E 3\facfad Ernest Sa Ttmversi Chfiri THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES Ex Libris SIR MICHAEL SA ACQUIRED 194 WITH THE HELP OF ALUM SCHOOL OF EDUCA SUGGESTIVE HINTS TOWARDS IMPROVED SECULAR INSTRUCTION, MAKING IT BEAR TTPON PRACTICAL LIFE: INTENDED FOR THE USE OF SCHOOLMASTERS AND TEACHERS IN OUR ELEMENTARY SCHOOLS, FOR THOSE ENGAGED IN THE PRIVATE INSTRUCTION OF CHILDREN AT HOME, AND FOR OTHERS TAKING AN INTEREST IN NATIONAL EDUCATION. BY EICHARD DAWES, A.M., DEAN OF HKBEFOBD. "MEWS SIBI CONSCIA EECTi." Virg, A GOOD INTENTION. (Ebitiutt, LONDON: GEOOMBEIDGE AND SONS, 5, PATERNOSTER ROW. LONDON: IHOKAS HAKBILD, FLEBT ST8CKI. .uage LS *"** CONTENTS. PAGT. IJJTHODUCTION . xv Introductory remarks 1. Grammar . . *. 9 Poetry 16 Questions on materials of food, clothing, etc. . . 23 Exercises for children to write on their slates at school, and on paper in the evening ... 28 Geography 30 Physical Geography . . . . 40 Natural History . 44 English History '. 46 Arithmetic 48 Algebraic formula 50, 57 Questions on the economic purposes of life . 52, 56 Solid measure ...... 59 Examples for practice . . , . . 64 Geometry 66 Diagrams 70, 71 Land measuring 73 Words ending in ometry and ology . . 74 Elementary drawing 75 Mechanics 80 Natural Philosophy 86 Experiments 88 Barometer ....... 90 Specific gravity . . . ' * 92 Table of the velocity and force of the wind . 93 Questions . . 94 Experiments . 98 Metals . .106 Experiments. . .. . . . . 115 Light 130 Astronomy . . . '. . ' . . . 138 Eclipses . 146 Chemistry .148 CONTENTS. A knowledge of common things Sources of domestic health and comfort Knowledge of mechanic's and labourer's work Explanation of natural phenomena Geology Statistics ......... Value of labour in manufactured products . Conversational Lectures ...... A loaf of bread The cottage fire Singing ......... Observations on the duties cf a schoolmaster Concluding remarks. State of the cottages of the poor. Mr. Justice Coleridge's opinion. Ignorance of the rural districts. On wages . The Arithmetical Constants TABLE. 1. Numerical Constants 2. Time of light travelling 3. Specific gravity ....... 4. Barometrical height, and corresponding tempera- ture at which water boils 5. Melting points of different substances . 6. Boiling points of different liquids .... 7. Freezing points of liquids 8. Linear dilatation ....... of solids by heat of liquids by heat 9. Latitude and longitude, etc., of different places, and mean temperature of the seasons A list of some of the philosophical and other apparatus used in the school PREFACE. THE. reader must not expect anything like perfection in the following pages, or that the matter which they contain is arranged in the best possible order; they are intended to give an idea of what is taught in the school here, and the manner of teaching it : the Author feels that if anything of this kind had fallen in his own way when this school opened, it would have saved him much trouble ; however, without apologizing for their imperfections, or attempting to point out their merits (the former of which others will but too readily see), such as they are, " he casts his bread upon the waters," hoping that it may in some way or other advance the cause of education : there will, no doubt, be found in it some chaff, but not unmixed, he is willing to hope, with some wheat also, which may be worth picking out : on the whole, as the man who purchased an axe of the blacksmith, which he wished to have all over polished like the edge, to which the latter agreed on condition that he would turn the grindstone, but finding the labour of so doing greater than he expected, said, he was not quite sure that he did not prefer a speckled axe to a bright one ; so I feel myself obliged to let ray axe go forth with many specks upon it ; however, such as it is, take it, reader ! profit from, the bright spots, if it has any, and be lenient to the specks. KING'S SoMBORNa, April 18, 1847. PREFACE TO THE SEVENTH EDITION. A NEW Edition of this little work having been called for, i avail myself of the opportunity of adding a few remarks on subjects of interest, arising out of the altered and vary- ing conditions of our educational wants, and which are given in this prefatory chapter, as being the most conve- nient form in which to give them. The observations in former editions on the supply of books to schools by the Committee of Council are omitted, the conditions on which grants are now made rendering them unnecessary, and a new book list, with the altered conditions, has been lately issued ; also a revised list of scientific apparatus for the use of elementary schools, with b IV PBEFACK. a special report, by the Rev. F. Temple, Her Majesty's Inspector of Training Schools. The changes which have taken place in regulating the admission of persons to the civil service of the crown, and the adoption of an educational test for all the lower offices, and of limited competition for some, might also seem to render it unnecessary to continue the remarks on this subject; but I have allowed them to remain, as they are brief, and, in some measure, sho\v the progress of opinion which has led to this important change. A Board of Commissioners, under whom the necessary examinations are conducted, has been in operation for some time, and their report laid before Parliament last Session, . ought to be in the hands of all schoolmasters and others in- terested in the education of youth ; not from its pointing out the way to Government situations, but from its showing what are the useful and necessary educational requirements for business life, whether in the civil service of the country or in general commerce. This Report, to which I have written a preface, has been reprinted in a cheap form, by Messrs. Groombridge and Sons, in order to facilitate its circulation as widely as possible. ' It contains tabular statements of the requirements for the various offices in the different departments of the public service limits of age between which candidates are admissible, etc., with other information interesting to the public at large. Educational tests, as passports to employment, are not only necessary in the departments of the Civil Service of the Crown, but there is also a growing feeling in favour of them in mercantile life, when good writing, correct spelling, and a good knowledge of arithmetic are important requisites. As a proof of this, when the Society of Arts were about to establish a system of examination of members of Mechanics' Institutes in connection with them, giving certificates of proficiency to deserving candidates after examination, a declaration of confidence in such certifi- cates and of attaching a value to them as n commendations to employment, was signed by a large number of the leading commercial firms and employers of labour in different parts * " Manual of Educational Acquirements necessary for the Civil Service," etc. Messrs. Groombridge and Sons. Price 8rf. PKEFACE. T of the countiy, and by many of our most eminent scientific men ; thus giving a commercial value to education, as well as a moral one, which when once generally recognized by all classes of society will settle the education question. The first examination took place last June, and the results in every way justified the expectations of those who established it. A similar examination is intended for this year, both in London and at Huddersfield ; audit is much to be regretted that the Council declined to comply with the request of the Hants and Wilts Association to extend the sume benefit to the South which they had offered to the North, by holding an examination at one of the three towns, Winchester, Southampton or Salisbury.* As the ignorance which still prevails, bjth among clergy and laity of the various ways in which assistance is given by the Committee of Council in support of scho ,1s is still great, notwithstanding the information contained in the Blue Books, the following brief statement of the principal of them may be useful to many into whose hands this book may fall, although, to give this information does not always encourage others in the way one expects it to do. I men- tioned them to a wealthy farmer not long ago, and also a large grant made towards building a school in a neighbour- ing parish, thinking it would encourage him to promote one in his own ; but instead of this, to my surprise, it had a contrary effect, and he wondered " how Government could venture to spend public money in that way." The assistance from, the Committee of Council is not only in building, which is given under certain conditions, to the extent of one-half the cost of building schools and teachers' houses ; but what is of still greater importance, assistance in the following ways is given for making the schools effective when bu. ; lt : 1. Augmentation of salaries to certified masters and mistresses, varying in amount according to the class of certificate, from 15 to 30 per annum for masters and from 10 to 25 per annu 11 for mistresses. * T.iesii examinations have now assumed a very important cha- racter, and are held annually in the spring <>:' ihu year in n.ore lima sixty different places in England. Any i,i formation relating to them may be had by application to tae secretary of the Society of Arts (1860). VI PREFACE. 2. Stipends to public teachers, beginning with 10 for the first year, and increasing 2 10s. each year to 20 in the last, and at the end of their apprenticeship they have an opportunity of going to a Training School as a Queen's Scholar, for one or two years, free of expense or nearly so. 3. Gratuities to masters and mistresses for instructing their pupil teachers during apprenticeship, 5 per annum for the first, 4 for the second, and 3 for every additional apprentice. 4. Capitation grants of 6s. per head in boys' schools, and 5s. for girls, for all children who have attended 176 days in the year, and are paying at least one penny per week to the school, and not more than 4d. per week : an annual attendance of eighty-eight instead of 176 whole days in school in the rural districts, will be accey.ted for boys over ten years of age, provided a scheme shall have been ap- proved, to provide for the alternation of lessons in school with ordinary labour. 5. Assistance in the purchase of school books, and of all useful educational apparatus, which are to be had at reduced prices, and which may be applied for once a year ; and the advantage of being made acquainted with what is best in this way,* no small advantage, particularly in a rural district. 2. Annual inspection and published results of it, which are necessary to any school system expecting to be efficient. * A revised list of apparatus for scientific instruction, in a Special Report, by the Rev. F. Temple, has just been issued by the Council of Education, to which is added, in an appendix, a list of maps, diagrams, models, etc., approved of by the Department of Science, :md Art, with the prices. It gives all the information on this head which, can possibly be wanted. The Committee of Council will grant to schools, in which pupil- teachers are apprenticed, pecuniary assistance to the extent of two- thirds of the cost, and of suitable cabinets to instruct them. Ap- paratus may be selected to the amount of 10, 15, or 20. The master must be examined in order to give proof of his qualification to use the apparatus selected lor any school. The text-books of examination are named under each of the divisions of the list, and the term of examination is the same as for certificates or for registration. In the case of masters already holding certificates of merit, spe- cial examination is waived, if the selection be made from the revision of mechanical and geometrical parts of the list, or from some of the more elementary parts of the physical science list. KtEFACE. Vll These things may be known to certified teachers ; but it is desirable they should be able to point them out in a brief form to those among whom they live. A very important change has lately been made by the Committee of Council in the conditions of being eligible to Queen's Scholarships in the Training Schools. Hitherto it has been limited to those who had been pupil-teachers ; but the examination is now thrown open to others ; young persons of both sexes, who may be well qualified by ac- quirements and disposition, are now eligible. To use the words of Mr. Lingen's letter to Her Majesty's Inspector of Schools : " Their Lordships have thrown open the examination for Queen's Scholarships to a new class of competitors, and they anticipate that a considerable supply of candidates may be found among young persons who are now assist* ants in private schools among untrained schoolmasters and schoolmistresses desirous of improving their attain- ments among Sunday-school teachers and generally among all those individuals with a natural aptitude for the work of instruction, who become known, from time to time, to the clergy and other promoters of education ; and who, with a little preparatory assistance in their private studies, may readily be made to reach the standard of examination.'' There is a prevailing opinion, that in the examination of teachers for a certificate of merit, by the Committee of Council, a knowledge of subjects far beyond those of an elementary kind is expected ; and that, in consequence of this, many deserving and well-qualified schoolmasters and schoolmistresses will not venture into the examination. Now, this impression about the difficulty of the exami- nation, I believe to be quite an erroneous one, judging from my own experience and knowledge of many school- teachers who have had the courage to go up for cer- tificates of merit, and have succeeded; and Mr. Lingen, the secretary to the Committee of Council, writing in 18) or a -whole. In the same way with measures of space, thus leading them by gentle degrees to see that in numerical fractions what is called the denominator denotes the number of equal parts into which a whole is divided, and the numerator the number of parts taken. "When sufficiently advanced to commence the arithmetic of Fractions, the teacher will find it of great service in giving them correct ideas of the nature of a fraction, to call their attention as much as possible to visible things, so that the eye may help the mind to the divisions on the face of a clock or of the degree or degrees of latitude on the side of a map, thus J L showing 5 TV, -ft, A (* *), T\, T"I T\, iS, iii *!> or units > showing how these may be reduced to lower terms, and that the results still retain the same absolute value that the value of a fraction depends upon the relative, and not upon the absolute value of the numerator and denominator; as T \ and , ^ aQ d J, T * r and $, -ft and , etc., have in each case the same absolute value. In casting his eye round a well-furnished school-room, the teacher will see numberless ways in which he may make 54 . SUGGESTIVE HINTS. the nature of a fraction clear to them, as counting the number of courses of bricks in the wall say it is fifty, as they are of uniform thickness, each will be -5? of the whole height placing the two-foot rule against the wall and seeing how many courses go to making one foot, two feet, etc., there will be such and such fractions or sup- posing the floor laid with boards of uniform length and width, each will be such and such a fraction of the whole surface, taking care to point out that when the fractional parts are not 'equal among themselves they cannot put them together until they are reduced to a common denomi- nator, and the reason of all this. In this way, and by continually calling their attention to fragments of things about them and putting these together, children get a cor- rect idea of numerical fractions at a much earlier age than is generally imagined. The following kind of question interests them more than very abstract fractions ; the teacher should try to form questions connected with their reading. What are the proportions of land and water on the globe ? $ land, I water. What do you mean by ? A whole divided into three equal parts, and two of them taken. Here the teacher would put a piece of paper into a boy's hand, and tell him to tear it into three equal parts, and show the fractions; or by dividing a figure on the black board. What proportion of the land on the globe does America contain? i. What Asia? i. Africa? i. Europe? &. And Oceanica? T V Now, putting all these fractions together, what ought they to give ? The whole land. The unit of which they are the fractional parts was what ? The land on the globe. Work this out. Africa, i or T \ ; Europe and Oceanica, each being &, these with Africa will be -fs, or -}. America and Asia together are f , and adding i to this gives 3, or 1 for the whole. Having been taught this and decimal arithmetic, they should be taught to work out most of their sums decimally, and made to reason about them as much as possible, rather than to follow a common rule for instance : What is the interest of 500 at 5 per cent, for two years ? ARITHMETIC. 55 5 per cent, means -what? the interest on a hundred pounds for a year: then the interest of 1 will only be the one hundredth part of that : work it out, -05 the interest of 2 will be twice as great; of 3 three times as great; and of 6 six times as great, etc. Having the interest for one year, the interest for any number of years will be the interest of one multiplied by that number, etc.* Children sometimes get into the way of working out questions of this kind, without having any definite idea of what is meant by so much per cent, etc. ; this they should be made thoroughly to understand, as bearing upon many other questions besides those on interest, as will be seen * The following algebraic formula may be useful : Let P = the principal. r = the interest of 1 for one year. n = the number of years, or the time for which it is put out. Now if r is the interest of 1 for one year, it is clear the interest of 2, 3, 4, etc., P will be twice as much, etc. or 2r, 3r, 4r . . . . Pr interest for one year. The interest for 2, 3, 4 .... n years will be 2 Pr, 3 Pr, 4 Pr, . . . . n?r. (1) the interest = rP, we have the amount, being the principal added to the interest, M = P+wrP. Now, in this equation there are four quantities, any three of which being given the fourth can be found. Ex. Interest on 250, for 2| years at five per cent. Here P = 250 5 > = = -05. 100 n = 2 = 2-5. /. I = 250 X (05) X (2-5) = 31-25, andM = 250 + 31-25 = 281-25. But the ab >ve formula is mucQ more important than the ordinary rule, inasmuch as it accommodates itself to every possible kind of case. A certain sum put out to interest at 5 per cent,, in four years amounts to 250 10s.; what was the sum put out ? In this case, M, r, and n are given to find P. Or the sum put out was 30, and in two years amounted to 33; what was the rate per cent. ? Here M, P, and n are given to find r. The cases where all, rate per cent., time, etc., are fractional, are quite as easy as the rest, except in having a few more figure* to work out. 56 8T7GGESTIYE HINTS. from the examples given ; also what is meant by so much in the shilling, so much in the pound, etc., that if a per- son spends twopence in the shilling in a particular way, and lays out two, three, ten shillings, he spends 4f planks required . . . . 6o2 4. The pfime Ftone placed on a platform of wood, and dragged over a flour of plunks required 608 5. After soaping the two surfaces of wood, which slid over each other it rt quired 182 6. The same s'one WHS no\v planed upon rollcis of three inches diameter, when it. required to put it in motion along the floor of the quarry 34 7. To drag it by these rollers over a wooden floor .... 28 8. When the stone was mounted on a wooden platform, and the same rollers placed between that and a plunk floor it required 22 From this experiment it results, that the force necessary to move a stone along Tart of Us weight. The rotigri chiselled floor of its quarry is nearly . . ^ Along a wooden floor $ By wood upon wood If the wooden surfaces are soaped -fc With rollers on the floor of the quarry *fa On rollers on wr od T ' 5 On rollers between wood ^ Prom a simple inspection of these figures it will appear how much human labour is diminished at each succeeding step, and how much is due to the man who thought of the grease. MECHANICS. 83 Care should be taken in introductory books containing fonnuUe to work from, the proofs of which the teacher per- haps does not understand, that the expressions are correct. 1 am led to make this observation from the following cir- cumstance : when I first introduced this working from formulae in the school here, I happened to go in one day when the boys were working out practical results between the power and weight of an inclined plane ; this they were doing by taking the power to the weight, as the height of the plane to the length of the base, in the case of the power acting parallel to the plane ; I was at a loss to conceive why master, boys, etc., should look so confident, even after I had pointed out to them the absurdity it led to in a particular case, instancing that if P : "W : : H : length of the base, H and P = "W , when the base became nothing length of base and the plane vertical, the power, instead of being equal to H the weight, became infinite, the expression becoming "W ; but taking it as the length of the plane, when the plane was vertical, L and H were equal, and the expression H H P = W W0 uld become P + W - "W, length of plane H as it ought to be. This I found arose from their having been reading a lesson on the inclined plane ; and the error was, in the for;iiula given in the note to the lesson ; the confidence of ths boys in the authority of the book, made it rather amusing to observe the shyness with which at first they received my explanation. The great art in teaching children is not in talking only, but in practically illustrating what is taught ; for instance, in speaking of the centre of gravity of a body, and merely saying it was that point at which, if supported, the body itstlf would be supported, might scarcely be intelligible to them ; but showing them that a regular figure, like one of their slates, would balance itself on a line running down 84 SUGGESTIVE HINTS. the middle, the lengthway of the slate, and then again on another through the middle of that, and at right angles to it, they see, as the centre of gravity is in both lines, it must he where they cross ; and, accordingly, if this line he supported, the body will be at rest this they understand. Again, balance a triangle of uniform density on a line drawn from one of its angles to the middle of the opposite side the centre of gravity will be on that line balance it again on a line drawn in the same way from one of the other angles the centre of gravity of the body will be in the intersection of these two lines. In the same way methods of finding the centre of gravity of other regular figures mechanically might be pointed out. The teacher should also make himself acquainted with the theory of bodies falling by the force of gravity that it acts separately and equally on every particle of matter without regard to the nature of the body that .all bodies of whatever kind, or whatever be their masses, must move through equal spaces in the same time. This, no doubt, is contrary to common experience bodies, such as feathers, etc., and what are called light substances, not falling so rapidly as heavy masses smoke, vapour, balloons, etc., ascending ; all this to be accounted for from the resistance of the atmosphere. The spaces described by a falling body being as the squares of the times that if it describe 16r\ feet in one second, in 2, 3, 4, etc., seconds it will describe 4, 9, 16, etc., multiplied into 16-rV. To show that while the spaces described in one, two, three, etc. seconds are as the numbers 1, 4, 9, 16, etc., those actually described in the second, third, fourth, etc., successive seconds are as the odd numbers, 3, 5, 7, 9, etc., showing very strikingly the accelerated motion of a falling body. To apply this also to the ascent of bodies projected directly upwards, with a given velocity. Again, the moving force of bodies being equal to the mass multiplied into the velocity: How a small body, moving with a great velocity, may produce the same effect MECHANIC'S. 85 as a large body with a small one as a small shot killing a bird a large weight crushing it to death. Interesting observations of a simple kind might be made on the strength of timber weights suspended on beams between supports, such as the walls of a building these coming under the principle of the lever, etc.; also such simple things as the following might be asked : Why is it easier to break a two-foot rule flatwise than edgewise ? and why joists are now always made thin and laid edgewise ? which our forefathers did not understand. Although the reasons are sufliciently simple, very few even amongst the tolerably well educated c. give a satisfactory explanation of them. The usual answer, that " it breaks more easily because it is thinner" will not do. Wood, and all fibrous matter, is much stronger in the direction of the fibre than across it,- and the strength varies as the square of the dimensions in direction of the pressure, multiplied into the dimensions transverse to it, when the , breadth x depth 2 length is given, or generally as the j IT - - It is a curious fact, but completely proved by experi- ment, that hollow tubes are stronger than solid ones of the same quantity of material how beautiful this provision of Nature, as shown in the structure of the bones of animals, more particularly in those of birds' and the larger quadru- peds, giving them the greatest strength, and encumbering them with the least possible weight. , As a means of testing with accuracy and of forming some definite idea of the strength of the hollow stems of plants, etc., the following simple experiment, which I wit- nessed, by the late Professor Cowper, of King's College, London, is very instructive : He placed a length of one inch of wheat straw in a ver- tical position in a hole bored in the lower of two parallel boards, held together by a hinge of the same height, one inch, and then brought down the upper part upon it. This he loaded with .a load of sixteen pounds, without any appearance of breaking, and stated that he had known a straw bear as much as 35 Ibs. placed in this position before it broke. 86 SUGGESTIVE HINTS. NATURAL PHILOSOPHY. Nature herself seems to give a very instructive hint on this part of education, in the amusements of early childhood. "We see a child as soon, as it can use its hands, trying to move, or to lift anything which it can, placing it first in one position, then in another, and trying it in all the various ways which its senses admit of in fact, making a variety of experiments with it, and this is generally looked upon as a mere amusement : but children when thus employed, arc, as has been observed by Dr. Rci* " acquiring the habits of observation, and by merely indulging an undetermined curiosity, are making themselves acquainted with surround- ing objects. If some new effect occurs from any of their little plays, they are eager to repeat it. When a child has for the first time thrown down a spoon from the table, and is pleased with the jingling noise upon the floor, if another or the same is again given to him, he is sure to throw it down, expecting the same noise to occur ; but if a piece of wood is given, he very soon finds out that the same effect does not take place, and is no longer anxious to repeat the experiment. So long as the noise goes on, the child has pleasure in repeating it, and if two objects are given, one of which produces a noise when thrown down in this way, and the other not, he very soon finds out the difference, and acts accordingly, and this is, in fact, the method of induction. The child is thoroughly persuaded that a jing- ling noise is sure to follow his throwing down the spoon, and goes on repeating it till he is tired." " Such," observes the same philosopher, "is the educa- tion of kind Nature, who, from the beginning to the end of our lives, makes the play of her scholars their most instruc- tive lessons, and has implanted in our mind the curiosity and the inductive propensity by which we are enabled and disposed to learn them." It is an observation of the late Professor Daniel, in some of his works, " that the principles of natural philosophy are the principles of common-sense," and from my own experience here in introducing this kind of teaching into XATUBAL PHILOSOPHY. 87 the school, I am confident that, with those who have been able to remain to an age to profit from it, it has given an interest in what they are learning, and a kind of practical character to it, which no other teaching could give. I recollect many years ago, going into a school in Ger- many, and a German gentleman with whom I was, observed of something they were teaching, " das ist kein practicables ding," that is no practicable thing the impression made at the time has remained on my mind ever since. We look upon the Germans as a people fond of theories, but this appeared to me a sensible remark. The following hints are intended to show to our school- masters, of the class for which this book is intended, the importance of being so far instructed in subjects of this nature as to be able to point out, in a common-sense way, some of those results in science which bear more imme- diately on the occupations of life ; these will be found not only interesting and instructive to the children while at school, but may be most useful to them after they have left it. As a class, ao doubt, at the present day, the far greater number of our schoolmasters are not qualified to give this instruction, but there are many, and that number, I hope, increasing, who are; to such, although the following pages may not add much to their knowledge, they may perhaps suggest something in the way of imparting it, and in bring- ing it to bear upon their teaching. They will also point out to others some things with which they may easily make themselves acquainted, and a few simple experiments which are easily tried. Among the more striking of these things will be such as the following : the elastic and other properties of air the nature of aeriform fluids of water how the pressure of fluid bodies differs from that of solids how these proper- ties enable man to turn them to useful purposes, such as windmills, watermills, etc. Civilized man is able to take advantage of these proper- tis, and avail himself of them as motive powers in the business of life ; the savage, on the contrary, observes the trees torn up by the Avinds, stones and rubbish carried down 88 SVGGESTIYE HINTS. by mountain torrents, but is unable to turn this observation to any useful purpose. Archbishop AVhately, in his " Introductory Lectures on Political Economy," observes: "Many of the commonest arts, which are the most universal among mankind, and which appear the simplest, and require but a very humble degree of intelligence for their exercise, are yet such that we must suppose various accidents to have occurred, and to have been noted many observations to have been made and combined and many experiments to have been tried in order to their being originally invented. " And the difficulty must have been much greater, before the invention and the familiar use of writing had enabled each generation to record for the use of the next, not only its discoveries, but its observations and incomplete experi- ments. It has often occurred to me that the longevity of the antediluvians may have been a special provision to meet this difficulty in those early ages which most needed such help. Even now that writing is in use, a single individual, if he live long enough to follow up a train of experiments, has a great advantage in respect of discoveries over a suc- cession of individuals ; because he will recollect, when the occasion arises, many of his former observations, and of the ideas that had occurred to his mind, which, at the time, he had not thought worth recording. But previous to the use of writing, the advantage of being able to combine in one's own person the experience of several centuries, must have been of immense importance; and it was an advantage which the circumstances of the case seemed to require." And first, of the atmosphere a sphere of air surround- ing the earth has substance and weight, but is invisible elastic, can be squeezed into a less space by pressure ex- pands again when the pressure is removed expands by heat and contracts by cold. This may easily be made in- telligible to them in the following way : Take a tumbler and invert it or better, take a jar used for gases, with an air-tight stopper, and placing its mouth horizontally on the surface of the water, in a pneumatic trough, or in any vessel of sufficient depth, having a shelf for support, show them, by letting them feel it, the difficulty XATUKAL PHILOSOPHr. 89 of pressing the jar down it offers resistance increase the pressure, the air occupies less and less space, hut the water inside the glass does not rise so high as on the outside ; difference owing to what ? point out. Diminish the pres- sure, it again expands, showing its elasticity. Of course the attention of the children must be called to the surface of the water inside and outside the jar. Take out the stopper, the jar sinks hy its own weight, proving clearly that the resistance was offered hy the air. Again, allow the jar to fill with water, put in the stop- per, and raise the jar nearly to the surface of the water in the trough explain why the column of water is supported, and would he supported if the jar were 33 feet high at the ordi- nary pressure of the atmosphere take out the stopper, the water immediately falls ; or while the column of water re- mains show how the jar may be filled with air, by carrying down successive tumblers of it until the jar is filled. From this, the method first used of taking down barrels of air into a diving-bell is easily understood. "Why is it necessary to have a vent-peg in a barrel ? or how does it happen that the tea-pot sometimes will not pour? etc. Air expands by heat. Experiment : a half-blown bladder placed before the fire, the wrinkles disappear, the air ex- panding it ; remove it, the air again contracts. Place the same under the receiver of an air-pump, it ex- pands from diminished external pressure. Air has weight. A bottle exhausted of the air is lighter than when full difference, the weight of a volume of air equal to the contents of the bottle this means air at the ordinary temperature and pressure of the atmosphere 100 cubic inches dry pure air weight 31-0117 grains, being for a cubic yard 4| oz. Balance the bottle when full of air at one end of the scale-beam ; then take it off and exhaust it by means of the air-pump, and when again suspended, the other end of the beam will preponderate ; restore the equilibrium by pieces of paper, etc. Drinking through a straw. The teacher, taking a straw and a basin of water, shows them, if the mouth or orifice of the straw is not wholly immersed, or under water, the water will not rise : wholly covered when they begin to 90 SUGGESTIVE HINTS. draw out the air the water immediately rises, and why ? What takes place if a hole is made in it above the surface of the water ? Water does not rise. What if you plunge it deeper, so that the hole made in the straw is below the surface ? It immediately rises again. Reasons for all this, which, if they comprehend, they will at once understand the barometer and common pump. A model in glass of a common pump will be found a very instructive piece of apparatus, and if fitted into a small glass cylinder which can be made air-tight at pleasure by means of a screw, it becomes a much more useful and perfect instrument for teachers, as the pump will work or not, according as the vessel in which the water is, is made air-tight, or not air-tight. Again, a piece of wet leather with a string attached, called a sucker ; press it with the foot against a stone remove the air between the leather and the stone, leather, say a square piece three inches on a side, ought to support 9X15 pounds, only supports, say 80 Ibs. reason whyr The vacuum not complete. Then take a circular piece, three inches diameter, let them find the area, and calculate how much it ought to support. This is the principle on which a fly is able to walk along a pane of glass, or across the ceiling. The common syringe. The pop-gun they are in the habit of making out of apiece of the elder-tree how, by pressing down the rod, the elasticity of the air forces out the pellet at the other end : when they cease to press the rod of it down, the elasticity of the air within forces it back. A pair of common bellows. Show them the construction the valve, or trap-door in the bottom board, opening only inwards the bellows fill with air when the boards are separated valve shuts down, and the air goes out at the nozzle when they are pressed together will not work when turned upside down, why? the current of air makes the fire burn better ; the reasons for all this. The teacher should have a pair of bellows, and show what takes place at each movement of the board, and let them handle them themselves. The barometer. The teacher shows them the instrument, how constructed, and what it is for ; pressure of the air supports a column of mercury about 30 inches, a column NATURAL PHILOSOPHY. 91 of water about 33 feet the height of the column being less in proportion as the specific gravity of the fluid is greater not so high if carried to the top of a mountain, and why ? the temperature at which water boils varies with the height of the barometer boils at a less heat on the top of a mountain than at the bottom. The mode of ascertain- ing the height of mountains by means of the barometer. Why this method is more to be relied on in tropical climates than in high latitudes, etc. Pascal, in France, about the year 1647, was the first to make this experiment, which he did at the summit and foot of a mountain in Auvcrgne, called Le Puy-de-D6mc, the result of which led him to conclude that the air had weight. He also tried it at the top of several high towers, which convinced him. of the weight of the atmo- sphere. To register the daily altitudes of the barometer, and the thermometer, would be a very useful exercise for the pupil-teacher and in its bearings branches out into a great many things. The principle of the common pump might now be ex- plained how the atmospheric pressure which supports the mercury enables them to pump up water having a model of a pump, or even with paper and pasteboard, showing the kind of tubes and nature of the valves, this may be clearly explained pointing out how the valves act at each separate movement up and down of piston-rod the limit to which water can be raised the experiment of Torricelli, etc. Supposing the atmospheric pressure about 15 Ibs. on the square inch how much on five square inches ? -how -much on five inches square ? on a square three inches on a side? on the surface of the floor or the table ? making them have recourse to the two-foot rule ; pressure on the animal body, etc., and how counteracted. A fish under water has the pressure of the air, 1 5 Ibs. on the square inch, besides the pressure from its depth in the water ; a basin of water with a live fish in it, when placed under the receiver of the air-pump and exhausted, the air-bladder expands, and the fish turns on its back. 92 SUGGESTIVE HINTS. Children may easily be made to understand that the atmosphere is an aeriform fluid surrounding the globe, acted on like other bodies by the force of gravity, consisting prin- cipally of two airs or gases, varying in weight, and partly of a third, heavier than either of the others, but if placed upon each other in the order of their specific gravities, the heaviest nearest the surface of the earth, next heaviest in the middle, and the lightest at the top, that they would not remain in this order of superposition, as, for instance, the three fluids, quicksilver, water, and oil, would do ; but the heavy one at the bottom would rise up and travel through the pores of the other, and the lighter one would descend, this being a property peculiar to bodies of this nature, and called the diffusion of gases. That, in addition to this, there is an atmosphere of vapour of water, arising from evaporation from the surface of the earth and of water, and which is in itself lighter than dry atmospheric air ; a cubic inch of water at the common atmospheric pressure forming about 1 700 cubic inches of vapour : therefore a cubic inch of vapour of water is about -rrW of the weight of a cubic inch of water a cubic inch of common atmo- spheric air about -g&v. Having called their attention to the fact that a substance lighter than water will, if plunged into it, rise to the top ; that of two fluids the lighter will rest upon the heavier ; arranging themselves according to their specific gravities as water upon mercury oil upon water cream upon milk they will easily understand why bodies lighter than air ascend in it, as the smoke from their chimneys tell them to watch it, particularly on a still, calm day why it stands still and does not rise higher ; the principle on which a balloon ascends, a soap-bubble, etc. Again, why there is a draught up the chimney ; the air rarefied, how this takes place ; why a current of air under the door and towards the fire and another perhaps out of the room at the top of the door ? The kind of resistance offered by the air to a falling body this increases with the density that, under the re- ceiver of an air-pump, a guinea and a feather would fall at the same time. XATTJRA.L PHILOSOPHY. 93 As a simple experiment, showing the effect of rarefac- tion of air, the teacher might light a piece of paper, and while burning, place it in a tea-cup, and invert the cup in a saucer of water the water will immediately be driven into the cup with a gurgling noise. Again, in the practice which cooks' have of putting an inverted tea-cup in a fruit pie, as they think with a view to prevent the syrup running over as the pie bakes, the air in the cup becomes rarefied, and is driven into the pie-dish, through the crust, into the atmosphere when taken out of the oven it cools, the rarefied air in the cup is condensed, but as the mouth of the cup is surrounded with the juices of the pie, air cannot get into it, but it forces the liquid up. The teacher explains why the resistance of the air in moving along is so little felt some of the consequences of its being disturbed, and causes its being put in motion a breeze, a hurricane, etc. ; he would also speak of the forces of these at different velocities the force varying as the square of the velocity. This short table might be the subject of a lesson : Velocity of the wind in miles per hour. Perpendicular force on one square foot in pounds. 5 10 20 40 80 123 492 1-968 7-872 31-488 Gentle wind. Brisk gale. Very brisk. High wind. Hurricane. It will be easy to calculate the force of the wind acting on a given surface, doing so in particular cases will be in- structive. Air as a vehicle of sound. A bell under the receiver of an air-pump when ex- hausted, is not heard. Bodies which produce the sensation of sound on the ear are in a state of vibration, as in a bell the running a wet finger along the rim of a common drinking-glass, etc. Here having to do with the instruction of children en- 94 SUGGESTIVE HINTS. gaged in country occupations, I hare called their attention in this, as in other subjects, to things coining under their observation, in a way something like the following : Did you ever observe a woodman cutting down a tree at a distance ? you could see the hatchet fall, and some time after that the. sound of the blow came to your ear. Do you know the reason ? Teacher. Light travels so fast that the time it is in coming from the hatchet to you is so small that it cannot be reckoned ; so that when you see the hatchet fall, that is the instant the blow is given ; but sound, coming at a very slow pace (1142 feet in a second), takes as many se- conds to get to your ear as when multiplied by 1 142, would give the number of feet between you and the man cutting down the tree. For instance, if it were 2", his distance would be 1142ft. x 2 ; if 3", 1142 x 3, and so on. Did you ever see a man firing a gun at a distance, and after seeing the flash, wonder why you did not hear the sound, or that you were kept considering how long it would be before the sound came ? Do you know the reason can you explain it ? Because sound lags behind, and the flash takes up no time in coming to the eye. Supposing you were 5" before you heard the sound after seeing the flash, how far would you be off? 5 x 1142 ; 6", how far?- 6 X 1142, and so on. When we hear the Portsmouth guns here, if you could have seen the flash, do you think you could find out the distance betwixt this and Portsmouth ? Supposing a man was standing where you could see him a mile off, and you saw the flash of his gun, how long would it be before you heard the sound ? A mile in feet divided by 1142 would give the number of seconds before I could hear the sound. Teacher. How do you think the sound gets to your ear ? The air in the gunpowder suddenly expands and dis- turbs the air immediately about it, or the hatchet causes a vibration or tremulous motion in the wood, which sets the air in motion all round about ; and this makes a sort of cir- cular wave, beginning from a point which gradually en- MTU UAL PHILOSOPHY. 05 largos, one circle of the air of the atmosphere strikicg against another, until it reaches the ear, unless it meets with some hindrance in the way ; just as when you throw a stone into a smooth pond, a wave, beginning from the stone, spreads in every direction, until it reaches the bank. The air is as necessary to continue the sound up to your ear as the water is to make the wave come up to the bank. Sound goes much quicker in water nearly four times as quick as in air, and in solids from ten to twenty times quicker ; so that if you splash in the water at one end of a pond, the fish would hear you much sooner than a hoy standing at the opposite side would do. Now, in order that you may understand how well solids convey sounds, the next time you see a solid log of deal, or timber not very knotty and broken in the grain, at the carpenter's shop, set one of the boys to scz-atch at one end of it, and the rest of you go and listen at the other. Try the same on a block of stone, marble, etc. But perhaps this will amuse you more : when you see the kettle on the fire, and you cannot tell whether it boils or not. place one end of the poker on the lid, the other to your ear, and it will tell you. If you strike \vilh a ham- mer on. a solid wall at one end, and some of you go and fix your ears against the other, you will most likely hear the sound of the blow twice the first going along the wall you may call the wall-wave (coming more quickly'), the second, a little after, through the air, coming with the air- wave, we have talked of before. Try if you can hear two reports of the same knock by tapping with a hammer at the end of a log of wood one along the wood, the other along the air. You have heard of the wild natives of America when they think their enemies are near, they lie down on the ground, and, by applying their ears to it, they can judge of the distance, and hear sooner than through the air. Did you ever hear what is called an echo ? Supposing you were to clap your hands violently toge- ther, that creates a wave in the air which carries the sound along with it; now, if this wave happens to meet with a wall or a rock, or any obstacle in its way, it is checked and 96 SUGGESTIVE HINTS. beaten back, and so brings the sound with it a second time to your ear ; and again, after passing you, if it met with the same sort of obstacle on the other side, it would be sent back again, and so strike your ear in passing and repassing, losing a little every time until it entirely died away. This would be called an echo ; people living in a flat country have not so many opportunities of observing it as those who inhabit a craggy and mountainous one. Water a fluid at the common temperature of the at- mosphere. Have you ever seen it solid ? In winter in frost it is then ice. How high does the thermometer stand when water begins to freeze? 32. Look at the thermometer in the room, how high 'is it? 52. How many degrees above the freezing point ? Does it increase in volume when it becomes ice ? Water from the tempe- rature of about 39, expands as it grows colder, and at 32. when it becomes ice, expands so as to crack water-bottles, water-pipes ; a piece of ice floats in water, part of it being above the surface ; if it were of equal weight with the same volume of water, it would just sink so as to have no part above. You should never let water stand in leaden pipes, or in vessels likely to be broken by its freezing in severe frosts. This expansion of water in becoming ice, how serviceable to the farmer, in some soils, in pul- verizing and making them fit for vegetation good for gardens, etc. " That water contracts in reducing the temperature to about 40, and below that again expands, is easily shown, by taking two equal thermometers, the one filled with water and the other with spirit ; placing them in melting ice, the spirit one will gradually fall to the freezing point, but the other will fall to about 40, and then begin to rise. By Act of Parliament, the temperature at which the specific gravity of spirits is determined by the excise, and at which the standard weights and measures are adjusted, is 62 of Fahrenheit." Daniel's " Chemical Philosophy." Quicksilver, unlike water in this respect, contracts and becomes denser in becoming solid. It has been ascertained, by leaving it exposed to the cold in high latitudes, where it has assumed a solid form, and observing the temperature SAUJRAX PHILOSOPHY. 97 at which it begins to thaw, that the freezing-point is about 40" below zero of Fahrenheit. Attention may be called to the way in which the roads are raised up in winter by the freezing of the moisture within them how after a thaw a loaded cart or waggon sinks in, causing deep ruts how rocks and stone, which have absorbed much moisture, split after frost parts of buildings peel off, etc. Can water be made into a vapour something you cannot see? By heat it becomes steam, thermometer 212 at the average pressure of the atmosphere; one inch of water makes about a cubic foot, 1728 inches ; if further heated it exerts a greater pressure in trying to escape, pressing on the surface of the vessel in which it is. This is the property which makes it so serviceable to us in grinding our corn, moving the machinery for spinning and weaving, of steam-boats, etc., and as a motive power on. our railroads, carrying us forty or fifty miles in an hour. If cooled below 212 it immediately falls back, shrinks up into one inch, and becomes visible water again, giving out a great deal of heat; instance steam raising the kettle-lid. "Why does the tea-kettle, just before boiling, very often force out a quantity of water from the spout? Because the air, driven from the water by heat, and the steam which is forming from the water, rise to the top, and the lid happening to be air-tight, it cannot escape, and being lighter than water it cannot descend, ^o the vapour or steam under the lid increases and expands, and, pressing upon the surface of the water, forces it out at the pipe. Did you ever see on a frosty day, when you were going with a team, what you call the breath of the horses, or your own breath ? Yes, sir. Teacher. The warm air from the horses' mouths, or from your own mouth, containing vapour which you cannot see when the air has a certain degree of warmth in it, as soon as it comes in contact with the colder air gets cooled, and the steam or vapour becomes water (is what they call condensed), or perhaps watery vapour, which you can see, instead of a vapour which you could not see. 98 SUGGESTIVE HINTS. Did you ever see sugar or salt melted in water ? !N"o, sir ; but we have seen sugar in tea. Then the teacher takes a small phial containing water, and puts in a certain quantity of salt, when entirely melted they see the fluid perfectly clear; increase the quantity beyond what the water will take up, this remains un dissolved. If the tem- perature of the water were increased, it would take up more; in the same way the air will take up a greater quantity of vapour the warmer it is, and coming from the mouth warm, it holds more vapour than it is able to do when it comes in contact with the cold air, and throws some of it down, so that you can see it ; thus water on the inside of the window in frosty weather dew on the outer surface of a bottle of cold water in hot weather, etc. the quantity of watery vapour in the air in hot climates greater than in cold, hence torrents of rain when it is suddenly cooled, etc. About London, latitude 51 30', the average fall of rain in the year is about 23 inches ; while in Rome, latitude 41 54', it is 38 inches ; at Calcutta, latitude 22 34', it is 81 inches ; and in climates like the West Indies upwards of 100 inches ; but though the quantity of rain falling in hot countries is greater than in the temperate ones, the number of wet days is greater in the latter than in the former ; there is more moisture in the air in our climate in summer than in winter; but from the greater temperatm-e it is held up, and is not so sensible to us. By inches of rain is meant the depth at which it would stand on every square inch of surface on which it falls, supposing none to be absorbed by the soil or to evaporate. Two fluids in the same vessel, one lighter than the other, which would get to the bottom ? The heavier one. Give instances. Milk and cream, water and oil, quicksilver and water, water and air. The teacher, holding up a glass : What is this glass full of? Atmospheric air. If I pour in water, what does that do ? Drives out the air, because it is the heavier fluid. If I pour quicksilver into a glass of water, what would take place ? The quicksilver would drive out the water for the same reason. If water upon mercury, or oil upon NATUIUL PHILOSOPHY. 99 water ? The water or oil being the lighter fluids, would rest on the top, and the same thing would take place if carbonic acid or any gas heavier than air were poured in. Another instance : fill a small phial with water, leaving room for a bubble of air, then cork it ; holding it in a horizontal position the bubble rests in the middle, elevate one end, the bubble rises to the top ; show how this may be used as a spirit-level. Look at that cubical vessel on the table, divided into two equal parts by a division in the middle. Suppose one division full of mercury, the other of water, and the par- tition suddenly withdrawn, what happens ? The mercury immediately covers the bottom of both parts, and the water rises to the top. Take a bottle of water from a cool spring or from the pump ; place it in the sun or in a room for instance, as you see it sometimes in a bed-room. You will observe air- bubbles form themselves on the surface of the glass at the bottom and the sides this is air contained in the water. As it takes the temperature of the room, these air-bubbles form themselves, expand as they rise, come suddenly to the top, the water being of equal tem- perature throughout. Why does the bubble expand as it rises ? The pressure upon its surface varies as the depth ; and therefore the nearer the surface the less the pressure. How is it, then, if you place water in an open saucepan on the fire to heat, we see at first bubbles form themselves at the bottom, like pieces of glass, rise up a little way, and are then lost before coming to the surface. The air in that part of the water in contact with the bottom of the saucepan, immediately begins to feel addi- tional warmth, forms a bubble, rises up a little way, and although the pressure is diminished, it becomes again com- pressed, in consequence of coming in contact with cooler water as it rises. This it is, I believe, which causes what is called the hissing of the kettle. If you were to boil a quart of water until it has all, as you call it, boiled away, what has become of it ? All turned into steam. If water with chalk or salt in it ? 100 SUGGESTIVE HINTS. The water would go into vapour, and the chalk or salt be left behind at the bottom of the kettle. Did you ever see a white crust at the bottom of your tea-kettle ? Yes, sir ; but we don't know what it is. Don't you know we live upon what is called a chalk soil here, and the rain that falls makes its way through the chalk and comes out underneath it, having taken up some of the chalk in its way through. If our hills had been of iron ore, lead, or salt, the water would have taken up some of these substances in passing through them, as it always takes up some of the earth through which it niters as it is a fluid in which many things are soluble ; thus, we get water with chalk in it when you boil it, the pure water goes off in vapour, and leaves the chalk behind, which falls to the bottom of the kettle : besides this, although hot water will hold up or melt more sugar or salt than cold, yet it will not hold more chalk ; on the contrary, less, as the heating drives off a particular gas or air (called car- bonic acid gas), which has a great liking for the chalk, and holds it up in the water, so that what falls to the bottom partly belongs to the water which is driven off, and partly to that which is left in the kettle. These are two reasons, therefore, why your kettle has a white mass of chalk at the bottom. Taking off the lid of a kettle when the water is boiling, turning it up, what do you observe ? Drops of water. These are formed by the steam coming against the lid, cooling it down so that it becomes water the lid being in contact with the atmosphere conducts off the heat from the steam this is distilled water or pure water, containing no lime, salt, etc. Two fluids mixed together, which become vapours at different temperatures, may be easily separated thus a mixture of spirit and water ; heat the mixture up to the temperature at which spirit becomes vapour, it goes off and may be collected, the water remaining behind. That the boiling point of water or any other fluid varies with the atmospheric pressure how this may be applied to find the altitude of mountains that water at the top of Mont Blanc, for instance, boils at a temperature of about JfATTJEAL PHILOSOPHY. 101 137 that a difference of 1 in the boiling-point corre- sponds to about 530 feet of ascent, and this difference in boiling will denote a fall of about 0*589 inch of barometric pressure that, under the receiver of an air-pump, water may be made to boil at a very much lower temperature than in the air. This and other things of a similar kind I find, from experience, may be made most instructive and useful to them, and more particularly if a school is provided with philosophical apparatus with which the experiments can be shown. A table of the temperatures at which different fluids boil and freeze should be suspended on the wall. Heat water to boiling in a Florence flask, cork it well when boiling, and turn the flask upside down; having removed it from the lamp, it now ceases to boil ; sprinkle water on the surface of the bottle, the steam within is con- densed, and it again begins to boil ; when it again ceases to boil, from the elasticity of the steam within, repeat the sprinkling and it commences boiling again. Thus the ap- plication of cold makes the water boil. Archdeacon Wollaston invented an apparatus of such delicacy for ascertaining this, that the difference of the height of a common table from the ground would produce a difference in the boiling-point, which was clearly shown by the instrument. The different ways in which water and metals are heated hot current ascending, the cold water descending, and metals from particle to particle ; point out also the differ- ence in the process, in attempting to heat water by placing the fire above and not under the vessel containing it. The conducting power of fluids is very small, and it has been found that water may be made to boil in the upper part of a tube, without imparting much heat to the water below it, and that it maybe brought to the boiling-point within one fourth of an inch of ice, without the latter immediately melting ; and that ice is melted eighty times slower when it is fixed at the bottom of a cylindrical vessel with water above it, than when it floats upon the surface of warm water. Salt is got from sea- water by exposing it to the air in 102 SUGGESTIVE HINTS. large pans ; the water goes off in vapour and leaves the salt behind ; the greater the surface exposed to the air the more rapidly the water goes off. Shallow pans hetter than deep, and why ? Do you not observe the water lessen very much iu summer in your sheep-ponds, even when you do not take cattle to drink at them ? It is taken up by the air; in the same way a good brisk wind rapidly dries the hay, corn, and clothes after washing ; and if you want anything that has been washed to dry fast, you unfold it as much as you can in order to expose all its surface to the air. For the same reason you spread out the grass and leave the corn in the field, in .order that the fluid matter contained in them may be taken off. Salt also is found as a mineral in Cheshire, Poland, etc. ; and salt-springs are very often found in the coal-mines in some districts, particularly in Durham and Newcastle, where a great part of the salt used by the miners for their own domestic purposes is supplied by the salt-springs in the mines. The following is an easy instructive experiment : ^Take a small quantity of rock-salt and also of saltpetre, the crystals of which differ very much, dissolve them together in water, they form a clear limpid fluid. Pour this solu- tion of the two into a small dish, and let it evaporate ; crystals of pure salt and saltpetre will be the result, the beautiful long crystals of saltpetre being totally devoid of salt. This shows clearly that the atoms of salt have an attraction for and seek for their own atoms ; the same of the saltpetre ; and that If there is any attraction of the one for the other, it is less than that among themselves. Dew. When it is once understood that the air of the atmosphere holds up a considerable quantity of vapour, and that the greater its temperature the greater is the quantity which it holds, it will be easily understood that, when any portion of air comes in contact with a body colder than it- self, that it will throw down some of its moisture. During the daytime the earth, plants, etc., absorb heat from the sun ; when he goes down, they radiate or give off part of the heat they have absorbed, and consequently cool. This cools the air in contact with them ; and when XATDKAL PHILOSOPHY. 103 cooled below the point which enables it to hold up all the vapour which it had taken up during the day, it lets it fall again. This is called the dew-point. 2fow, some plants and some leaves and earths give off heat faster than others ; on" such a more copious dew will be deposited. On the con- trary, gravelled walks, stone, etc., give off heat less ra- pidly, and on them little or no dew falls. This all know from experience, or at least may easily ascertain it : then to call their attention to the beautiful drops of dew formed on the leaves the service they are to the plants the beautiful provision of the Almighty in causing the dew to fall more copiously on the vegetable world, which wants it, than on the mineral ; attraction of cohesion keeping the globules together, etc. "Why they disappear in the morning, again becoming vapour. Little or no dew on cloudy nights : why ? An umbrella overhead in an evening prevents the falling of dew on the person, on the clothes : the philosophy of this the clouds are an umbrella, and the reason why no dew falls on a cloudy night applies to the umbrella held over the head. Any schoolmaster taking an interest in this subject will see some very simple but curious and instructive experi- ments in Griffiths's " Chemistry of the Four Seasons." They consist in taking equal portions of dry wool, of a given weight, and placing them in the evening one on gravel, another on glass, another on grass, but sheltered by a slight covering a little elevated above it, and then at sun- rise taking them up and weighing them. Of course the increased weight, which will in all these positions vary very much, is the weight of water deposited in the shape of dew. These, and a variety of phenomena connected with this subject easy of explanation such as the mists, the fogs rising in damp, marshy places, following the course of a river, and many appearances of a like kind, which those living in the country are in the habit of witnessing, may be studied with great interest; but as it is merely my object to throw out what I conceive to be useful hints, I will not pursue it further. The force with which the absorption of moisture by porous bodies causes them to expand, is much greater 104 SUGGESTIVE HINTS. than those who have never thought on the subject have an idea of. As an instance of this, and of turning it to practical purpose, Sir John Herschel, in his " Discourse on the Study of Natural Philosophy," gives the following very interesting one, as a process which is had recourse to in some parts of France, where millstones are made : " "When a mass of stone sufficiently large is found, it is cut into a cylinder several feet high, and the question then arises how to sub- divide this into horizontal pieces, so as to make as many millstones. For this purpose horizontal indentations or grooves arc chiselled out quite round the cylinder, at dis- tances corresponding to the thickness intended to be given to the millstone, into which wedges of dried wood are driven. These are then wetted or exposed to the night dew, and next morning the different pieces are found separated from each other by the expansion of the wood arising from its absorption of moisture." This is a very curious instance of a simple natural power doing what would require great trouble and expense to effect, either by chiselling through, or by any machinery of sawing, sometimes used for dividing blocks of stone. The same author also mentions another instance where a knowledge of the laws of nature, although acting here in a different way, is called into action. In this case the heat first expanding, and then the application of the water causing a sudden contraction. In the granite quarries near Seringapatam the most enormous blocks are separated from the solid rock by the following neat and simple pro- cess : The workmen having found a portion of the rock sufficiently extensive, and situated near the edge of the part already quarried, lay bare the upper surface, and mark on it a line in the direction of the intended separation, along which a groove is cut with a chisel, about a couple of inches in depth. Above this groove a narrow line of fire is then kindled and maintained till the rock below is thoroughly heated ; immediately on which a line of men and women, each provided with a potful of cold water, suddenly sweep off the ashes, and pour the water into the heated groove, when the rock at once splits with a clean NATURAL PHILOSOPHY. 105 fracture. Square blocks of six feet in the side, and up- wards of eighty feet in length, are sometimes detached by this method. The following practical way of giving an insight into the principle on which bodies float in fluids lighter than them- selves, and of estimating their weight by the quantity of fluid displaced, has been found very serviceable : They* have two tin vessels, a larger and a smaller one, the large one having a small spout level with the top, so that, when filled with water and running over, it may dis- charge itself into the small vessel placed by the side of it ; the small one of known dimensions, say nine inches square at the bottom and six inches high, with a graduated line on one of the sides, so that it may be immediately seen to what height the water rises when flowing into it, and of course knowing the area of the base, and multiplying this into the height at which the water stands, will give its volume. Then they are provided with a number of cubes of wood, the woods of the parish, oak, elm, ash, etc., four inches on a side together with other pieces of any irregular shapes, for the purpose of experiment. Having filled the larger vessel with water up to the spout, and placed the smaller one under it, the teacher takes a cube of oak, for instance, floats it on the water, which immediately begins to flow into the smaller vessel, and when it has ceased to do so, the height at which it stands is observed. They then calculate the number of cubic inches of water displaced. This they know is equal to the number of cubic inches of oak under water (the teacher should show them the proof of this) that it is equal in weight to the piece of oak. Proof then knowing that the weight of a cubic foot of water, temperature about 62, is 1000 ozs., and why it is necessary to specify the temperature they cal- culate, for instance, the weight of a cubic inch, by dividing 1000 by 1728, the number of inches in a foot. Then multiplying the weight of one inch by the number of inches, this gives the weight of water displaced, and the weight of the wood. * This is speaking of the boys in King's Somborne school. 106 SUGGESTIVE HINTS. They then take the piece of wood, tie a string round it, weigh it by a spring-balance, and find this exactly agrees with the figures they have worked out; and it is this weighing which gives such a character of certainty to what they have been doing, which makes them take pleasure in the work. Weighing before floating it is better. Again, knowing the measurement of the piece of wood, supposing it to be one of known dimensions, subtracting the number of solid inches under water from the whole, gives them that part of the body above the surface, and which is floating in air. The same would be done with pieces of ash, elm, fir, etc. Also in winter, pieces of ice aiford a teacher who under- stands the subject an opportunity of giving a useful lesson pointing out how water becomes solid at a particular temperature that although water freezes at this particular point, yet pieces of ice may have a temperature far below this that a piece of ice, temperature 20, as measured by Fahrenheit, would be of more service for cooling butter, water, etc., than one at 32, and so on. The teacher might ask such a question, What is the atmospheric pressure on the surface of the water in the vessel? making them calculate it, and showing how it varies ,with the barometer. It is by repeating these questions over and over again, in a practical way, that they tell on the minds of children. Again, take a small square, or oblong, or a box of any shape a piece of wood hollowed out like a boat a tin, such as tarts and bread are usually baked in : floating these, and loading them with weights until the water reaches the edge they then see clearly that the quantity of water displaced is equal to the measure, in volume, of the vessel and the material of which it is made : and that a boat will just float, when the weight of the cargo and the weight of the boat taken together are equal to this displaced volume of the fluid in which it floats, and that any weight beyond this will sink it. Calculating the weight of this volume of water displaced, and subtracting from it the weight of the boat, gives the ex- treme weight which the boat would carry without sinking. JfATUEAL PHILOSOPHY. 107 Applying this to boats made of iron, or any other heavy metal, it is evident, that so long as the weight of the boat is less than a weight of fluid on which it is floating, the volume of which is equal to the whole size of the boat and material included, it will carry some cargo that the limit to the thickness of the iron, so that the whole may float, is that which would make the weight of the boat equal to the weight of fluid of its own volume that the thinner the material (due regard to safety being had), as in all cases the less the weight of the boat itself, of a given size, the greater cargo it would carry that a boat which would sink in one fluid would float merrily in another which was heavier, etc. ; for instance, a load which would sink in fresh would float in salt water, and be buoyant in mercury. The teacher would naturally point out that the same boat would carry ,a heavier cargo on salt water than on fresh. What would it be on oil, milk, mercury, etc. The number of things which the principles connected with floating bodies may be called upon to illustrate is very great. Having made them understand what is meant by the term specific gravity, and that by taking the weight of a certain volume of water as a standard, we calculate the weight of other bodies, it will be well to have a table of the specific gravities of substances in common use, metals, woods, etc., suspended on a cord in the schoolroom ; and to show them by experiment how these results are arrived at. It is quite a mistake to think that boys about twelve or thirteen years of age cannot be made to understand them, and not only that they will take a great interest in them. A short list is added, merely for the purpose of working an example or two from it. Taking water as 1 Distilled water T Sea water is.. 1-028 Platina 22-069 Gold 19-258 Mercury 13-586 Standard silver 10-474 Lead 11-352 Brass . , , 8-396 8'788 Coal . 1-250 Tin . 7-291 Oil . . . -940 Iron (cast) 7-207 Oak . ... . . . -925 Iron (bar) 7-788 Ash . . . -845 Zinc 7-100 Maple . . . . . . -765 Flint glass 3-329 Elm .. . . . '600 2-700 Fir . . . -550 Ivorv . 1-825 Cork.. 240 108 SUGGESTIVE HINTS. A simple inspection of this table may be made a useful lesson, by pointing out to them the comparative weight of those substances they are continually handling, the difference among them being much greater than they are in the habit of thinking it that those substances the specific gravity of which is less than 1 will float. In this way the com- paring one thing with another makes them think. Also why distilled water is a standard that water varies in weight with the substances it holds in solution that its boiling- point varies with these substances. Assuming the weight of a cubic foot of distilled water, and at the temperature of 63 Fahrenheit, to be 1000 ozs. (why distilled water and why a fixed temperature ?) let 1000 them show that the weight of a cubic inch = , and 1728 why the divisor is 1728. "When we speak of the specific gravity of lead being 11-352 and of iron 7'788, we mean that the weight of any given volume of lead or iron will be so many times that weight of the same volume of water, and knowing the one, the other is easily calculated. Thus a cubic foot of water weighs 1000 ozs., therefore a cubic foot of lead weighs 1000 ozs.X 11-352=11,352 ozs., of iron 1000 ozs. X 7'788, or 7788 ozs., o*f an inch in the same way. The specific gravity of dry oak is '925, of fir -550, of elm 600, therefore any given volume of these woods would float, being lighter than the same volume of water. A cubic foot of dry oak would be 1000 ozs. X '925, or 925 ozs. ; of fir, 1000 ozs. X '550, or 550 ozs., a little more than half the weight of oak. As applied to these substances, a good deal depends on their state of dryness, sap in them, etc. The following questions of a practical kind may suggest others : What is the weight of a block of marble, granite, etc., of regular figure (or any other which they can measure), base of it fifteen feet six inches by five feet two inches, and four feet high. NATUKAL PHILOSOPHY. 109 A given number of feet of oak, elm, ash, etc. ? A given mass of metal, what would be its' weight ? The weight of metals is exactly known from measurement, supposing them to be pure. In this way the scholar will be easily made to calculate what horse-power, or man-power moving power it will take to move given masses of these materials; and would, if called upon to put it into practice, contrive accordingly strengthening their machinery, etc., adapting it to the work required to be done. From this also may be shown, the reason why heavy bodies appear so much lighter when moved in a fluid like water the heavier the fluid the easier they move as when they raise a bucketful of water from, a well ; its in- creased heaviness the moment it gets to the surface of the water given size of the bucket how much increased in weight ? would it be heavier if raised out of the water into a vacuum, and how much ? moving masses of stone, as granite, under water floating beams of timber, etc. Having given the volume and the specific gravity of the fluid in which they are moving, to calculate what they lose in weight. Suspend a cubic foot of lead by a chain from one end of a balance : what weight would balance it at the other end, or over a single pulley ? A weight equal to itself. Now let it fall into a vessel of water : will it take the same weight to balance it as before ? No, sir, a weight less than itself, by the weight of a cubic foot of water. "What does a cubic foot of water weigh ? 1000 ozs. Well, I don't recollect the weight of a cubic foot of lead, but what is its specific gravity ? look at your table, 1 1 '352 ; therefore the weight of the lead in air is 11,352, and deducting 1000 ozs., the weight of a cubic foot of water, which is the weight lost by the lead, gives 10,352, the weight necessary to balance the lead when in water. Suppose a cubic foot of lead resting on a pile under water, what force must be exerted to pull it ofi\ supposing no resistance from friction on the pile ? About y'sths of its own weight. From this to explain how it is that the sand, stone, 110 SUGGESTIVE HINTS. sliingle, etc., are so easily tossed about on the sea-shore how the human body floats, etc. Questions : A vessel full of mercury, the bottom of which is nine inches by 4'56, and the height ten inches, what is its weight? Suppose a cistern, twelve feet long, five feet wide, and four feet six inches high, made of lead a quarter of an inch thick, what would be its weight ? What is the weight of a cylinder of iron thirty inches in diameter and six 'feet high ? Of a block of granite in the form of a circle, four feet six inches in diameter and twenty inches thick ? A statue of marble is placed in a vessel full of quick- silver, and causes six cubic feet to run over, what is its weight? Would it sink? "Would a statue offcast iron sink? Why is the line of the angler more likely to break after the fish is out of water than when it is in it ? Do you see any connection between the weight of a given mass of matter and the altitude of the barometer ? and how might a dealer in any bulky commodity profit by observing that connection ? The specific gravity of ice is to that of water as 8 to 9, and a field of ice of uniform thickness, has 10 feet above water, how many feet below it ? A cubic foot of a metal weighs 1000 Ibs. when weighed in air ; the weight of a cubic inch of air being about -g^th part of a cubic inch of water at a temperature of 63, what would be the weight of the body in vacuo ; also if weighed in water and if in air of half the density, work out the arithmetical results. Making them reduce the fluid measures into cubic inches, feet, etc., is a good exercise. How many cubic inches in a pint? 34-659. in a quart ? in a gallon, etc. ? Then of course they easily calculate the weight of any of these measures filled with a fluid, the specific gravity of which is given. In aeriform bodies, common atmospheric air is taken os a PHILOSOPHY. Ill standard instead of water, the weight of which is ahout one eight-hundredth part of the former : therefore, as a cubic foot of water weighs 1000 ozs., the weight of a foot of air will be a f