other hand, so far as regards these effects, all the hypotheses are subject to the same objections and the same difficulties. Let us, however, examine them severally, and see how far in other respects they will supply an explanation of the phenomena. 10. The atmospheric hypothesis is subject to objections so unanswerable, that it may be considered as altogether set aside. In order to suppose it probable that aerolites could be formed in the atmosphere, we must show that their constituent elements can exist there. We know that hail and snow can be formed in the air, because it can be proved that aqueous vapour is sus- pended there, and that a temperature is sometimes produced there so low as to convert that vapour, first, into the liquid, and then into the solid form of snow or hail. But the most rigorous analysis has never detected in the atmosphere any of the con- stituents of meteoric stones, nor is there any proof that the constituent principles of the air could dissolve, evaporate, or sublimate such substances. Nor can it be said that, although the atmosphere which immediately surrounds us may not have such properties, yet, that at the great elevations in which meteorites are formed, the air may consist of different con- stituents ; for, besides the fact that it has been ascertained by direct analysis that the atmosphere, at all elevations to which man has ever yet attained, consists of exactly the same con- stituents, in exactly the same proportions, there is a general law, which prevails among all gaseous substances, that when different gases are superposed they will, notwithstanding their different degrees of levity, ultimately mingle so as to form a uniform mass ; thus, if we could imagine for a moment a stratum of air to exist near the top of the atmosphere, having constituents different from those around us, such stratum would gradually intermingle with the strata below it, until the whole would acquire a uniform quality. It is, therefore, physically impossible that there can exist in any elevated region of the air any .138 NOT OF TERRESTRIAL ORIGIN. substances capable of discharging or sublimating the matter of meteoric stones. To these objections we may add others. Although it may be admitted, as Arago argues, that the constituent principles of aerolites should really exist in the atmosphere, and that they only escape analysis because of their extreme minuteness, it would still be necessary to explain with such feeble and such dispersed elements a sudden precipitation, yielding stones of several hundred weight, such as those preserved at Ensen- heim, in Alsace, or 3000 or 4000 stones of various dimensions, like those which were separated and shot off by the 1'Aigle meteor, which we shall presently notice. It would be necessary to assign the cause that combines the scattered molecules, and forms them into a single mass. It is not affinity, for the elements composing aerolites are not generally in a state of combination, but simply agglomerated and held together in juxta-position. And yet, if they are not subjected to any mutually attractive force, these little globules ought to fall separately as they are formed. It is in vain to object that they might be suspended, for a greater or less time, by a cause analogous to that which, according to the ingenious hypothesis of Volta, balances the particles of hail between two clouds, so as to give them time to enlarge by the addition of new layers of ice. The fact still remains, that these latter have never been seen to amount to several hundred weight, though the elements that form hail are much more abundant in the air than those of which aerolites are supposed to be formed. Besides, in Yolta's theory, the suspension of hail in the atmosphere is attributed to the reciprocal action of electric clouds, a cause which cannot be in like manner adapted to the formation of aerolites, since the meteors that carry them sometimes burst in the clearest weather. But even granting all this, and admitting the formation of aerolites in the atmosphere by some unknown agency, how shall we account for the circumstances attending their collision with the surface of the earth ? According to this theory, they would move to the surface of the earth by the operation of terrestrial gravity alone, and would meet the earth with a velocity due to the height from which they fell. Now the actual velocities with which they are known to strike the earth could never be acquired under the mere agency of terrestrial gravity, through any height within the ordinary limits of the air. But if the velocity of the meteorites be incompatible with this theory, their direction is still more so. Their obliquity could never be produced by any conceivable atmospheric current. 139 METEORIC STONES AND SHOOTING STARS. We may, therefore, safely pronounce the atmospheric theory to be incompatible with the ascertained circumstances of the phenomena, and to require admissions inconsistent with the established principles of physics. 11. The volcanic theory is subject to objections as decisive. The nature of the substances ejected from terrestrial volcanoes is well known, and we do not find among them the substances which form the constituents of meteorites ; besides this, it is found that meteoric stones fall on parts of the earth so remote from volcanoes, and at times so distant from any known extensive eruptions, that it is impossible to admit the sup- position that they have proceeded from this cause. For these and other reasons, needless to dwell on, the volcanic hypothesis is set aside. 12. The lunar hypothesis has been seriously entertained by many of the most eminent geometers of the last century. Chladni states that the possibility of such an origin of the aerolites was first suggested by Paolo Maria Terzago, an Italian philosopher, in 1660. Unaware of this ancient conjecture, the hypothesis was revived by Dr. Olbers on the occasion of the great fall of meteorites at Sienna, on the 16th of June, 1794. That astronomer in the following year undertook to investigate the force with which such bodies should be projected from a lunar crater, in order to enable them to pass from the sphere of the moon's attraction into that of the earth. The same problem subsequently engaged the attention of Laplace, Biot, Brandes, and Poisson for many years. It was then supposed that, notwithstanding the absence of air and water, active lunar volcanoes existed. Some countenance to this idea was derived from a remarkable phenomenon, which several observers affirmed that they had witnessed on the dark disc of the moon in lunar eclipses. They saw, or imagined they saw, vividly bright luminous spots at distances not inconsiderable within the moon's limb. Now such appearances, if real, could only be explained by active lunar volcanoes, or by the very improbable supposition of the existence of holes through the moon through which the sun's light passed. The supposition of any such origin as an aurora borealis was removed by the admitted absence of an atmosphere. Laplace, Biot, and Poisson, agreed in their calculations of the velocity with which such bodies must be projected from the moon to reach the earth. This velocity would be about 8000 feet per second. But Olbers showed, that although such a force of projection might bring them to the earth, it would not impart to them, on arriving there, a speed greater than 35,000 feet per 140 THEIR OPJGItf PLANETARY. second, a velocity three or four times less than that with which meteorites have been ascertained to strike the ground. Laplace, though not without much doubt, inclined rather to the lunar than the planetary hypothesis. But at that time the prodigious velocity with which aerolites traverse the terrestrial atmosphere was not so well ascertained as it has been more recently. In fine, the consideration of these great velocities, combined with the great improbability of the existence of active volcanoes on the moon, an improbability which has been greatly increased if indeed it be not converted into an impossibility by the exten- sive selenographic researches and observations of Messrs. Beer and Madler, has decided the opinion of the scientific world on this long-vexed questioD, and the lunar hypothesis like the others has been by common consent set aside. 13. It is, then, agreed generally, that the planetary hypothesis must be taken as the true solution of the problem of the aerolites. Taking it then to be established on satisfactory grounds that aerolites are planetary bodies which the earth encounters in its annual course round the sun, it remains to examine more closely the peculiar circumstances which have attended their appearance, so as to obtain some more exact and special knowledge of them. We shall at once assume, what in the sequel will be abundantly evident, the identity of these bodies with shooting stars. Among the numerous records, ancient and modern, of remarkable exhibitions of these objects, we select the following as worthy of attention. 14. According to Arabian historians, on the night of the death of King Ibrahim-ben- Ahmed, in October, 902, a great fall of shooting stars took place, which were described as resembling " a rain of fire." On the night of 25th April 1095, it was recorded that in France the stars were seen " falling from heaven as thick as hail" by innumerable witnesses, and the terrific phenomenon was men- tioned at the Council of Clermont as foreboding the great movement in Christendom. On 19th October, 1202, stars were recorded as falling during the whole night like a " shower of locusts." In the " Chronicon Ecclesise Pragensis," page 389, it is re- oorded that on 21st October, O. S., 1366, for several hours during the morning, stars were seen continually falling in such numbers that no person could count them. 15. Humboldt relates that a friend of his accustomed to exact 141 METEOEIC STONES AND SHOOTING STAES. trigonometrical measurements, saw, in 1788, at Papayana, a town situate in 2 26' N. lat., and at an elevation of 5,880 feet, at noon- day, with the sun shining brightly in an unclouded sky, his whole room illuminated by a ball of fire. He was standing at the moment with his back to the window, and, on turning round, a great part of the track left by the meteor was still visible and brilliantly marked. After midnight, on 12th November, 1799, Humboldt and Bonpland saw a prodigious shower of shooting stars at Cumana. This phenomenon was not local, being seen over a great part of the earth. 16. On the night 12th November, 1822, shooting stars, mingled with balls of fire, were seen in vast numbers at Potsdam by Kloden, On the night of 13th November, 1831, Captain Berard, of the French navy, commanding the brig Le Loiret, off the Spanish coast near Carthagena del Levante, saw in a perfectly cloudless sky, at four in the morning, a considerable number of shooting stars and luminous meteors of great dimensions. During more than three hours they continued to shoot at the average rate of three per minute, and consequently 540 must have appeared in that interval. One of these meteors which passed through the zenith was especially remarkable, exhibiting a luminous train half the breadth of the moon, in which were plainly distinguished all the colours of the rainbow. This train continued visible during more than six minutes. 17. One of the most interesting descriptions of these phenomena is that published by D. Olmsted of Newhaven, Massachusetts, U.S., in which a detailed account is given of the magnificent showers of stars which took place in the United States on the night of 12-13th November, 1833. The meteors began to attract notice by their frequency as early as 9 o'clock on the evening of 12 Nov., the exhibi- tion became strikingly brilliant about 11 o'clock, but most splendid of all about 4 o'clock, and continued with but little intermission until darkness merged in the light of day. A few large fire-balls were seen even after the sun had risen. The entire extent of the exhibition is not ascertained, but it covered no inconsiderable portion of the earth's surface. It has been traced from the longitude of 61 in the Atlantic ocean, to longitude of 100 in central Mexico, and from the North American lakes to the southern side of the island of Jamaica. Everywhere within these limits, the first appearance was that of fire-works of the most imposing grandeur, covering the entire vault of heaven with myriads of fire-balls resembling sky-rockets. 142 REMARKABLE SHOWERS OF STARS. On more attentive inspection, it was seen that the meteors exhibited three distinct varieties ; the first consisting of phos- phoric lines, apparently described by a point ; the second of large fire-batts, that at intervals darted along the sky, leaving numerous trains, which occasionally remained in view for a number of minutes, and in some cases for half an hour or more ; the third, of undefined, luminous bodies, which remained nearly stationary for a long time. One of the most remarkable circumstances attending this display was, that the meteors all seemed to emanate from one and the same point. They set out at different distances from this point, and proceeded with immense velocity, describing, in some instances, an arc of 30 or 40 in less than four seconds. At Poland, on the Ohio, a meteor (of the third variety) was distinctly visible in the north-east for more than an hour. At Charleston, South Carolina, another of extraordinary size was seen to course the heavens for a great length of time, and then was heard to explode with the noise of a cannon. The point from which the meteors seemed to emanate, was observed by those who fixed its position among the stars to be in the constellation Leo ; and what is very remarkable, this point was stationary among the stars during the whole period of observation ; that is to say, it did not move along with the earth in its diurnal rotation eastward, but accompanied the stars in their apparent progress westward. It is not certain whether the meteors were in general accompanied by any peculiar sound. A few observers reported that they heard a hissing noise, like the rushing of a sky-rocket, and slight explosions, like the bursting of the same bodies. Nor does it appear that any substance reached the ground which could be clearly established to be a residuum or deposit from the meteors. 18. Attempts were made to obtain at least some approximation to the number of shooting stars which appeared on this occasion. At the time when they were presented in the greatest number, an observer at Boston estimated them at about half the number of the flakes which would be presented by a dense snow-storm. "When they became considerably less dense, so as to allow being distinctly observed, he counted in a vertical zone having the breadth of 36 of azimuth, 650 in fifteen minutes ; but he estimated this as not above two-thirds of the total number which actually appeared in that interval, so that the total number would have been 1000, and supposing them to prevail uniformly throughout the entire hemisphere, the number exhibited every quarter of an hour would be 10,000, being at the rate of 40,000 per hour, and as the phenomenon 143 METEOKIC STONES AND SHOOTING STARS. continued for seven hours, the total number must have greatly exceeded 280,000, inasmuch as this estimate was based on observations when the density of the stars was much less than its maximum. It may, therefore, be inferred that on this memorable night of the 12-13th November, 1833, 300,000 masses forming part of the solar system, and foreign to the earth, passed through that part of the terrestrial atmosphere, which was visible at Boston. 19. From the apparent magnitude of many of the meteors, and their probable distance, it was conjectured that they were bodies of a very large size, although it was impossible to ascertain their magnitude with any certainty. It was supposed that they were only stopped in the atmosphere, and prevented from reaching the earth by transferring their motion to columns of air, large volumes of which they would suddenly and violently displace. It was remarked that the state of the weather, and the condition of the seasons following this meteoric shower, were just such as might have been anticipated from these disturbing circumstances of the atmospheric equilibrium. Such were the speculations to which this remarkable phenomenon gave rise. 144 JIETEOR OF THE EVENING OF SUNDAY, NOV. 13, 1803. SMALLER BALLS TINGED WITH YELLOW, ORANGK, AND PURPLE. ABOUT A SECOND AND A HALF PREVIOUS TO ITS DISAPPEARANCE IT ASSUMED THE SHAPE OF AN EGG. Phil. Mag., Vol. XVii. METEORIC STONES & SHOOTING STARS. CHAPTEE II. 1. Encke's calculation of the direction of the shooting-stars seen from 1833 to 1838. 2. Apparent magnitudes of those objects. 3. The luminous train which follows them not an optical illusion. 4. Hypotheses to explain them. 5. Heights, directions, and velocity of shooting-stars, calculated by Brandes. 6. A like calculation by Quetelet. 7. A like calculation by Wartmann. 8. Shooting-stars and fire-balls identical. 9. Lunar origin rejected. 10. Eeceived explanation of the pheno- mena. 11. Difficulties and objections. 12. Description of great shower of stars witnessed in 1799 by Humboldt and Bonpland. 13. Description of like showers in 1833-40. 14. August meteors. 15. Halley suggests the use of these meteors to determine the longitude. 16. Table of shooting-stars from 763 to 1837. 17. Infer- ences from this. 18. Observation of Sir J. Herschel in 1836. 19. Of Wartmann in 1837. 20. Of Tharand in 1832. 21. Annual epochs of the prevalence of these meteors. 22. "Why those masses are not visible like the moon and planets by the reflected light of the sun. 23. Zodiacal light. 24. The nebulous matter producing it may cause shooting-stars. 25. Shooting-stars may become satellites to the earth. 26. M. Petit claims to have discovered one. 27. Sun-stones. LARDXER'S MUSEUM OP SCIENCE. No. 11. 145 METEORIC STONES AND SHOOTING STARS. 1. PROFESSOR ENCKE made a computation founded on the whole collection of observations made on the meteors which appeared in November, 1833, in the United States, over an extent of country included between the latitudes 35 and 42, from which he inferred that all these meteoric bodies had a common direction, and that their motion was exactly contrary to that which the earth had at the moment of their appearance. In the great showers of shooting-stars which were afterwards observed in November, 1834, 1837, and 1838, the same general parallelism of the directions of their motion was ascertained, and as before, they were observed to move from a certain point in the constellation of Leo. A similar parallelism of direction has been observed in the showers of shooting-stars which appear at other times of the year, and it is ascertained that those which reappear in the same month have always the same direction. On the 13th November, 1834, a like shower of shooting-stars was witnessed in North America, but much less considerable in point of numbers. On the 13th November, 1835, a meteorite fell in France in the department De FAin, which set fire to a barn. On the same night a shooting-star, larger and brighter than Jupiter, was seen at Lille. It left behind it a train of sparks like those which issue from a rocket. 2. Whatever be the origin of the phenomena of shooting-stars it cannot fail to be interesting to learn the principal circum- stances which observation has collected respecting them. Their apparent magnitudes are very various. Sometimes they are not brighter or larger than the smallest star visible to the naked eye, and at other times they surpass in splendour the most brilliant of the planets. Sometimes the globular form can be distinctly recognised upon them, and they are not distin- guishable from the meteors called fire-balls. 3. Shooting-stars seem to prevail equally in every climate and in every state of the weather. They are occasionally seen at all seasons of the year, but more frequently in summer or at the end of the autumn. They appear usually to be followed by a luminous train of intensely white light. A question will immediately arise, whether this be a real continued physical line of light, or whether it must not rather be ascribed to the same cause which makes us see a complete circle of light when a lighted stick revolves rapidly in a circle In that case the circle of light is not real, the effect being an optical illusion. The membrane of the eye which is affected by light has been ascertained to preserve the impression made upon 146 LUMINOUS TRAIN OF THESE STARS. it for about one-tenth of a second after the cause which pro- duced that impression has ceased to act. We, consequently, continue to see a visible object in any position for a tenth of a second after it has left that position. If a luminous object move over a certain space in one-tenth of a second, the eye will, therefore, see it at the same time in every part of that space, and consequently that space will appear one continuous line of light. If, then, the luminous train which is visible after a shoot- ing star, extends through a space over which the star has moved in one-tenth of a second, it is then possible that such luminous train may be illusory, being a mere optical effect of the rapid motion of the star. But if it be longer than this, or if it be visible in any one place for more than the tenth of a second after the star has moved from that place, then it cannot be explained on this principle, and must be admitted to be an actual train of light. Now it is stated by observers of these meteors that the trains are sometimes seen for several minutes. In the case of actual fire-balls, Dr. Olbers observed trains which con- tinued visible for six or seven minutes, and Brandes in one instance estimated that fifteen minutes elapsed between the extinction of the fire-ball and the disappearance of the luminous train. Admiral Krusenstern, in a voyage round the world, saw the train of a fire-ball, which continued to shine for the space of an hour after the ball itself had disappeared, during which interval the train appeared almost stationary. In general, the trains have the same hollow, cylindrical appearance as the tails of comets, their inner part appearing to be void of luminous matter, and a further resemblance to comets is exhibited in the curved form, which they sometimes assume. 4. Various and discordant have been the explanations offered of these luminous trains. Some have ascribed them to an oily sulphurous vapour existing in the atmosphere, which, being disposed in thin layers, and becoming inflamed, would exhibit the appearance of a brilliant spark passing rapidly from point to point. Beccaria and Vassali considered them to be lines of electrical sparks ; an hypothesis, however, which has been abandoned. Lavoisier, Volta, and others explained theae meteors, by supposing that hydrogen gas, accumulated, by its lightness, in the higher regions of the atmosphere, was inflamed. But the general law of gases, which gives them a tendency to mingle, notwithstanding the effect of their specific gravities, puts aside this hypothesis. 5. In the year 1798, an investigation of the heights of shooting-stars was undertaken by Brandes, at Leipsig, and Benzenberg, at Dusseldorf. Having selected a base line (about L 2 147 METEORIC STONES AND SHOOTING STARS. nine miles in length), they placed themselves at its extremi- ties, on appointed nights, and observed all the shooting-stars which appeared, tracing their courses through the heavens on a celestial map, and noting the instants of their appearances and extinctions by chronometers previously compared. The difference of the paths traced on the heavens afforded data for the determination of the parallaxes, and consequently the heights and the lengths of the orbits. On six evenings, between Sep- tember and November, the whole number of shooting-stars seen by both observers was 402 : of these, 22 were identified as having been observed by each in such a manner that the altitude of the meteor above the ground at the instant of extinction could be computed. The least of the altitudes was about 6 English miles. Of the whole, there were 7 under 45 miles : 9 between 45 and 90 ; 6 above 90 ; and the highest was above 140 miles. There were only two observed so completely as to afford data for determining the velocity. The first gave 25 miles, and the second from 17 to 21 miles, in a second. The most remarkable result was, that one of them, certainly, was observed not to fall but to move iii a direction away from the earth. By these observations, a precise idea was first obtained of the altitudes, distances, and velocities, of these singular meteors. A similar but more extended plan of observation was organised by Brandes, in 1823, and carried into effect at Breslau and the neighbouring towns, by a considerable number of persons, observing at the same time on concerted nights. Between April and October, about 1800 shooting-stars were noted at the diffe- rent places out of which number 62 were found which had been observed simultaneously at more than one station, in such a manner that their respective altitudes could be determined, and 36 others of which the observations furnished data for estimating the entire orbits. Of these 98, the heights (at the time of extinction) of 4 were computed to be under 15 English miles ; of 15, between 15 and 30 miles ; of 22, between 30 and 45 ; of 33, between 45 and 70 ; of 13, between 70 and 90 ; and of 11, above 90 miles. Of these last, 2 had an altitude of about 140 miles, 1 of 220 miles, 1 of 280, and there was 1 of which the height was estimated to exceed 460 miles. On the 36 computed orbits, in 26 instances the motion was downward, in 1 case horizontal, and in the remaining 9 more or less upward. The velocities were between 18 and 36 miles in a second. The trajectories were frequently not straight lines, but incurvated, sometimes in the horizontal and sometimes in the vertical direction, and sometimes they were of a serpen- tine form. The predominating direction of the motion of the 148 THEIR HEIGHTS AND VELOCITIES. meteors from north-east to south-west, contrary to that of the earth in its orbit, was very remarkable, and is important in reference to their physical theory. 6. A similar set of observations was made in Belgium, in 1834, under the direction of M. Quetelet, the results of which are published in the " Annuaire de Bruxelles for 1837." M. Quetelet was chiefly solicitous to determine the velocity of the meteors. He obtained six corresponding observations, from which this element could be deduced, and the result varied from 10 to 25 English miles in a second. The mean of the six results gave a velocity of nearly 17 miles per second, a little less than that of the earth in its orbit. 7. Another set of corresponding observations was made in Switzerland, on the 10th of August, 1838, a circumstantial account of which is given by M. Wartmann in " Quetelet's Correspondence Mathematique for July, 1839." M. "Wartmann and five other observers, provided with celestial charts, stationed themselves at the observatory of Geneva, and the corresponding observations were made at Planchettes, a village about sixty miles to the north-east of that city. In the space of seven and a half hours, the number of meteors observed by the six observers at Geneva was 381, and during five and a half hours the number observed at Planchettes by two observers, was 104. All the circumstances of the phenomena the place of the apparition and disappearance of each meteor the time it continued visible, its brightness relatively to the fixed stars, whether accompanied with a tram, &c. were carefully noted. The trajectories described by the meteors were very different, varying from 8 to 70 of angular space. The apparent velocities also differed considerably ; but the average velocity was supposed by M. Wartmann to be 25 per second. It was found, from the comparison of the simultaneous observations, that the average height above the ground was about 550 miles ; and hence the relative velocity was computed to be about 240 miles in a second. But as the greater number moved in a direction opposite to that of the earth in its orbit, the relative velocity must be diminished by the earth's velocity (about 19 miles in a second) ; this still leaves upward of 220 miles per second for the absolute velocity of the meteor, which is more than 11 times the orbital velocity of the earth, seven and a half times that of the planet Mercury, and probably greater than that of many of the comets at their perihelion. 8. Such are the principal facts which have yet been estab- lished respecting the heights, velocities, and orbits of the shooting- stars ; and it is from these, chiefly, that we are enabled to form 149 METEORIC STONES AND SHOOTING STARS. any probable conjectures respecting their origin. And since it is now established that no difference is observable between the larger shooting-stars and small fire-balls, both having similar altitudes and velocities, and presenting absolutely the same appearances, we may assume them to be of the same nature, and that whatever has been proved respecting fire-balls will apply equally to the larger shooting-stars. Whether the meteoric appearances to which the latter term is applied may not include objects of totally different natures, is a question admitting a doubt. It is possible that among the shooting-stars there may be objects which are merely electric sparks, or which have their origin in spontaneously-inflammable gases, known or unknown, existing in the atmosphere ; but the greater part of them must be considered as identical with fire-balls. 9. The lunar hypothesis advanced by Laplace, Berzelius, and others, to explain meteoric stones, appears to be attended with serious difficulties, if, indeed, it be not altogether incompatible with the phenomena of shooting-stars. In order to enter our atmosphere with a velocity of 20 miles in a second, it may be shown that, if they come from the moon, they must have been projected from the lunar surface with a velocity of about 120,000 feet in a second, which may be regarded as almost impossible. It thus appears that those shooting-stars and fire-balls which have the planetary velocity of from 20 to 40 miles in a second, cannot, with any probability, be regarded as having their origin in the moon. Whether any individual bodies, moving with a smaller velocity, may have a lunar origin, is a question which cannot be decisively answered. " To me," says Dr. Olbers, " it does not appear at all probable ; and I regard the moon, in its present circumstances, as an extremely peaceable neighbour, which, from its want of water and atmosphere, is no longer capable of any strong explosions." 10. The hypothesis first suggested by Chladni is that which appears to have met with most favour, having been adopted by the most eminent astronomers of the present day to explain these phenomena. It consists in supposing that, independently of the great planets, there exist in the planetary regions myriads of small bodies which circulate about the sun, generally in zones, and that some of these zones intersect the ecliptic, and are, consequently, encountered by the earth in its annual revolution. The principal difficulties attending this theory are the following : 11. First, that bodies moving in groups in the circumstances supposed, must necessarily move in the same direction, and con- sequently they must become visible from one point and move 350 SHOOTING STARS AND FIRE BALLS. toward the opposite. Now, although the observations seem to show that the predominating direction is from north-east to south- west, yet shooting-stars are observed on the same nights to emanate from all points of the heavens, and to move in all possible directions. Secondly, their average velocity (especially as determined by Wartmann) greatly exceeds that which any body circulating about the sun can have at the distance of the earth. Thirdly, from their appearance, and the luminous train which they generally leave behind them, and which often remains visible for several seconds, sometimes for whole minutes, and also from their being situated within the earth's shadow, and at heights far exceeding those at which the atmosphere can be supposed capable of supporting combustion, it is manifest that their light is not reflected from the sun ; they must therefore be self-luminous, which is contrary to every analogy of the solar system. Fourthly, if masses of solid matter approached so near the earth as many of the shooting-stars do, some of them would inevitably be attracted to it ; but of the thousands of shooting- stars which have been observed, there is no authenticated instance of any one having actually reached the earth. Fifthly, instead of the meteors being attracted to the earth, some of them are observed actually to rise upward, and to describe orbits which are convex toward the earth, a circumstance of which, on the present hypothesis, it seems difficult to give any rational explanation. From the difficulties attending every hypothesis which has hitherto been proposed, it may be inferred how very little real knowledge has yet been obtained respecting the nature of the shooting-stars. It is certain that they appear at great altitudes above the earth, and that they move with prodigious velocity, but everything else respecting them is involved in profound mystery. From the whole of the facts, M. Wart- mann thinks that the most rational conclusion we can adopt is, that the meteors probably owe their origin to the dis- engagement of electricity, or of some analogous matter, which takes place in the celestial regions on every occasion in which the conditions necessary for the production of the phenomena are renewed. The presumption in favour of the cosmical origin of the shooting-stars is chiefly founded on their periodical recurrence at certain epochs of the year, and the extraordinary displays of the phenomena in various years on the nights of the 12th or 13th of November. 151 METEORIC STOKES AND SHOOTING STARS. We shall here state the principal circumstances accompanying those of 1799, which put the notion of a lunar origin entirely out of the question. 12. On the morning of the 12th of November, 1799, before sun- rise, Humboldt and Bonpland, then on the coast of Mexico, were witnesses to a remarkable exhibition of shooting-stars and fire- balls. They filled the part of the heavens extending from due east to about 30 toward the north and south. They rose from the horizon between the east and north-east points, described arcs of unequal magnitude, and fell toward the south ; some of them rose to the height of 40, all above 25 or 30. Many of them appeared to explode, but the larger number disappeared without emitting sparks ; some had a nucleus apparently equal to Jupiter. This most remarkable spectacle was seen at the same time in Cumana, on the borders of Brazil, in French Guiana, in the channel of Bahama, on the continent of North America, in Labrador, arid in Greenland; and even at Carlsruhe, Halle, and other places in Germany, many shooting-stars were seen on the same day. At Nain and HofFenthal in Labrador, and at Neuernhut and Lichtenau in Greenland, the meteors seem to have appeared the nearest to the earth. At Nain they fell toward all points of the horizon, and some of them had a diameter which the spectators estimated at half an ell. See Humboldt's " Recueil des Voyages," &c., vol. ii. 13. A not less stupendous exhibition took place in North America on the night of the 12th of November, 1833. In 1834 similar phenomena occurred on the night of the 13th of November ; but on this occasion the meteors were of a smaller size. In 1835, 1836, and 1838, shooting-stars were observed on the night of November 13th, in different parts of the world, but though diligently looked for on the same nights in 1839 and 1840, they do not appear to have been more numerous than on other nights about the same season of the year. 14. The second great meteoric epoch is the 10th of August, first pointed out by M. Quetelet, and although no displays similar to those of the November period have been witnessed on this night, there are more instances of the recurrence of the phenomena. In 1838, 1839, 1840, shooting-stars were observed in great numbers both on the 9th and 10th ; but they appear in general to be unusually abundant during the first two weeks of August. The other periods which have been remarked, are the, 18th of October, the 23rd or 24th of April, the 6th and 7th of December, the nights from the 15th to the 20th of June, and the 2nd of January. 15. Halley first suggested the idea that the shooting-stars 1*2 HUMBOLDT AND BOXPLAND. may be observed as signals for determining differences of longi- tude by simultaneous observations, and Maskelyne in 1783 published a paper on the subject, in which he calls the attention of astronomers to the phenomena, and distinctly points out this application. The idea was revived by Benzenberg in 1802, but so long as they were regarded merely as casual phenomena, it could scarcely be hoped that they would be of much use in this respect to practical astronomy. As soon, however, as their periodicity became probable, the phenomena acquired a new in- terest, and some recent attempts to determine longitudes in this manner have proved that the method is not to be disregarded. The probability of the conjecture that the causes of the meteoric phenomena observed in the months of August and November is to be found in the fact that the particular regions of the solar system through which the earth passes at these seasons, are the seats of an unusual quantity of the matter composing these meteors, must in a great degree depend on the extent to which it can be proved by observation that such meteors do really prevail at each of those periods of the year. 16. With a view of testing this, we have collected together, from various sources, the dates of the most remarkable atmospheric appearances of this class from the eighth century to the present time. In the table in the following page, the day of the month when it has been recorded, is placed in the column under the month, and in the line with the year of the occurrence. Where an asterisk occurs under the month, the particular night has not been recorded, but the appearance has merely been mentioned as having occurred. 17. There are here recorded fifty-two nights on which these ap- pearances prevail to such a degree as to attract particular notice. Of these, twenty-six occurred between the 8th and 15th of August, and thirteen the 6th and 19th of November. Thus three- fourths of the nights recorded correspond to the epochs to which we have referred. Some disappointment was produced in 1837, by the circum- stance of an unusually small number being seen on the night between the 12th and 13th, arising from an erroneous impression that that was the night on which their periodical return should be expected. It will be seen, however, from the preceding table, that these appearances have not at all been confined to the night of the 12th ; but independently of this, the night of the 12th at Paris was so bright, that stars of the second magnitude were not visible, and consequently meteors even supposing them to have existed of similar or of inferior brightness could not have been observed. It should also be considered, that their non-appearance 153 METEOEIC STONES AND SHOOTING STARS. at any particular place is no proof of their non-existence in our atmosphere. They may be produced during the day, or they may be produced in a part of the atmosphere not visible from the place in question. Thus, in 1833, when they were a general object of terror to the people of America, they attracted but little attention in Europe. On the other hand, they sometimes appear contemporaneously in the atmosphere on opposite sides Years. Jan. Feb. March. April. May. June. July. AUK. Sept. Oct. Nor. Dec. 763 902 * * 1029 ^ 1092 1202 25 19 1741 25 1777 1779 17 9 1781 1784 1785 i7ys ' 27 27 8 9 7 1799 9 11 1S03 1805 1806 1811 1S12 1813 ' is 2 ' io 10 11 23 ? 8 1815 10 1818 14 19 1819 1819 6 13 1820 1822 9 o 10 12 12 1823 15 10 1824 1826 14 14 6 1827 10 14 1828 10 1829 14 1830 12 1831 13 1832 13 1833 1834 .. 10 10 13 13 1835 1836 10 8 13 13 1837 ' 10 10 of the globe. In 1837, they were observed from the French ship fionite, on the other side of the globe, while on the same day iii Europe a vast number appeared. 18. On the night of the 12th of November, 1836, Sir John Herschel observed these phenomena at the Cape of Good Hope. Their number was not very considerable, but their motion had a I'M EPOCHS OF SHOOTING STARS. marked regularity ; they appeared to diverge from a centre or focus, which preserved a fixed position with respect to the horizon, but had no such fixed relation to the objects on the firmament. This point, or centre, to which their common directions converged, was a point of about thirty degrees above the horizon, and sixty degrees west of north. 19. On the night of the 9th of August, 1837, M. Wartmann ob- served these phenomena at Geneva ; between nine o'clock, P.M., and midnight, eighty-two were seen in different parts of the heavens. They were most frequent about ten o'clock, and then appeared to emanate from a centre or focus situated between the star , in the constellation of Bootes, and the star A, in the con- stellation of the Dragon. At a quarter past ten, twenty- seven were seen, and were remarkable for their bright bluish light. Other observers in the same neighbourhood, and on the same night, counted one hundred and forty-nine in one part of the heavens, between a quarter before nine and half-past eleven o'clock. Of these hundred and forty-nine meteors, three had the appearance of round disks, or globes, of a ruddy red colour, measuring from four to five minutes in diameter, being about one-sixth part of the moon's diameter. Twenty-six were more brilliant than the planet Venus, and of resplendent whiteness ; the remainder had the appearance of stars from the first to the third magnitude, their colours varying between blue, yellow, and orange. 20. On the night of the llth of November, 1832, M. Tharand, a retired officer at Limoges, stated that workmen who were employed in laying the foundation of the bridge over the river Vienne, observed the firmament brilliant with meteors, which at first only amused them, but after some hours the number and splendour of these luminous appearances were so greatly augmented, that the people were seized with panics, and so great was their terror, that they abandoned their labour, and flew to their families, exclaiming that the end of the world had arrived. On the next day these people were interrogated on the subject, and their accounts varied according to the different impressions which had been produced on their imaginations. Some declared that they saw streams of blue fire ; others that they beheld bars of red iron crossing each other in all directions ; others, that they beheld an immense quantity of flying rockets. All agreed that the phenomena were diffused over every part of the firmament ; that they commenced at eleven o'clock, and continued till four the next morning. 21. There appears some reason for supposing that November and August are not the only times of the annual recurrence of these 155 METEOKIC STONES AND SHOOTING STARS. meteors. Arago lias suggested the probability of their periodical recurrence between the 22ud and 2oth April. Humboldt thinks that other annual periods may be assigned to the 6-1 2th De- cember, and Capocci has assigned the 17th July, and the 27-29th November as the dates also of their probable periodic occurrence. On the night of the 6th December, Brandt observed and counted 2000 shooting-stars; and on the llth December, 1836, according to Humboldt, an immense fall of aerolites took place in Brazil, near the village of Macao, on the banks of the river Assn. In the interval between 1809 and 1839, Capocci shows that twelve falls of aerolites took place between the 27th and 29th November, besides others oil the 13th November, 10th August, and 17th July. On the whole, the following appear to be the dates at which the recurrence of these meteors may be looked for : 22-25th April. 17th July. 10th August. 12-14th November. 27-29th November. 6-1 2th December. From all this it must be inferred that those parts of its annual orbit through which the earth passes at these dates severally, are intersected by the orbits of those groups of bodies, which, when passing near the earth, present the appearance of shooting- stars, or aerolites. 22. From all that has been stated it may be considered then as demonstrated w r ith the highest degree of probability, if not with moral certainty, that the phenomena called shooting-stars, fire-balls, and meteoric stones are identical ; that these latter bodies belong not to the earth, but are masses of matter moving like the planets in the celestial spaces, subject to the gravi- tating attraction of the sun ; that the earth encounters them occasionally, either striking directly upon them, or approaching so close to them that they are drawn by the terrestrial attrac- tion, first within the atmosphere, and afterwards to the surface ; that the shooting-stars, which rush athwart the heavens without falling on the earth, are the same class of bodies which do not either directly strike the earth or come so close to it as to be drawn to its surface by its attraction. Since it is supposed that these bodies become visible only after they enter the atmosphere, being there rendered luminous by the heat which they develop by the sudden and violent compression of that fluid, it is probable that they may be passing around us in countless numbers, outside the atmo- 166 ZODIACAL LIGHT. sphere, without the possibility of being seen or observed. It may be objected that they would be illuminated by the sun's light, as the moon and planets are, and must thus be rendered visible. Their extreme minuteness, however, affords a satis- factory explanation why they are not visible by the light which they reflect. Compared with the planets, as Sir J. Herschel observes, which are visible in our most powerful telescopes, rocks and stony masses of great magnitude and weight would be but as the impalpable dust which a sunbeam renders visible as a sheet of light, when streaming through a narrow chink into a dark chamber. It has nevertheless been affirmed that occasions have been recorded on which the sun's light, at noon-day and in an unclouded sky, has become sensibly obscured during certain intervals of time, which has been explained by the supposition that at such times a flight of meteoric stones were passing between the sun and the earth, so as partially to intercept the sun's light. A stony mass which would weigh an hundred tons, however strongly illuminated by the sun's light, would not be visible at the distance of eight hundred or a thousand miles. 23. Sir John Herschel supposes it probable that the sun is surrounded by a mass of nebulous matter of greater or less extent, such as is seen around many of the stars, and that the phenomenon called the zodiacal light, as well as meteoric stones and shooting-stars, are mere manifestations of this nebulous matter. The zodiacal light is explained by the supposition of an oval spheroid of nebulous matter surrounding the sun, the larger diameter of which coincides with the solar equator. In fig. 2, s s represents the sun's equator, and A B A' B' the oval mass of surrounding nebulous matter shown by its section made by a plane through the axis of the sun, the section by a plane through the sun's equator being a circle whose diameter is A A'. 157 METEORIC STONES AND SHOOTING STARS. The semi-diameter c A of this lenticular mass is nearly equal to that of the earth's orbit, so that at certain times the earth grazes its edges at A and A', and probably may pass through a portion of the nebulous matter. 24. If this matter consist to any extent of solid masses of small dimensions, they may pass through the earth's atmo- sphere, on these occasions producing the phenomena of shooting- stars, or they may strike the surface or be drawn down upon it by terrestrial gravitation, and produce the phenomena of meteoric stones. The appearance of the zodiacal light is easily explained. Let H o represent the line in which the plane of the horizon intersects the lenticular nebula after sunset. In that case, o A' H will be below, and o A H above the horizon. The matter composing o A H being illuminated by the sun will, so far as it may have reflective power, be visible. In fact it is seen in certain positions of the earth in relation to the sun. It presents the appearance of a faint and ill-defined comet, and is usually seen soo.n after sunset about the months of March, April, and May, and before sunrise about the months of September, October, and November. It appears as a luminous cone extending from the horizon obliquely upwards as has been already stated in the direction of the solar equator, and therefore nearly in that of the ecliptic, or the zodiac, and hence has been called " zodiacal light." The semi-diameter A c subtends an angle at the earth, which varies with the position of the earth from 40 to 90. In some cases, therefore, the vertex A is near the zenith, when the sun is below the horizon. The breadth B B', of the base of the sun subtends an angle which varies from 8 to 30. The zodiacal light is very faint and ill-defined when seen in the higher latitudes, but is much brighter and clearer within the tropics. The matter composing this nebulous envelope of the sun may, according to Sir J. Herschel, be conjectured to be no other than the denser part of that medium, which, we have some reason to believe, resists the* motion of the comets, loaded perhaps with the actual materials of the tails of millions of those bodies, of which they have been stripped in their suc- cessive visits to the sun. An atmosphere of the sun the zodiacal light cannot be, in any proper sense of that term, since the existence of a gaseous envelope propagating pressure from part to part, subject to mutual friction in its strata, and therefore rotating in the same or nearly the same time with the central body, and of such dimensions, and ellipticity, is utterly incom- 158 MAY BECOME SATELLITES TO THE EARTH. patible with dynamical laws. If its particles have inertia they must necessarily stand, with respect to the sun, in the relation of separate and independent minute planets, each having its own orbit, place of motion, and periodic time. The total mass being almost nothing compared with that of the sun, mutual perturbations are impossible, though collisions between such as may cross each other's paths, may operate in the course of indefinite ages to effect a subsidence of at least some fraction of it into the body of the sun or those of the planets.* 25. There are certain supposable circumstances under which the earth might pass near to one of these masses, the conse- quence of which would be that it would become a satellite of the earth, and would accompany it as the moon does in its course round the sun, and would, if it were large enough, be visible by reflected light like the moon. But since, so far as is yet known, these bodies are far too small to be seen thus at any distance, at which they could possibly revolve without being speedily arrested by the resistance of the atmosphere, and brought down to the surface by terrestrial gravitation, it follows that the earth may actually be attended by hundreds of such invisible moons. Sir J. Herschel is even of opinion that these not only exist, but that some of them may be so large, and of such texture and solidity, as to shine by reflected light, and become visible (such at least as are very near to the earth) for a brief moment, suffering extinction by plunging into the earth's shadow, in other words undergoing total eclipse.t Sir John Lubbock is of opinion that such is the case, and has sup- plied rules and mathematical formulae for calculating their distances from observations of this kind.tjl 26. M. Petit, Director of the Observatory of Toulouse, has made observations and calculations of this kind, which induces him to conclude that there is at least one meteoric stone of con- siderable magnitude, which is attached as a satellite to the earth. Its orbit is at about 5,000 miles from the surface, and therefore 9,000 miles from the centre, or about twenty-six times nearer than the moon. It makes a complete revolution in three hours and twenty minutes, and therefore revolves round the earth about seven times per day. 27. In enumerating the hypotheses which have been proposed to explain the phenomena of aerolites, we have omitted to notice one, which, if for no other reason, may be regarded as entitled at least to be mentioned on account of its antiquity. As the Herschel's Astron., p. 616. f Ibid., p. 521. + Phil. Mag., 1848, p. 80. Comptes rendus, Acad. Sc., Oct. 12th, 1846, and Aug. 9th, 1847. 159 METEORIC STONES AND SHOOTING STARS. supposed lunar origin of these bodies gave them the name of " MOON-STONES," the hypothesis we refer to conferred upon them that of " SUN-STONES." Diogenes Laertius records an opinion which prevailed in Greece, that the meteoric mass of ^Egos potamos fell from the sun ! Pliny, deriding the supposition, charges Anaxagoras with having predicted the fall of aerolites from the sun. Humboldt suggests the probability that the fall of aerolites during bright sunshine, and when the moon was not visible, may have led to the idea and name of sun-stones. 160 RAILWAY ACCIDENTS. CHAPTEE I. 1. All travelling attended with danger. 2. Awful disasters incidental to railway travelling. 3. Is railway travelling, however, really more dangerous? 4. Not practically so considered. 5. The real amount of danger may be calculated. 6. Utility of such a calculation. 7. Imperfections of official reports. 8. Necessary to compare acci- dents with total amount of travelling. 9. Example illustrating this. 10. Necessary data given in official reports. 11. Reports of 1847-8 and 1850-1. 12. Total mileage of passengers in these intervals. 13. Computation of the risk to life and limb in a journey of given length. 14. Tabular statement. 15. Analysis of its results. 16. Classifi- cation of accidents in relation to their causes. 17. The greatest disasters arise from imprudence. 18. Accidents to railway servants. 19. No progress observable in railway safety. 20. Accidents on foreign railways Risk on Belgian lines. 21. Accidents on French railways. 22. Contrasted with accidents by stage coaches in and near Paris. 23. Frequent departures, great expedition, and numerous stoppages create danger of collision. 24. Liability to collision with express trains. 25. Accidents by escaping rails. 26. Neglect of points and switches. 27. Analytical table of proportion of causes of accident in 100 cases. 28. Number of brakes. 29. Greater number of brakes necessary with fast trains. 30. Danger of bringing trains to rest too suddenly. 31. Danger of reversing action of engine. 32. Fog signals. 33. Consequences of collision aggravated by manner of connecting vehicles. 34. Derailment of carriages. 1. WHATEVER maybe the agency by which personal locomotion is produced, it has always been attended wWi more or less danger to life and limb. If one age or country be compared LARDNER'S MUSEUM OF SCIENCE. M 161 No. 9 KAILWAY ACCIDENTS. with another, the result will only amount to a difference in the degree of the danger, or in the gravity of the catastrophe pro- duced by an accident. So universal and so ancient is this danger, that in the form of prayer ordained by the Church, travellers by laud and water are included among the classes more especially and emphatically entitled to the supplications of the people. 2. The progress of civilisation, the development of commerce, the increase of population, and the discoveries of science, have stimulated and increased personal locomotion on an immense scale. The risk attendant upon it, and the character of the danger incident to it, have varied with every change in the physical or mechanical expedients by which this locomotion has been effected. The spectacle exhibited on the occasion of some great railway collisions would have been deemed by our forefathers too extravagant even to be allowed a place in the wildest fictions. Colossal vehicles, weighing several tons, shivered to pieces ; rods of iron, thick and strong enough to sustain a vast building, bent, twisted, and doubled up as though they were rods of wax ; massive bars of metal snapped and broken like glass ; bodies of the killed dispersed here and there, amongst the wrecks of vehicles and machinery, so mangled as to render identification impossible limbs, and even heads, severed from the trunks, and scattered right arid left, so as to render it impossible to re- combine the disjecta membra of the same body the coun- tenances of the dead, where countenances remain at all, having a ghastly expression of the mingled astonishment and horror with which the sufferer was filled in the brief instants which elapsed between the catastrophe and death ; the survivors, maimed and wounded, lying under the ponderous ruins, groaning in agony and supplicating for relief and extrication ! These are incidents with which the vast improvements introduced by science into the art of locomotion have unhappily rendered us familiar, and which assuredly have had no parallel in the days of waggons and stage-coaches, to say nothing of those of pack- horses and saddle-bags. 3. Are we thence to infer that the great mechanical inventions which have signalised this age of ours, are attended with the serious drawback of exposing us to greater risk and more terrible dangers than any which were known in less advanced and enlightened times ? Is the traveller at fifty miles an hour by steam, on railway, in the nineteenth century, really exposed to greater risks, and does he really need the prayers of the Church more urgently than the wayfarer of the beginning of the eighteenth 1 That disasters do occasionally occur, which were 162 THEIR AWFUL EFFECTS. never known in former times, is undeniable ; but that the risk to life ami linib has been augmented, is a conclusion which we should only be justified in assuming after a much more rigorous examination of the question. 4. Meanwhile, it may be observed that, notwithstanding the degree to which imaginations may be excited, and fears aroused by such recitals as we have described, still the public instinct, independent of any rigorous statistical analysis of the point, has resisted all exaggerated estimate of the danger, and it is incontestable that travelling over land was formerly regarded with greater apprehension of danger than at present. A century has not elapsed since no prudent person would start upon a journey, say from Exeter to London, without a solemn farewell of his kindred and the deposition of his last will and testament in trustworthy hands. 5. To prevent exaggerated apprehensions of danger, and reduce the fears of the timid within reasonable limits, it will only be necessary to investigate the actual extent of the danger, by comparing the number of casualties with the number of persons who travel, taking into account the distances over which they are transported. By this means the real risk of life and limb incurred by a railway traveller can be determined with as much arithmetical precision as that with which the average duration of life is computed from the tabular reports of births and deaths ; and we know that the latter has been determined with all the exactitude and certainty necessary to render it the basis of the operations of commercial institutions for life insurance, involving many millions of capital. 6. To do justice at once to the public who are the victims of these casualties, and to the railway administration to whose negligence and mismanagement they are generally ascribed, it- will be only necessary to ascertain the causes which in each case have produced them. So far as they may prove to arise from the imperfections which are incidental even to the irfost efficient and best constructed machinery, they must be submitted to as inevitable. Happily, however, the proportion of casualties which admit only of this explanation, is infinitesimally minute. So far as they shall appear to arise from maladministration, as from overcrowding the lines with traffic, overloading the engines, or what is the same, providing an insufficient stock of locomotive power, or from the negligence or insufficiency of the railway servants, the executive bodies of the railway companies must be held accountable, and the prevailing character of the accidents will indicate the direction in which administrative reform may be required. So far ; in fine, as they mav appear to arise from M2 163 RAILWAY ACCIDENTS. imprudence or want of due care and precaution on the part of the traveller himself, a case of frequent occurrence, the railway managers and the railway machinery must stand acquitted, and the character of the casualty will indicate the nature of the precautions which are necessary on the part of passengers, to guarantee them from its recurrence. 7. To estimate the chances of accident fatal to life or limb, it is not enough to compare the number of passengers killed or injured with the total number booked at the stations. This is an error which is very apparent, yet it has been committed year after year without correction by the government railway com- missioners in their reports. Such an estimate is based upon the implied assumption that all passengers run the same risk, what- ever be the distances they travel. Thus, a passenger booked from London to Aberdeen is assumed to incur no more risk than one who travels from London to Greenwich. It is evident, on the contrary, that the risk incurred, other circumstances being alike, is in the exact proportion of the distance travelled. A passenger who travels an hundred miles is exposed to ten times as much risk of accident as one who travels only ten miles. The premium upon insurance against railway accident should obviously be a mileage. 8. To ascertain the extent of the danger incurred in travelling on any proposed system of railways, it would, therefore, be necessary to compare the number of accidents which take place in any given time, a year, for example, with the total mileage of the passengers in the same interval. This mileage may always be determined with great precision. It is the sum total of the distances travelled by all the passengers booked in that interval. Now, since the fares paid by the passengers of each class bear a fixed average proportion to the distances to which they travel, their total mileage will be found with all the necessary exactitude by dividing the gross receipts arising from each class by the average fare* per mile. 9. To render this method of investigation more clear, let us suppose, that in a given time the quantity of passenger traffic which has taken place on a given system of railways, is repre- sented by an hundred millions of miles, that is to say, that all the distances travelled by all the passengers booked, when summed up, will make an hundred millions of miles. This would then Joe the same as if a million of passengers were trans- ported over a distance of an hundred miles. Now, let us suppose that in the same interval ten passengers were killed, and an hundred wounded by accidents occurring in their transport. It would then follow, that of a million of 164 WHAT IS THE RISK? passengers travelling an hundred miles ten would be killed and an hundred wounded. The risk of life in such a journey would, therefore, be 1 to 100,000, and the risk of personal injury, not causing death, would be 1 to 10,000. That is to say, when a traveller undertakes a railway trip of an hundred miles on that system of railways, the chances against his being killed are 100,000 to 1, and the chances against his being injured, without loss of life, are 10,000 to 1.* 10. The official returns, published annually by the Board of Trade, supply all the data which are necessary to ascertain the actual amount of danger incurred in railway travelling in the United Kingdom. We propose, in the present tract, to apply to the data thus supplied the principles of calculation explained above, so as to ascertain what is, under the existing system of railway management, the actual risk to life and limb incurred by a railway traveller. By applying the same calculation to different intervals, we shall see whether the disasters which have from time to time been reported, have caused such improved management as to diminish the risk in any sensible degree. 11. The following is the classified summary of the accidents reported as having taken place on the railways of the United Kingdom in 1847-8 : Analysis of the Railway Accidents for the Two Years ending December 31, 1848. Killed. Injured. Passengers suffering from causes beyond their own control Passengers suffering from causes which they might have prevented Railway servants suffering from causes beyond their 28 23 30 215 13 57 Railway servants suffering from causes which they might have prevented Trespassers and strangers suffering from crossing or standing on the railway Persons suffering from misconduct of railway servants . 232 96 2 2 85 22 1 413 393 * More exactly the chances would be 999,999 to 1 in the former case, and 99,999 to 1 in the latter. We have preferred the round numbers as being more simple, and sufficiently exact for all practical purposes. It is easy to see how from these data the risks attending other distances would be calculated, since the risk would vary in the exact ratio of the 165 RAILWAY ACCIDENTS. The following is a like summary for 1850-1 : Analysis of Railway Accidwits for the Two Years enditig December 31, 1851. Killed. Injured. Passengers suffering from causes beyond their own control 31 526 Passengers suffering from causes which they might have prevented ........ 37 32 Railway servants suffering from causes beyond their own control ........ 129 69 Railway servants suffering from causes which they might have prevented ...... 116 42 Trespassers or strangers suffering from crossing or standing on the railway 113 24 Persons suffering from misconduct of railway servants . Suicides 8 434 693 12. To deduce from these reports any certain conclusions, either as to the danger incurred by the railway traveller or the efficiency of the railway management, it will be necessary to ascertain in each case the total mileage of the passengers trans- ported, and to compare with this mileage the accidents. By means of the returns of the passenger traffic, compared with the average fares in proportion to distance, it appears that the total mileage of the passengers of all classes in each of the intervals to which the above returns refer, was as follows : Mileage of Passengers. In two years ending 31st Dec., 1848 . . 1830,184617 In two years ending 31st Dec., 1851 . . 2282,752756 The meaning of these numbers is, that the total movement of passengers on the railways was the same as if 1830,184617 had been carried one mile in 1847-8, and 2282,752756 had been carried one mile in 1850-1. By comparing the number of killed and wounded with these numbers, it will be easy to determine the number of persons of each class which were killed and wounded in the transport of a given number of passengers over a given length of railway. 13. Let it be required, for example, to determine the numbers distances travelled. Thus, if the risk in travelling 100 miles be 100,000 to 1, the risk in travelling 200 miles will be 100,000 to 2, or 50,000 to 1, and the risk in travelling 50 miles will be 100,000 to i, or 200,000 to 1, and so on. 166 ANALYSIS OP CASUALTIES. of each class of persons who were killed and injured in the transport of a million of passengers over an hundred miles of railway, in each of the intervals of two years to which the preceding returns refer. This is effected by a simple proportion, and is, in fact, nothing more than a question in the rule of three. As the total mileage divided by an hundred is to the number of accidents reported, so is a million to the number of accidents produced in the transport of a million of passengers an hundred miles. The following are the results of such a calculation : 14. Table showing the mean numbers and classes of persons kitted and injured in the transport of a million of passengers over an hundred miles on the Railways of the United Kingdom. 1S47-8. 1850-1. Killed. , Injured. Killed. Injured. Passengers from causes beyond their control . 1-53 ... 11-75 ... 23-04 ... , Passengers from causes within their control . 1-26 0-71 1-62 ... 1-40 Total . . 2-79 ... 12-46 ... 2-98 24-14 Railway servants from causes beyond their control . 1-64 3-11 ... 5-65 3-02 ... : Railway servants from . causes within their control . . .12-65 4-64 5-08 ... 1-84 ... Total . ! ... 14-32 7-75 ... 10-73 ... 4-86 Trespassers & strange: - 5-25 1-20 1-20 4-95 4-95 1-04 1-05 Grand total . . 23-36 ... 21-41 ... 18-66 ... 30-35 15. The numerical results consigned to this small table, when clearly comprehended, are full of interest and importance ; of interest and importance not merely to the travelling public who are exposed to these dangers, but to the railway directors, as indicating the real proportion which such disasters bear to the total amount of personal locomotion, and to the government authorities whose duty it is to see that the greatest practicable precautions are adopted for the public safety. For the benefit of those who are less accustomed to deal with such arithmetical results, we shall here examine some of the consequences deducible from this table. It appears that in 1850-1, 2'98, or very nearly three passengers in every million who travelled one hundred miles were killed. 167 EAILWAY ACCIDENTS. The chances therefore of safety for life in the case of any individual traveller were 1,000,000 to 3, or 333,333 to 1. In like manner, 24*44 in every million were wounded, maimed, or more or less injured. The chances against personal injury in the case of each individual were therefore 1,000,000 to 24'44, or very nearly 40,000 to 1. Notwithstanding the gravity of some of the accidents which are recorded, it must therefore be acknowledged that there is no very great amount of danger in railway travelling. 16. The classification of accidents to passengers into such as arise from causes beyond their control, and which proceed from their own imprudence and want of due caution, merits especial attention. It appears that in 1850-1, more than half the acci- dents fatal to life belonged to this class. But the most remark- able feature of these accidents is the immense proportion of the entire number which are fatal. Of the accidents which arise from causes beyond the control of the passenger, only 1 in 18 results in loss of life, while more than the half of those arising from imprudence are fatal. 17. These remarkable proportions are equally manifested in 1847-8, and 1850-1, and as we have found them also to prevail in other periods, they may be regarded as a fixed law of personal locomotion by railway. The railway traveller will therefore do well to remember that small as is the amount of risk he incurs, one-half of it depends on his own incaution, and may be altogether eliminated by his own prudence and vigilance, and further that the part of the risk which arises from his imprudence is for the most part the risk of his life, and not merely the risk of personal injury. 18. It appears further that the transport of a million of passengers 100 miles, costs the lives of eleven railway servants and five strangers who chance to be on the road, and produces more or less bodily injury to five of the former and one of the latter class. In the gravity of the accidents from which these latter classes suffer, nothing is more remarkable than the large proportion of them which are fatal to life, and which arise from imprudence on the part of the sufferer. Thus, of fifteen railway servants who incurred accidents, eleven were killed, one-half of whom suffered through their own want of due caution. Of six strangers and trespassers who suffered from accidents, five were killed. 19. In fine, it appears from the table that in 1847-8, the transport of a million of passengers 100 miles, cost the lives of 168 CHANCES AGAINST ACCIDENT. 23 and the injury of 22 persons of all classes, and that the same amount of passenger traffic in 1850-1, cost the lives of 19 and the injury of 30 persons. The total number of sufferers being 45 in the former and 49 in the latter period. So far therefore as the aggregate of the sufferers from accidents can be taken as exponents of the efficiency of railway management, no very sensible improvement seems to have taken place in the five years over which these reports extend. 20. On the foreign railways it might be expected that the prevalence of accidents would be less, owing to the less crowded state of the lines. On the Belgian railways, during the three years ending 1st December, 1846, there were but three passengers killed by causes beyond their control. The total mileage of the passengers was 239,629541, from which it follows that in the transport of a million of passengers an hundred miles, the number of passengers killed by causes beyond their control, was 1'25, being very little less than on the English railways. 21. On the French railways, accidents have been still more rare. One fatal accident occurred many years ago on the Paris and Versailles Railway, on which occasion a train took fire, and appalling consequences followed. Another serious accident occurred on the Fampoux embankment of the Northern Railway in 1846. These however stand almost alone. In the two years ending 31st December, 1848, there was not a single fatal accident to a passenger reported on any French railway. 22. It may not be uninteresting to put in juxtaposition with this the returns of accidents produced by ordinary horse- coaches travelling in Paris and its environs : Year. Killed. Wounded. 1S34 4 134 1835 12 214 1836 5 220 1S37 11 361 1S39 19 366 1839 9 384 1840 . 14 394 Total . . . 74 2073 23. However insignificant may be the proportion of the number of persons injured to the total amount of passenger traffic, it may not be without interest or utility to inquire into the causes which produced these accidents. The causes which are not dependent on the imprudence of the sufferers are, generally, either collision of the passenger train 169 - RAILWAY ACCIDENTS. with some other carriages or waggons, or the escape of the train, or some part of it, from the rails. The English railways are in general constructed with double lines, the train observing the common rule of the road, and keeping always on the left-hand line. The consequence of this is, that, in regular work, all trains upon the same line move in the same direction. The collision of one train with another, therefore, can only take place by a faster train overtaking a slower, or a train running into one which is at rest. It is evident, therefore, that, if all trains moved with the same speed, and all stopped at the same stations, no collisions could ever happen, except when a train should be retarded or stopped by accident, or in the case of a vehicle being improperly left standing on the line. The probabilities of collision will therefore depend on the differences between the speed with which the several trains travel, and the differences between the number of stations at which they stop. But, on railways as worked at present, it is impracticable to maintain uniformity of speed. Passenger and goods traffic being necessarily worked on the same lines of rails, and the latter being carried at less speed than the former, a source of danger is produced. If the present enormous amount of trans- port had been foreseen when railways were in an early stage of their progress, it might have been a question for consideration whether it would not have been advantageous to construct the trunk railways with three lines of rails, reserving one line exclusively for the goods traffic. This would have been infinitely more politic than augmenting the capacity of the railway by increasing the width of the rails, and, consequently, the magni- tude and weight of the engines and vehicles of transport. But the railways being constructed, it is now too late, and nothing remains to be done but to adopt the most efficient precautions against those collisions, the probability of which is augmented with the frequency of the trains, and the differences of their average speed. 24. The accommodation of the public requires frequent departures, great expedition, and means of arriving at numerous intermediate points of lines. These demands cannot be satisfied without calling into existence all the conditions which are pro- ductive of the danger of collision. To satisfy the urgent call for great expedition, express trains are despatched at extraordinary speed, stopping only at chief stations. To satisfy the want of intercommunication with the intermediate stations, trains are despatched which stop at all 170 CAUSES OF COLLISION. the stations ; and as the stations, on the average, are not four miles asunder, these trains must be almost continually in a state either of retarded or accelerated motion. They scarcely get up their speed after starting from one station, before they are obliged to slacken their pace, in order to stop at the next. The average speed of such trains is therefore comparatively small. Between these and the express trains, which present the extremes of speed, there are several which move at intermediate average rates, stopping fess frequently than the one, and more so than the other, and, when at full speed, proceeding with a less velocity than the express trains. When all these circumstances are taken into account, and when it is also considered that, on some of the great trunk lines, such as the North- Western, as many as fifty trains pass over the same rails every twenty -four hours, much more than the half of which are worked during the day, and therefore succeed each other at very short intervals, the wonder is, not that collisions occasionally occur, but that a movement so crowded and com- plicated can be conducted at all, without most imminent danger. The most frequent source of accidents from collision, arises from single waggons or trucks being left standing upon the rails. When express trains have to be stopped, the steam must be cut off, and the brakes applied at a considerable distance from the place where they come to rest. Hence arises the greater liability of accidents by collision with these trains. If an obstacle is observed upon the railway by the engine-driver, it must be noticed at a distance so great as to render it possible to stop the train, otherwise collision must take place. One railway accident is often the cause of another, and colli- sions frequently arise in this way. When an accident occurs to a train, by which it, or part of it, is detained upon the line for any length of time at a place where, in the regular course of the railway traffic, it ought not to be found, trains following on the same line of rails, not expecting to encounter such an obstacle, are liable to a collision with it. In all such cases, the guards or conductors run back upon the line, and if the accident take place at night, make signals with their lamps to warn the approaching train of the obstacle. In certain classes of accident, both lines are obstructed, and such precautions must be taken in both directions as, for example, when a train or part of it running off the rails, the engine, carriages, or waggons are thrown some on one line of rails and some on the other. In this case, one messenger is sent along the up and another along the down line to warn approaching trains to stop. 171 RAILWAY ACCIDENTS. 25. Next in frequency to accidents from collision, are those which arise from the engine or the vehicles escaping from the rails. The causes which produce this class of accidents are very various. The most frequent are impediments left on the rails, such as blocks of wood, bars of iron, spare sleepers or rails. The engine encountering obstacles of this kind is generally thrown off, dragging with it one or more of the carriages. Cattle from adjacent fields, through deficient fences, have sometimes got upon the road, and the engine encountering them has run over them, and been thrown off. A wheel or axle of the engine, tender, or any of the carriages breaking, is sometimes the cause of escape from the rails. A defect in the rails themselves is not unfrequently the cause of this class of accidents. This is especially liable to occur at a joint chair, that is to say, a chair where the ends of two suc- cessive rails are united. It frequently happens that one of these rails is considerably above or below the other, or that the rails are not sufficiently fastened in the chair. The impact of the wheel of the engine on such a defective joint may either imme- diately break the rail, or so weaken it that one of the succeeding carriage-wheels will break it, and the carriages thus escape from the rails. 26. Another not unfrequent cause of accidents is the neglect of the points and switches, a name given to a part of the mechanism by which trains are enabled to pass from one line of rails to another, or from either line into the sidings. When such passage is intended, a certain change is made in the position of the points and switches by a person employed for this purpose on the line, and after the train passes from the line the switches are restored to their usual position. If any neglect take place in this operation, considerable danger will ensue to the trains which next pass. 27. In order to ascertain the proportion in which these causes of accident respectively operate, we have taken indiscriminately, from the returns of accidents, 100 cases, of which the following is the analysis : Accidents from collision 56 broken wheel or axle . . . . 18 defective rail . . . . . 14 by switches ..... 5 impediments lying on road off rails by cattle on line ... 3 bursting boiler .... 1 100 172 PREVENTION OF COLLISIONS. Hence it appears that 56 per cent, of these accidents arise from collision. Next to these comes the escape from the rails by the breaking of a wheel or axle, or by defective rails, which together make up 32 per cent., the remaining causes operating in small proportions. Since more than half the total number of fatal accidents which occur upon railways arise from collision, it is important that the attention of railway companies be more specially directed to precautions against this source of danger. Before a collision takes place, the engine-driver and others in management of the following train have, or ought to have, the means of observing the object in advance of them, with which the collision is about to take place. If it be possible to bring the train to rest before it can pass over the length of road between the point where the obstacle has been observed, and the point where such obstacle would be overtaken, the collision will be prevented. This possibility will depend upon the proportion which the number of brakes and brakesmen upon the train bears to its weight and speed. It is clear, therefore, that in all cases the number of brakes provided should have reference to the magnitude and speed of the train. It is found by experience that the distance within which a train of given weight can be brought to rest by a given number of brakes, will be in proportion to the square of its speed, that is to say, with a double speed it will require four times the number of brakes ; with a treble speed, nine times the number of brakes ; and so on. In the case of an accident which occurred near Wolverton on the 5th of June, 1847, it was found impossible to bring a train of 19 carriages to rest within a distance of 540 yards, the speed of the train being about 25 miles an hour. In this case a collision took place by which seven persons were killed : on an inquiry it was found that this train was provided with three brakes, one upon the tender and two upon the carriages. 28. Inquiries suggested by this and other similar accidents, induced the Board of Trade to propose a rule to be observed by railway companies, that a brake should be attached to every fourth carriage. A similar rule was imposed by the French government, in February, 1848, on the trains working on the railways of that country. 29. Since, however, the brake power necessary to stop a train is increased in so large a ratio with the speed, a atill greater number of brakes would be necessary with a fast train, such as the express trains, each carriage of which ought to be provided 173 KAILWAY ACCIDENTS. with an independent brake and brakesman. This would certainly cause a considerable increase in the working expenses of the faster class of trains, but the public safety is a matter of too great importance to be postponed to considerations of this kind. 30. In attempting to avoid one source of danger another is often produced. When an obstacle is seen on the rails before a train moving with great speed, all means must of course be used to bring the train suddenly to rest. But if this be not done with great caution and skill, danger may be produced even more serious than that from which it is attempted to escape. The means of stopping a train are, the brake on the tender, the brakes on the vehicles composing it, and, in fine, reversing the action of the engine. This process consists in so changing the motion of the slides, that the steam shall obstruct instead of accelerating the pistons. In this way the whole force of the steam is suddenly made to resist the progressive motion of the train. 31. This is a dangerous process. The progress of the engine is arrested by an agent which does not act on the vehicles which follow it. The latter are consequently urged against the engine and against each other with all the force of which the engine is deprived by the back action of the steam. The effect is nearly the same as if an engine acting behind the train suddenly pushed the train against the engine in front. The effect of this is an obvious tendency to drive the intermediate carriages off the rails by doubling up the train. Before reversing the engine, or even applying the brake to the tender, it is therefore always advisable to warn the brakesmen to apply the brakes to the vehicles composing the train. This being done, and the brake being then applied to the tender, there is less danger in reversing the steam on the engine. But it unfortunately happens that in the emergencies in which these extreme measures are demanded, there is rarely time to observe these precautions. The prudence of providing a signal on the tender which shall be within view of the brakesmen, and seats for the latter from which they can always see such signal, is so obvious that it need not here be enlarged on. 32. We must not dismiss this subject without noticing the ingenious application of detonating substances, now called fog signals. These are detonating balls, which on being crushed explode with the report of a pistol. When a train is stopped on the line by an accident, or in general when an obstacle is found upon the railway from any unexpected cause, and which cannot be 174 ECCENTBIC BUFFERS. immediately removed, if there be a fog at the time, or any other cause which may prevent the driver of a following train from seeing the obstacle, the guard or policeman runs back along the line and places these balls on the rails at certain distances, so that when a train approaches it causes them successively to explode in rolling over them, and the driver thus receives ^warning to stop. 33. The evil consequences resulting from collision are fre- quently aggravated by the manner in which the carriages or waggons composing the trains are connected with or adapted to each other. The mode of connecting the successive carriages ibrming a train is as follows. From the end of the frame supporting each carriage project two strong iron rods, which rest against spiral springs, and which are terminated by circular cushions, about a foot in diameter, called buffers. "When two successive coaches are brought into contact, these buffers ought to meet each other so that their centres should coincide. This requires that the buffers of all the carriages should have the same gauge, that is to say, that there should be the same distance between their centres ; and, secondly, that they should be at the same height above the rails. If this be not the case, a collision would have the effect of causing one carriage to push the other either aside or upwards, as the case might be ; aside if the centre of the buffer deviated horizontally, and' upwards if it deviated vertically. In any case there would be a tendency of the coaches to throw each other off the rails. The successive coaches forming a train were originally held together by a chain, which was necessarily always a little slack, so that when the power of the engine was driving the train, the buffers were not in close contact, and whenever the train stopped, or even slackened its speed, the hinder carriages ran against the foremost ones with a collision, the force of which was proportional to the difference of their speeds. This mode of connection was replaced by a coupling screw, by means of which the carriages are drawn together, so that the buffers are pressed into close contact, and their springs a little compressed. In this manner the train is formed into one complete column, and the change of speed to which it is subject does not produce the partial collision just mentioned. One of the means, therefore, of diminishing the chances of injuries resulting from collision is to provide against the occur- rence of eccentric buffers, and to ensure the proper coupling of the trains. 175 RAILWAY ACCIDENTS. 34. Although, in most cases of derailment,* it is the engine which escapes from the rails, yet it occasionally happens that while the engine maintains its position, one or more of the carriages forming the train are derailed. This happens frequently when an axle or wheel breaks, but it sometimes happens that a defect of the rail throws a carriage off after the engine and preceding carriages have passed over it. On the 16th September, 1847, on the Manchester and Liverpool Eailway, the last carriage of the express train, having two passengers in it, was derailed, the other carriages being un- disturbed, and was dragged a considerable distance before the engine-driver was made aware of the accident. The two pas- sengers it contained were killed. This accident was ascribed to a defect in the rails. It was supposed that the weight of the engine being too great for the strength of the road, it had deranged the rails in passing over them, and that the succeeding carriages increasing the injury, the displacement only became great enough to derail the wheels on the arrival of the last coach at the point. * We have adopted this word from the French : it expresses an effect which is often necessary to mention, but for which we have not yet had any term in onr railway nomenclature. By deraillement is meant the escape of the wheels of the engine or carriage from the rails ; and the verb to derail or to be derailed may be used in a corresponding sense. 176 RAILWAY ACCIDENTS. CHAPTER II. 1. Necessity of adopting means of watching trains. 2. Proposals of Great Western. 3. Of the North-Western. 4. Merit of engine- drivers. 5. Example in the accident on the Dee. 6. Investigation of circumstances producing accidents arising from imprudence or want of vigilance or care. 7. Instances from reports of railway commissioners. 8. Analysis of 100 accidents produced by impru- dence of passengers. 9. Precautions against accidents. 10. Plain rules for railway travellers to avoid accidents. 11. Not to get in or out while moving. 12. Not to take an unusual position. 13. Stay in your place. 14. Don't get out on wrong side. 15. Don't cross the line. 16. Avoid going in express trains. 17. Avoid special and excursion trains. 18. In case of accident, get out. 19. Don't attempt to recover a falling article. 20. Take the middle carriage. 21. Don't hand an article into a train in motion. 22. Don't sit in your private carriage. 23. Anecdote of Lady Zetland. 24. Beware of level crossings. 25. Avoid night railway travelling. 1. SUCH accidents have suggested to the railway authorities the expediency of adopting some method by which a com- LARPNER'S MUSEUM OF SCIENCE. K 177 No. 12 RAILWAY ACCIDENTS. munication can be made between the several carriages forming the train and the engine-driver. If, in the last instance, the engine-driver had been made aware of the accident at the moment of the derailment, it is probable such fatal results might not have occurred. A case will be mentioned hereafter, in which a private carriage caught fire by a cinder projected from the funnel of the engine falling on its roof. The carriage continued to burn until the arrival of the train at the next station, the engine-driver and conductor being ignorant of the accident. Previously to this, the necessity of some means of watching a train, and of notify ing promptly to the engine-driver the occurrence of any accident, had attracted the attention of the government commissioners, and they consulted some of the principal railway companies on the most desirable means of remedying the evil. 2. The Great Western Company proposed to fix at the back of the tender a seat for a conductor, in a sufficiently high position to see along the roofs of the carriages, so as to have a perfect view of the entire side length of the train, and a means of passing from side to side of the tender, so as to get a view of each side of the train. Such a conductor, from his proximity to the engine, could immediately communicate with the driver, and each guard upon the coaches of the train could communicate with such conductor by signals. 3. The North- Western Company proposed that the under guard should always stand in his van next to the engine, with his face to the train, so as to observe any signal of distress, irregularity, or derangement among the carriages which the chief guard, stationed at the rear of the train, might make. A communication between the under guard and the engineman was only necessary to com- plete this arrangement, and the company accordingly ordered that means should be provided by which the under guard should be enabled at pleasure to open the whistle of the engine. The late Colonel Brandreth had interviews with some of the most eminent railway engineers, with a view to obtain some addi- tional protection for the travelling public, by contriving a method not only for securing the constant watching of the trains while on their journey, but also to provide the passengers with means, in case of accident or sudden illness, of communicating with a guard, and of enabling the guard to communicate with the engineman, for the purpose, when necessary, of stopping the train. There could be no difficulty in providing means by which any passenger could at his pleasure sound the whistle of the engine so as to give the engine-driver notice to stop ; but the govern- ment commissioners considered that it would be objectionable 178 ACCIDENT ON THE DEE BRIDGE. to give a passenger a power to stop the train at will, though it was admitted that it would be extremely desirable to establish a practicable and sure communication between the passengers in each coach with a guard, and to provide the latter with means of communicating with the engine-driver. The great improvements which are made in the application of the electric telegraph justify the expectation that that admirable invention may supply the most effectual means of attaining these objects. Each train might be provided with a portable telegraph, by means of which the passengers in each carriage might have the power of communicating with the principal con- ductor in case of any accident ; while the conductors themselves might be enabled to communicate with each other and with the engine-driver. 4. While noticing the subject of railway accidents arising from causes beyond the control of the passengers, or those who have the management of the trains, it would be an injustice to a most meritorious and generally intelligent class of persons not to acknowledge the zeal, courage, skill, and good conduct of the engine-drivers, conductors, and stokers, as a body. All who have had opportunities of experience in railway transport will feel the justice of such a tribute in the exact proportion of the extent of their experience. Innumerable instances might be offered of admirable judgment and presence of mind exhibited by this class of men in the emergencies which arise in railway travelling. An incident which occurred on the Chester and Holyhead Railway may be mentioned as one among numbers in attestation of this, and in which, although the promptness and presence of mind of the engineer were not successful in effecting the safety of the passengers, they were not the less admirable. 5. On the 24th of May, 1847, a fatal accident occurred to a train in crossing the bridge over the Dee. The train consisted of the engine and tender, weighing 30 tons, followed by three passenger carriages, a luggage-van, and another passenger carriage, containing in all 25 passengers, the gross weight of the train being 60 tons. The train proceeded safely over the first and second arches, and the engine reached the middle of the third arch to a point about 50 feet from the abutments of the bridge. At that point the engine-driver felt the railway sinking under him. With admirable promptitude he instantly opened the steam valve to the fullest extent of its power, giving to the train a sudden pull, so as to endeavour to clear the bridge before the catastrophe, of the imminence of which he was instantly conscious, should occur. His purpose was but partially successful. The engine cleared * 2 179 RAILWAY ACCIDENTS. the bridge as the railway sunk under it, and dragged the tender with it. The fireman, who was upon the tender, was thrown off upon the side of the railway beyond the end of the bridge, and killed. The passenger coaches had not cleared the bridge when it sunk under them, and their connection with the tender was broken. The carriages which had the passengers were preci- pitated into the river from a height of 36 feet above the surface of the water, the depth of which was 10 feet. It appeared afterwards that the tender in following the engine had been derailed, and was dragged along, rubbing hard against the parapet wall at the end of the bridge. It was left standing apart at 50 feet from the water's edge and 3 feet off the rails, the engine having broken away from it, and proceeded with the driver, the only individual who escaped, to the adjacent station. 6. Having investigated the circumstances which produce that class of accidents against which the sufferer cannot effectually protect himself by measures of precaution, it remains now to notice those which arise from imprudence, or from the want of that vigilance and care on the part of the traveller, which the very nature of railway transport renders necessary. 7. The railway commissioners publish periodically reports of all accidents attended with personal injury which take place on railways. The most certain method of ascertaining the manner in which imprudence or negligence operates in the production of these disasters, will be to take from the reports those acci- dents which have occurred to passengers, and to classify them according to their causes. We have accordingly taken indiscri- minately a hundred such occurrences, and have classified them in the following table : 8. Analysis of 100 Accidents produced by Imprudence of Passengers. CAUSES. RESULTS. Killed. Injured. Total. Sitting or standing in improper place, attitude, or position ...... 17 11 28 (retting out of carriage while train in motion . 17 7 24 Getting into carriage while train in motion . 10 6 16 Jumping out to recover hat blown off or parcel dropped 8 5 13 Crossing the railway incautiously . 11 1 12 Getting out on wrong side 3 3 6 Handing an article into a train in motion 1 1 67 33 100 180 CONSEQUENCES OF IMPRUDENCE. 9. From what has been stated and explained, it will be evident that of all the means of locomotion which human invention has as yet devised, railway travelling is the safest in an almost infinite degree. Indeed, the risk to life and limb, when reduced to a numerical statement, seems to be evanescent. Nevertheless the apprehension of danger in this mode of travelling enter- tained by timid persons, and even by some who scarcely merit that appellation, is not inconsiderable. This may arise partly from the circumstance of the public not being generally aware of the smallness of the amount of the danger which has been here described, but in a greater degree from the terrific results of some of the rare accidents which have occurred. In the modes of travelling used before the prevalence of rail- ways, accidents to life and limb were frequent, but in general they were individually so unimportant as not to attract notice, or to find a place in the public journals. In the case of railways, however, where large numbers are carried in the same train, and simultaneously exposed to danger, accidents, though more rare, are sometimes attended with appalling results. Much notice is therefore drawn to them. They are commented on in the journals, and public alarm is excited. Notwithstanding the smallness of the amount of risk, yet, as in many cases the danger of accident beyond the control of the passenger may be diminished by the adoption of proper pre- cautions, and in all cases the causes of danger arising from his own ignorance or neglect may be wholly removed, it may be beneficial to give in a succinct form short rules, by the obser- vance of which the traveller will render still less the amount of that risk already so small. "With this view we have put together the following series of plain intelligible rules, founded partly upon rather a large personal experience in railway travelling in every quarter of the globe where this species of locomotion has been adopted. 10. PLAIN RULES FOR RAILWAY TRAVELLERS. 11. Rule I. NEVER ATTEMPT TO GET INTO OR OUT OF A RAIL- WAY CARRIAGE WHILE IT IS MOVING, NO MATTER HOW SLOWLY. Self-preservation imperiously commands the observance of this rule, since forty in an hundred of the accidents which occur to passengers through their own imprudence, arise from this cause, and of these forty, twenty-seven are fatal. 181 EAILWAY ACCIDENTS. It is a peculiarity of railway locomotion, that the speed, when not very rapid, always appears to the unpractised passenger much less than it is. A railway train moving at the rate of a . fast stage-coach seems to go scarcely as fast as a person might walk. To this circumstance (which is explained by the extreme smoothness of the motion) is to be ascribed the great frequency of accidents arising from passengers attempting to descend from trains while still in motion. On the 4th of July, 1844, on the Dublin and Drogheda Eailway, a passenger jumped out before the train stopped, fell with his hand on the rail, over which the carriage- wheels passed. On the 26th of August, 1844, on the Liverpool and Manchester Eailway, a passenger, jumping out before the train stopped, was killed. Similar accidents fatal to life occurred on the Grand Junction Eailway on the 7th of August, 1846 ; on the Edinburgh and Glasgow, on the 16th of February, 1846 ; on the South- Western, on the 9th of January, 1847 ; on the East-Lanca'ster, on the 29th of May, 1847 ; on the North- Western, on the 1st of February, 1847 ; on the Great North of England, on the 17th of February, 1845 ; on the Midland, on the 27th and 31st of October, 1845. The reports supply an interminable list of like casualties, from which we have taken the preceding indiscriminately. 12. Rule II. NEVER SIT IN ANY UNUSUAL PLACE OR POSTURE. Twenty-eight in every hundred of the accidents to travellers resulting from incaution, arise from this cause, and of these twenty-eight, seventeen are fatal. On some lines of railway seats are provided on the roofs of the carriages. These are to be avoided. Those who occupy them sometimes inadvertently stand up, and when the train passes under a bridge they are struck by the arch. Guards and brakesmen whose duty brings them to these positions, and who are disciplined to exercise caution, are nevertheless frequent sufferers. Passengers should beware of leaning out of carriage windows, or of putting out their arm, or if a second-class carriage, as sometimes happens, has no door, they should take care not to put out their leg. The reports supply frequent examples of fatal accidents from these causes. Outside passengers^ placed on the roof of the car- riages of a train, happening to stand up, were struck on the head by the arches of bridges, at the dates given below on the follow- ing railways : 182 RULES FOR TRAVELLERS. Newcastle and Carlisle , Manchester and Sheffield . North Union South Eastern Bristol and Birmingham Glasgow and Ayr Manchester and Birmingham 2 Sept. 1846. 5 Nov., 1847. 6 Jan. 30 Jan. 1846. 11 July. 16 May, 1844. 31 May, These examples are only a few taken indiscriminately from the reports. The injuries and deaths from leaning out of doors and windows are very numerous, and produced by various causes. On the Preston and Wyre line, on the 18th of April, 1844, a passenger leaning out of a window was struck by the signal board and wounded. On the Bolton and Bury line, on the 26th of July, 1846, a passenger leaning out was struck by the iron column of a bridge, and killed. On the Hull and Selby line, on the 17th of April, 1846, a passenger reaching over to recover his coat had his arm broken. On the Edinburgh and Glasgow line, a passenger, climbing from one compartment of a second class carriage to another, fell and was killed. On the Manchester and Leeds line, a passenger, getting over the side of a carriage instead of going out by the door, fell and was killed. On the Bodmin and Wadebridge line, on the 3rd of August, 1844, a passenger, jumping from one carriage to another, fell between, and was killed. On the Midland line, on the 15th of July, 1846, two passengers, imprudently standing on the seat, were thrown off, and both killed. On the Liverpool and Manchester line, on the 15th of June, 1845, a passenger fell, attempting to pass from one carriage to another, and was injured. On the Grand Junction line, on the 8th of August, 1845, a passenger fell off the buffer of a waggon, and was injured. On the Preston and Wyre line, on the 8th of August, 1845, a passenger, improperly sitting on the side of a carriage, fell off, and was killed. On the York and North Midland line, on the 2nd of November, 1845, a passenger fell from the foot-board of a carriage in motion, aud was killed. On the Dublin and Kingstown line, on the 25th of November, 1845, a passenger, over-reaching herself, fell from a train in motion, and was injured. 183 RAILWAY ACCIDENTS. On the Eastern Counties line, on the 1st of March, 1845, a passenger struck his head against a signal-post while leaning over, and was killed. On the Stockton and Darlington line, on the 14th of April, 1845, a passenger leaning over, struck a waggon, and was injured. On the Dundee and Perth line, on the 24th of July, 1847, a passenger on the roof was struck by a bridge, and killed. On the North-Western line, on the 26th of December, 1847, a passenger was standing upon the step of the tender, after the train got into motion ; and jumping off, was killed. On the Newcastle and Carlisle line, on the 22nd of August, 1847, a passenger got upon the step of a carriage before the train stopped ; fell, and was injured. On the Lancashire and Yorkshire line, June 19, 1848, a passen- ger riding on the roof, contrary to orders, came in contact with a bridge, and was killed. On the South Staffordshire line, on the 8th of July, 1848, a passenger, sitting on the bar of the window, fell out, fracturing leg and head. On the York and North Midland line, on the 28th of August, 1848, a passenger, seated on the edge of an open carriage, lost his balance, and fell between the carriages ; arm broken. 13. Rule III. IT is AN EXCELLENT GENERAL MAXIM IN RAIL- WAY TRAVELLING TO REMAIN IN YOUR PLACE WITHOUT GOING OUT AT ALL UNTIL YOU ARRIVE AT YOUR DESTINA- TION. WHEN THIS CANNOT BE DONE, GO OUT AS SELDOM AS POSSIBLE. 14. Rule IV. NEVER GET OUT AT THE WRONG SIDE OF A RAILWAY CARRIAGE. All who are accustomed to railway travelling know that the English railways in general consist of two lines of rails, one commonly called the up line, and the other the down line. The rule of the road is the same as on common roads. The trains always keep the line of rails on the left of the engine-driver as he looks forward. The consequence of this is, that trains moving in opposite directions are never on the same line, and between these there can never be a collision. The doors of the carriages which are on your right as you look towards the engine open upon the space in the middle of the railway between the two lines of rails. The passenger should never attempt to leave the carriage by these doors ; if he 184 RULES FOR TRAVELLERS. do, he is liable to be struck down or run over by trains passing on the adjacent line of rails. If he leave the carriage by the left-hand door, he descends on the side of the railway out of danger. On quitting a train under such circumstances, immediately retire to the distance of several feet from the edge of the line, so as to avoid being struck by the steps or other projecting parts of carriages passing. On the North- Western Railway, on the ] 2th of January, 1847, a passenger got out at the wrong side, and was run over and killed by a train which was passing at the moment. A like accident happened on the 25th of December, 1848, on the South-Eastern line. The reports abound in like accidents, resulting either in death or broken limbs. 15. Rule V. NEVER PASS FROM ONE SIDE OF THE RAILWAY TO THE OTHER, EXCEPT WHEN IT IS INDISPENSABLY NECESSARY TO DO SO, AND THEN NOT WITHOUT THE UTMOST PRECAUTION. Care should be taken before crossing the line to look both ways, to see that no train is approaching. The risk is not merely that of the train coming upon you before you can pass to the other side. You slip or trip, or otherwise accidentally fall, and a train may be upon you before you can raise yourself and get out of its way. Precaution in this case is especially necessary at a point where the line is carved, and where you cannot command a view to any considerable distance. It is true that the noise of the train generally gives notice of its approach, but this cannot always be depended on, as the wind sometimes renders it inaudible. In crossing a railway at a place where there are sidings and numerous points (which is always the case at and near stations), the feet are liable to be caught between the rails and points, and in such cases it has happened very frequently that the person thus impeded is run over by a train before he is able to dis- engage himself. Passengers waiting at stations for the arrival of a train, or having descended from a train which has stopped and waiting to remount, stand in need of the greatest caution. The refresh- ment-room is sometimes on the side of the road, opposite to that on which the train stops, in which case it can only be arrived at by crossing the Hue. The reports abound in cases showing the necessity of observing this rule. On the 29th of June, 1846, a female passenger on the 185 RAILWAY ACCIDENTS. Brighton Kail way waiting for a train, was crossing the railway, and fell, it is supposed with fright, on seeing the train approach- ing. The station-clerk, on perceiving her situation, hurried to her assistance, and while endeavouring to remove her, the train went over and killed both. On the 26th of March, 1847, a passenger on the York and Newcastle railway, in crossing the line, had his foot caught bet ween the points, and was held fast there, until a train arriving passed over and killed him. On the 8th of May, 1846, a lady, on the Eastern Counties railway, attempting to cross the line, in order to prevent one of her children getting upon it from the opposite side, was run over and killed. On the Darlington Eailway, on the 15th of June, 1846, a passenger, waiting for a train, fell asleep on the edge of the platform, and was struck by a goods train passing and killed. It frequently happens that while the attention of a person crossing a line is directed to a train approaching from one direction which he thinks there is time to avoid, he is run over by a train, from which his attention has been withdrawn, coming from the opposite direction. This occurred for example on the Caledonian railway, on the 15th of March, 1847, when a passenger was run over by a train while his attention was directed to another train coming from the opposite direction. Similar accidents, attended with a like result, are recorded of numerous other lines. On the 30th of December, 1847, a passenger, on the Midland line, having left the train and attempted to cross the line, was crushed by the step of the brake- van against the platform and killed. 16. Rule VI. EXPRESS-TRAINS ARE ATTENDED WITH MORE DANGER THAN ORDINARY TRAINS. THOSE WHO DESIRE THE GREATEST DEGREE OF SECURITY SHOULD USE THEM ONLY WHEN GREAT SPEED IS INDISPENSABLE. The principal source of danger for express-trains arises not so much from their extreme speed as from their rate of progress being different from that of the general traffic of the line. If all trains without exception moved with exactly the same speed, no collision by one overtaking another could occur. The more they depart from this uniformity the more likely are collisions. Now the speed of express-trains is both exceptional and extreme. Inasmuch as it is exceptional, they are likely to overtake the slower and regular trains, if these be retarded even in the least 186 RULES FOR TRAVELLERS. degree by any accidental cause ; and inasmuch as it is extreme, they are more difficult to be stopped in time to prevent a collision in such a contingency. If a collision occur, the effects are disastrous, in the direct ratio of the relative speed of the trains, one of which overtakes the other. The momentum of the shock, other things being the same, will be proportional to the excess of the speed of the faster over that of the slower train. The "probability of a collision will also be increased in the same ratio. To work express trains with safety, an additional line of rails should be laid down and appropriated to them. Their number per day being necessarily small, and the duration of their trips short, the same line of rails might, without inconvenience or danger, serve for the traffic in both directions as on single lines of railway. Examples illustrative of the danger attending express- trains abound in the reports. The following may be men- tioned : On the Great- Western, on the 10th of May, 1848, six pas- sengers were killed, and thirteen injured, in consequence of a train coming in collision with a horse-box at the Shrivenham station. On the Lancaster and Preston, on the 21st of August, 1848, one passenger was killed, and two seriously injured, in conse- quence of a collision at the Bay Horse station between a Lancaster and Carlisle Company's express-train, and a local train belonging to the Lancaster and Preston Company. On the North-Western, on the 2nd of September, 1848, an express-train ran off the rails near the Newton Road station, causing severe injury to two passengers, Mr. Shuard and Colonel Baird, both of whom died afterwards. On the South- Western, on the 17th of November, 1848, an express-train ran into a ballast-engine on the Richmond line, causing death to one servant of the company and injury to four others, all of whom were riding on the engine ; also injury to eight passengers in the express-train. 17. Rule VII. SPECIAL TRAINS, EXCURSION TRAINS, AND ALL OTHER EXCEPTIONAL TRAINS ON RAILWAYS ARE TO BE AVOIDED, BEING MORE UNSAFE THAN THE ORDINARY AND REGULAR TRAINS. There is always more or less danger of collision when any object on a railway is out of its customary place. The engine-drivers of the regular trains are always informed of 187 JJAILWAY ACCIDENTS. the course of other regular trains, and, except in cases of accidental stoppage or delay, they know where they are liable to be encountered. Special trains are supplied on sudden and unforeseen occasions, and although their drivers are informed of the movement of the regular trains, and may therefore provide against collisions, this information is not reciprocal. Excursion trains are exceptional but not unforeseen, and are not therefore as unsafe as special trains. They are, nevertheless, to be avoided by those who scrupulously consult their safety. An examination of the statistics of accidents would conclusively prove the prudence of such a course. On the Maryport and Carlisle, on the 10th of November, 1846, a collision between a special train and a coal-train took place in consequence of neglect on the part of the signal-man at the Wigton station, and of the agent and superintendent of locomotives at Carlisle, in not informing the driver of the coal-train that a special train was expected, and that he was not to start until it arrived. Engine-driver and sole passenger injured. 18. Rule VIII. IF THE TRAIN IN WHICH YOU TRAVEL MEET WITH AN ACCIDENT, BY WHICH IT IS STOPPED AT A PART OF THE LINE, OR AT A TIME, WHERE SUCH STOPPAGE IS NOT REGULAR, IT IS MORE ADVISABLE TO QUIT THE CARRIAGE THAN TO STAY IN IT, BUT IN QUITTING IT REMEMBER RULES I., IV., AND V. It may be affirmed generally that there is always more or less danger on a railway when carriages or waggons are found at a place, where in the regular working of the line, they ought not to be. In such cases a train following them, not expecting to find them there, is likely to run upon them and produce a collision. We have personally witnessed more than one example of this, and the reports of the railway commissioners supply several. "We should therefore recommend the above rule for general observ- ance ; but in leaving the train passengers should beware of crossing the line, or standing on it, or of getting out of the carriages at the wrong side. On the South- Western, on the 14th of January, 1848, the engine of a passenger train having been partially disabled, the engine-driver got under it to repair the damage. While thus employed, a goods train overtook and ran into the passenger train, causing the instant death of the driver, and injury to the fireman and eleven passengers ; also injury to one of the guards of the goods train. 188 RULES FOR TRAVELLERS. On the Manchester and Leeds, on the 9th of March, 1847, a passenger train was stopped by a broken axle ; another train belonging to the Manchester and Leeds Railway Company, not- withstanding signals were made, ran into and injured the two hindmost carriages. On the Midland, on the 20th of October, 1845, a pilot-engine, sent after a disabled passenger train to assist it, overtook and ran into it. Two passengers killed. 19. Rule IX. BEWARE OF YIELDING TO THE SUDDEN IMPULSE TO SPRING FROM THE CARRIAGE TO RECOVER YOUR HAT WHICH HAS BLOWN OFF, OR A PARCEL DROPPED. It would appear that there is an impulse, which in some individuals is almost irresistible, to leap from a train to recover their hats when blown off or accidentally dropped. The reports of railway accidents supply numerous examples of this. On the Edinburgh and Glasgow, on the 2nd of December, 1846, a passenger fell between carriages in motion, while attempting to recover his cap, which had been blown off into the next carriage, and was killed. On the Manchester and Birmingham, on the 16th of October, 1845, a passenger was struck by a bridge while getting on the roof of oiie of the carriages to recover his hat which had been blown off, and was killed. On the Manchester and Leeds, on the 23rd of January, 1845, a passenger, attempting to recover his hat, fell off the train and was killed. On the North- Western, on 26th of June, 1847, a passenger, jumping after his hat from a train in motion, was killed. On the same line, on the 10th of May, 1847, a passenger, jump- ing after his hat from a train in motion, fell upon a block of stone, and was killed on the spot. 20. Pade, X. WHEN YOU START ON YOUR JOURNEY, SELECT, IF YOU CAN, A CARRIAGE AT OR AS NEAR AS POSSIBLE TO THE CENTRE OF THE TRAIN. In case of collision, the first and the last carriages of a train are the most liable to damage. If the train run into another, the foremost carriages suffer. If it be run into by a train over- taking it, the hindmost carriages suffer. Almost every case of collision affords an example illustrating this rule. In case of the engine running off the rails, the carriages most likely to suffer are the foremost. 189 EAILWAY ACCIDENTS. 21. Rule XI. Do NOT ATTEMPT TO HAND AN ARTICLE INTO A TRAIN IN MOTION. On the London and Brighton railway, on the loth of February, 1847, a passenger, while handing a basket to the guard of a passing train, had his coat caught by one of the carriages, and was dragged under the wheels and killed. 22. Rule XII. IF YOU TRAVEL WITH YOUR PRIVATE CARRIAGE, DO NOT SIT IN IT ON THE RAILWAY. TAKE YOUR PLACE BY PREFERENCE IN ONE OF THE REGULAR RAILWAY CARRIAGES. The regular railway carriages are safer in case of accident than a private carriage placed on a truck. They are stronger and heavier. They are less liable to be thrown off the rails, or to be crushed or overthrown in case of a collision. The cinders ejected from the smoke funnel of the engine are generally in a state of vivid ignition, and if they happen to fall on any com- bustible object, are liable to set fire to it. The railway carriages are constructed so as to be secured from such an accident, but private carriages are not so, and, moreover, from their greater elevation, when placed on a truck, are more exposed. Serious accidents have sometimes occurred from this cause. The trucks which carry private carriages are also often placed at the end of the train, the least safe position. (See Rule X.) 23. On the 8th Dec., 1847, an accident happened to the Countess of Zetland, while travelling in her private carriage on the Midland Eailway, of which Lady Zetland herself gave the following narrative. The accident occurred about 5 o'clock in the afternoon, as the train was approaching Eugby from Derby, en route to London, and at about six miles from Eugby. "Aske, Richmond, Yorkshire. " On the 8th of December, I left Darlington by the 9h. 25m. train for London. I travelled in my chariot with my maid. The carriage was strapped on to a truck, and placed with its back to the engine, about the centre of the train, which was a long one. Soon after leaving Leicester, I thought I smelt something burning, and told my maid to look out of the window on her side to see if anything was on fire. She let down the window, and so many lumps of red-hot coal or coke were showering down that she put it up again immediately. I still thought I smelt something burning ; she put down the window again, and exclaimed that the carriage was on fire. We then put down the side-windows, and waved our handkerchiefs, screaming fire ' as loud as we could. No one took any notice of us. I then pulled up the windows, lest the current of air through the carriage 190 RULES FOR TRAVELLERS. should cause the fire to burn more rapidly into the carriage, and determined to sit in as long as possible. After some time, seeing that no assistance was likely to be afforded us, my maid became terrified, and without telling me her intention, opened the door, let down the step, and scrambled out on to the truck. I followed her, but having unluckily let myself down towards the back part of the carriage, which was on fire, was obliged to put up the step and close the door as well as I could, to enable me to pass to the front part of the carriage, furthest from the fire, and where my maid was standing. We clung on by the front springs of the carriage, screaming 'fire' incessantly, and waving our hand- kerchiefs. We passed several policemen on the road, none of whom took any notice of us. No guard appeared. A gentleman in the carriage behind mine saw us, but could render no assist- ance. My maid seemed in an agony of terror, and I saw her sit down on the side of the truck and gather her cloak tightly about her. I think I told her to hold fast to the carriage. I turned away for a moment to wave my handkerchief, and when I looked round again my poor maid was gone. The train went on, the fire of course increasing, and the wind blowing it towards me. A man (a passenger) crept along the ledge of the railway carriages, and came as near as possible to the truck on which I stood, but it was impossible for him to help me. At last the train stopped at the Eugby station. An engine was sent back to find my maid. She was found on the road, and taken to the Leicester Hospital, where she now lies in an almost hopeless state ; her skull fractured ; three of her fingers have been ampu- tated. I am told the train was going at the rate of fifty miles an hour. "S. T. ZETLAND." The train, consisting of seven passenger carriages, two brake- vans, and four private carriages on trucks, altogether thirteen separate carriages, was drawn by an engine with driver and fireman, and was under the charge of one guard, who was placed in the rear of the entire train, and within a luggage-van, from which it was impossible for him to see the burning carriage, which was the eighth from the engine. 24. Rule XIII. BEWARE OF PROCEEDING ON A COACH ROAD ACROSS A RAILWAY AT A LEVEL CROSSING. NEVER DO SO WITHOUT THE EXPRESS SANCTION OF THE GATEKEEPER. On the English railways, common roads are usually carried over or under the railway, which is crossed by or crosses them by bridges. This, however, is not invariable, and the greatest 191 . RAILWAY ACCIDENTS. caution should be observed in passing such, level crossings. A restive horse has frequently produced injurious or fatal accidents in such cases. 25. Rule XIV. WHEN YOU CAN CHOOSE TOUR TIME, TRAVEL BY DAY RATHER THAN BY NIGHT ; AND IF NOT URGENTLY PRESSED, DO NOT TRAVEL IN FOGGY WEATHER. Accidents from collision and from encountering impediments accidentally placed on the road happen more frequently at night and in foggy weather, than by day and in clear weather. / Persons on or near railways appear to be sometimes seized with a delirium or fascination which determines their will by an ^irresistible impulse to throw themselves under an approaching train. Cases of this kind occur so frequently, and under such circumstances, as cannot be adequately explained by predis- position to suicide. Examples. On the Midland railway, on June 20, 1845, a plate-layer jumped suddenly in front of a train in motion ; no cause can be assigned. On June 25, 1845, a trespasser ran from behind a bridge, and laid himself across the rails in front of an approaching train. On September 18, 1845, a trespasser laid his neck on the rail in front of an approaching train ; supposed to be insane. On the South- Western railway, on June 9, 1847, Frances Arney threw herself under the wheels of a train ; killed. On the Glasgow and Paisley railway, on November 19, 1847, a woman of dissipated habits rushed from the side of the railway, and throwing herself in front of an approaching train, was run over and killed. On the South- Western railway, on February 19, 1848, a person committed suicide by placing himself before an approaching train. On the Sheffield and Manchester railway, on May 4, 1846, a person committed suicide by laying himself across the rails in front of an approaching train. 192 LIGHT. 1. Description of eye, and mode in which light is transmitted to it Ways in which objects are rendered visible. 2. Analogy between the eye and the organ of smelling. 3. Analogy between the eye and the'ear. 4. Luminiferous ether. 5. Corpuscular theory Undulatory theory. 6. Undulatory theory explained and examined Roemer's discovery of the velocity of light Newton's solution of the amplitude or breadth of the luminous waves Altitude of luminous waves Table of the magnitudes of the luminous waves of each colour. 7. Consideration of the two theories of light. 8. The idea of the undulatory theory enter- tained by Descartes, Hooke, and others The honour of having re- duced the hypothesis to a definite shape attributable to Huygens Dr. Young's mechanical reasoning thereon. 9. Malus discovers the polarisation of light by reflection The theory greatly extended by Fresnel, Arago, Poisson, Herschel, and others. 10. Relation of light and heat Herschel's discovery apparently establishing the inde- pendence of the heating and illuminating effects of the solar rays Berard's experiments. 11. Bodies luminous and non-luminous. 12. Transparency and opacity. 1. AMONG the many marvellous results of the labours of the human mind directed to the discovery of the laws of the physical creation, there is perhaps none which strikes us with more astonishment than the knowledge which has been obtained relating to the qualities and laws of LIGHT. I propose for the present to bring forward the facts which have been disclosed regarding its physical nature and its motion through space, as LARDNEB'S MUSEUM OF SCIENCE. o 193 No 13. LIGHT. well as the manner in which it affects the organ of vision, so as to produce the perception of external and distinct objects. Between the eye and any distant object, there intervenes a space of greater or less extent, and often, as in the case of the stars, so great as to be incapable of being clearly and adequately expressed by any standard or modulus of magnitude with which we are familiar. Yet objects, at these immense distances, are rendered visible to us by some physical effects which they produce upon our organs of vision. It has been ascertained that the interior of the e} r e-ball is lined with a membrane highly susceptible of mechanical vibration and connected by a continuity of nerves with the brain ; and to this membrane admission is given to light by an opening in front of the eye called the pupil. The light then proceeding from any distant object must be supposed to pass over the space intervening between the object and the eye, to enter the pupil and to produce upon the membrane within the eye a specific mechanical effect, which being propagated to the brain, is the means of producing in the mind a perception of the distant object. How then are we to conceive that an object placed at any distance, for example, say one hundred millions of miles, from the eye, can transmit over and through that space a mechanical effect on the eye ? We answer that there are two, and only two, ways in which it is possible to conceive such an action to take place. These two are the following : First. The distant object thus visible to us, may emit particles of matter from its surface, which particles of matter may pass over the intervening space, may enter the pupil of the eye, may strike upon the nervous membrane, and so affect it as to produce vision. Secondly. There may be in the space between the distant visible object and the eye, a medium possessing elasticity, so as to be capable of receiving and transmitting pulsations or undu- lations like those imparted to the air by a sounding body. If this be admitted, the distant visible object may, without emitting any particles of matter from its surface, affect such a medium surrounding it with pulsations or undulations, in the same manner as a bell affects the air around it. These pulsations or undulations may pass along the space intervening between the visible object and the eye, in the same manner as the pulsations or undulations produced by a bell pass along the air between the bell and the ear. In this manner, the pulsations transmitted from the visible object, and propagated by the medium we have referred to, may reach the eye and affect the membrane which lines it, in the same manner exactly as the pulsations in the air affect the tympanum of the ear. 194 THEORIES OF LIGHT. These are the two, and the only two modes, in which it was ever imagined that a distant object could become visible to the eye. 2. In the first, there is an analogy between the eye and the organs of smelling. Odorous objects do actually emit material effluvia, which form part of their own substance. These effluvia reach the organ of smelling, and produce upon it a specific effect, which impresses the mind with a corresponding perception. According to the first supposition, a visible object at any distance would act in the same way, and would eject continual particles of light, which particles of light would move to the eye and produce vision, acting mechanically on its membrane in the same manner as the effluvia of a rose produce a sensible eifect upon the organs of smelling. 3. The second method places the eye in analogy with the ear. So close is this analogy, that all the mathematical formulae by which the effects of sound are expressed in acoustics, will, with very slight changes, be capable of expressing the effects of vision, according to the latter hypothesis. 4. It is evident, however, that as the first hypothesis requires us to admit that distant visible objects are continually ejecting matter from their surfaces to produce vision ; so the second hypothesis as peremptorily requires the admission of the existence of some physical medium pervading the universe, some subtle ethereal fluid endowed with a property of propagating the pulsa- tions or undulations of distant visible objects, and transmitting them to the eye. This hypothetical fluid has been called the luminiferous ether. 5. The first of these two celebrated theories of light has been called the CORPUSCULAR THEORY, and the second the UNDULATORY THEORY. Newton, although he did not identify his investigations in optics with any hypothesis, but in the spirit of the inductive philosophy founded by Bacon based his conclusions on experi- ments and observations only, adopted nevertheless the nomen- clature and language of the corpuscular theory, and, probably, from veneration for his authority, English philosophers, until recently, have very generally given the preference to that theory. The undulatory theory, on the other hand, was adopted by Huygens, and after him by most continental philosophers. Optical researches within the last hundred years have been prosecuted with singular diligence and success. A vast variety of phenomena previously unknown, have been accurately investi- gated, new laws have been developed, and the general result has been that the undulatory theory has prevailed over the corpus- o 2 195 LIGHT. cular. It is perhaps not an unfair statement of the actual condition of these two celebrated hypotheses, to say that while the corpuscular system is found sufficient to explain most of the common and obvious phenomena of optics, it totally fails in explaining many of the most remarkable effects brought to light- by modern observations and experiments. On the other hand, the undulatory theory in general offers a satisfactory expla- nation for all. This circumstance has very properly and legiti- mately enlisted under that hypothesis almost all the leading scientific men of the present day. Although the principal facts which we shall have now to explain are in fact independent of either of these two hypotheses, and incontestably true, whichever may be adopted, yet in their exposition it will be necessary to adopt the language of one or the other of these theories. We shall, for the reason just stated, use the nomenclature of the undulatory theory. "We are then to imagine light to consist of undulations propa- gated through the universal ether, in the same manner as the waves or undulations of sound are propagated through the air. 6. The first question then that arises is, what is the velocity with which these waves move ? At what rate does light come from a distant star to the eye ? Is it propagated instantaneously 1 Would a fire suddenly lighted at a point one hundred millions of miles from the eye be seen at the moment the light was pro- duced 1 or would an interval of time be necessary to allow the light to reach the eye ? and if so, what would be the interval of time in relation to the distance of the luminous object ? In tracing the progress of human knowledge, we frequently have occasion to behold with surprise, and not without a due sense of humility, the important part which accident plays in the advancement of science. Often are we with diligent zeal in search of things, which, if found, would be of trifling or no value, when we stumble on inestimable treasures of truth. The frequency of this strongly impresses the mind with the persuasion that there is in secret operation a power whose will it is that knowledge and the human mind should be constantly progressive. It is in physics as in morals. We ignorantly seek that which is worthless, and find what is inestimable. In the pursuit of knowledge we might well say that which we are taught to express in the pursuit of what is moral and good. We might say that the power which governs its progress knows better than we do "our necessities before we ask, and our ignorance in asking." We shall see a striking example of this in the narrative of the celebrated discovery of the motion of light. Soon after the invention of the telescope, and the consequent 196 ITS VELOCITY. discovery of Jupiter's satellites, Roemer, an eminent Danish astronomer, engaged in a series of observations, the object of which was the discovery of the exact time of the revolution of one of these bodies around Jupiter. The mode in which he proposed to investigate this, was by observing the successive eclipses of the satellite, and noticing the time between them. Let s (fig. 1) represent the sun, and A B c D E F G H the successive relative positions of the earth. Let j be Jupiter projecting behind him his conical shadow, and let M is represent the orbit of one of his satel- lites. After each revolution the satellite will enter the shadow at M, and emerge from it at N. Now if it were possible to observe accurately the moment at which the satel- lite would, after each revolution, either enter the shadow, or emerge from it, the interval of time between these events would enable us to calculate exactly the velocity and motion of the satellite. But by attentively watching the satellite we can note the time it enters the shadow, for at that moment it is deprived of the sun's light, and becomes invisible. We can also note the moment of its emer- gence, because then escaping from the edge of the shadow, it comes into the sun's light, and becomes visible. It was in this manner that Roemer proposed to ascertain the motion of the satellite. But in order to obtain the estimate with the greatest possible precision, he proposed to continue his observations for several months. Let us, then, suppose that we have observed the time which has elapsed between two successive eclipses, and that this time is, for example, forty-three hours. We ought to expect that the eclipse would recur after the lapse of every successive period of forty-three hours. Imagine a table to be computed in which we shall calculate and register beforehand the moment at which every successive eclipse of the satellite for twelve months to come shall occur, we 197 LIGHT. shall then, as Boemer did, observe the moments at which the eclipses occur and compare them with the moments registered in the table. Let the earth be supposed at A, at the commencement of these observations, where it is nearest to Jupiter. When the earth has moved to B, which it will do in about six weeks, it will be found that the occurrence of the eclipse is a little later than the time registered in the table. When the earth arrives at c, which it will do at the end of three months, it will occur still later than the registered time. In fact, at c the eclipses will occur about eight minutes later than the registered time. At D they will be twelve minutes later, and at E sixteen minutes later. By observations such as these, Eoemer was struck with the fact that his predictions of the eclipses proved in every case to be wrong. It would at first occur to him that this discrepancy might arise from some errors of his observations ; but if such were the case, it might be expected that the result would betray that kind of irregularity which is always the character of such errors. Thus it would be expected that the predicted time would sometimes be later, and sometimes earlier than the observed time, and that it would be later and earlier to an irregular extent. On the contrary, it was observed during an interval of little more than six months which the earth took to move from A to E, that the observed time was continually later than the predicted time, and moreover, that the interval by which it was later continually and regularly increased. This was an effect too regular and consistent to be supposed to arise from the casual errors of observation ; it must have its origin in some physical cause of a regular kind. The attention of Eoemer being thus attracted to the question, he determined to pursue the investigation by continuing to observe the eclipses for another half year. Time accordingly rolled on, and the earth transporting the astronomer with it, moved from E to r. On arriving at F, and comparing the observed with the predicted eclipse, it was found that the observed time was now only twelve minutes later than the pre- dicted time. Soon after the expiration of the ninth month when the earth arrived at G, the observed time was found to be only eight minutes later ; at H it was only four minutes later, and finally, when the earth returned to its first relative position with the planet, the observed time corresponded precisely with the predicted time.* From this course of observation and inquiry it became * The exact interval is 398 days, the synodic period of Jupiter. 198 ITS VELOCITY. apparent that the lateness of the eclipse depended altogether on the increased distance of the earth from Jupiter. The greater that distance, the later was the occurrence of the eclipse as apparent to the observers, and on calculating the change of distance, it was found that the delay of the eclipse was exactly proportional to the increase of the earth's distance from the place where the eclipse occurred. Thus when the earth was at E, the eclipse was observed 16 minutes, or about 960 seconds later than when the earth was at A. The diameter of the orbit of the earth, A E, measuring about 190 millions of miles, it appeared that that distance produced a delay of 960 seconds, which was at the rate of 198,000 miles per second. It appeared, then, that for every 198,000 miles that the earth's distance from Jupiter was in- creased, the observation of the eclipse was delayed one second. Such were the facts which presented themselves to Koemer How were they to be explained ? It would be absurd to suppose that the actual occurrence of the eclipses was delayed by the increased distance of the earth from Jupiter. These phenomena depend only on the motion of the satellite and the position of Jupiter's shadow, and have nothing to do with, and can have no dependence on the position or motion of the earth, yet unquestion- ably the time they appear to occur to an observer upon the earth, has a dependence on the distance of the earth from Jupiter. To solve this difficulty, the happy idea occurred to Koemer that the moment at which we see the extinction of the satellite by its entrance into the shadow is not, in any case, the very moment at which that event takes place, but sometime after- ward, viz. : such an interval as is sufficient for the light which left the satellite just before its extinction to reach the eye. Viewing the matter thus, it will be apparent that the more distant the earth is from the satellite, the longer will be the interval between the extinction of the satellite and the arrival of the last portion of light which left it, at the earth ; but the moment of the extinction of the satellite is that of the com- mencement of the eclipse, and the moment of the arrival of the light at the earth is the moment the commencement of the eclipse is observed. Thus Roemer with the greatest felicity and success explained the discrepancy between the calculated and the observed times of the eclipses ; but he saw that these circumstances placed a great discovery at his hand. In short, it was apparent that light is propagated through space with a certain definite speed, and that the circumstances we have just explained supply the means of measuring that velocity. We have shown that the eclipse of the satellite is delayed one 199 LIGHT. second more for every 198,000 miles that the earth's distance from Jupiter is increased, the reason of which obviously is, that light takes one second to move over that space ; hence it is apparent that the velocity of light is at the rate, in round numbers, of 200,000 miles per second. Such was the discovery which has conferred immortality upon the name of Koemer ; a discovery to which, as we have shown, he was accidentally led when seeking to determine the velocity of one of the moons of Jupiter. The velocity of light thus determined would, in the corpuscular theory, be regarded as that with which the particles of light issuing from the surface of a visible object move through space. In the undulatory theory, however, which is more generally received, this velocity is that with which the waves are propagated through space, in the same sense as waves appear to move on the surface of water if a pebble be dropped in to form a centre round which they are propagated. It is necessary to remember when considering any system of undulations, no matter through what medium they may be pro- pagated, that the progressive motion which belongs to them is a motion of form merely, and not of matter. The waves which are propagated round a centre when a pebble is dropped into calm water, present an appearance to the eye as though the water which formed the wave really moved outward from the centre of the undulations. Such is, however, not the case. No particle of the fluid has any progressive motion whatever, of which many proofs may be offered. If any floating body be placed on the surface of the water, it will not be carried along by the waves, and if similar waves be formed, as they might be, by giving a peculiar motion to a sheet or cloth, they would have the same appearance of progressive motion, although the parts of the sheet or cloth, as is evident, would have no other motion than the up- and-down motion that would form the apparent undulations. The waves of the sea appear to the eye to be endowed with a progressive motion. A slight reflection, however, on the con- sequences of such a motion, will soon convince us that it can have no reality. The. ship which floats upon the waves is not carried forward with them ; they pass beneath her, now lifting her on their summits, and now letting her sink into the abyss between them. Observe a sea-fowl, or a nautilus floating on the water, and the same effect will be presented. If, how- ever, the water itself partook of the motion as well as its waves, the ship and the fowl would be carried forward in the direction of that motion. Once on the summit of a wave, there they would continually remain, and their motion would 200 ITS UNDULATIONS. be as smooth as if they were propelled on the calm surface of a lake. We are then to remember that when light is propagated through space with the astonishing velocity of 200,000 miles per second, there is no material substance which really has this progressive velocity ; it belongs merely to the form of the pulsa- tions, or undulations. The same observations, exactly, are appli- cable to the transmission of the waves of sound through the air. In order to submit the phenomena of light to a strict physical analysis, it is not enough to measure the motion of its waves. We require also to know their amplitude or breadth, just as, in the case of the waves of the sea, we should require to know not only the rate at which they are propagated over the surface of the water, but also the space which intervenes between the hollow or crest of each and the hollow or crest of the succeeding one. For the solution of this problem we are indebted to Newton himself. To render intelligible the mode in which he solved it, let us imagine a flat plate of glass, such as D E (fig. 2), placed upon a convex lens of glass, the surface of which is represented by A E, but which must be supposed to have infinitely less curvature than that which appears in the figure. D c a Fig. 2. C E The under surface of the flat plate will touch the vertex ot the convexity at c, and the further any point on the under surface is from c, the greater will be the distance between the surfaces of the two glasses. Thus the distance between them at a is less than at c, and the distance at c is less than at AY, EXPLANATORY OF THE SYSTEM. 12mo. 6