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other subject in the whole range of art that so thoroughly depends upon the judgment, the eye, and the power of the hand. There are very few practical rules which can afford us any help, except the general rules of proportion, and some knowledge of anatomy, which is indispensable; beyond these there is very little besides the all-important principle of arranging the work: therefore, before we give the rules relating to the proportions of the human figure, or say anything upon its anatomical construction, we must again repeat some of our former observations respecting the necessity of arrangement. Our pupils will remember how earnestly in the early lessons we advised them first to decide where the lines are to be drawn, and not to attempt the finished drawing until the positions of the lines are satisfactorily determined: the success or failure of their efforts will depend upon how far they follow or neglect this fundamental course of proceeding. We trust this once more repeated appeal to their practical sense and judgment will suffice, being ourselves assured that if they are really in earnest in their desires and endeavours to draw the human figure well, they will show their appreciation of this advice by following it out to the letter; for both master and pupil must now remember they have entered upon a noble, and at the same time a difficult subject.

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We have just observed that it is indispensably necessary to be acquainted with the various proportions of the human body, and to have some knowledge of anatomy. To these points we wish for a few moments to direct the attention of our pupils, and to place before them some powerful reasons why this course is so necessary. must be borne in mind that the human figure in its action is almost independent of any fixed laws; it is seen in every possible position, and under every form of expression; it is seen at rest, and in violent action; it is seen in its strength and in its weakness; it is seen in old age and childhood, in delicate womanly beauty and manly vigour. Then in addition to this there is the face, the index to the mind, subject to every variety of change resulting from inward emotions of joy or sorrow, revealing the best and the worst feelings of the heart-passion, despair, love, hatred, malice, revenge -and though last, not least, the various gradations of mental power, from the highest intellectuality to imbecility and madness. Surely here is a field for study which in its extent and grandeur has no rival. Now we wish our pupils thoroughly to understand that we are in earnest in what we are about to lay before them, and they must be in earnest also in their application. We are desirous to impart something more than a superficial knowledge of the human form; we wish to go thoroughly, as far as we can, into the subject, but at the same time it is not our intention to write a work upon anatomy in our drawing lessons; instead of this, we will recommend our pupils to study carefully the lessons upon this and kindred subjects which are to be found elsewhere in the pages of the POPULAR EDUCATOR. In these they will find quite

sufficient information for all they may require. Our object is only to open out a path for them to pursue, to point out other sources of information, and direct them in the way of applying the knowledge thus gained: therefore any of our pupils who do not care to

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enter into the subject to the extent we

propose may stop when they think fit; but as to those who desire to make their knowledge really useful for all practical purposes-and there are many engaged in the mechanical arts who will find it a great acquisition to be able to draw the figure well-we will en deavour not to disappoint them. When we consider how much this branch of art is required in decorating, stonemasonry, modelling, wood-engraving, and many other occupations, including all kinds of designing, we feel it incumbent on us not to allow so useful an addition to their education to be passed over lightly, and oblige them to lay our lessons aside, disappointed in not finding the instruction they require.

We will first give the relative proportions of the whole form, as represented in Fig. 119. The skeleton may be properly considered the framework upon which the whole body is built, and by which it is strengthened and supported; the proportion and height, the efficiency and freedom of the whole structure, depend principally upon the right formation of the skele ton; this hard and solid framework may be considered the timbers and beams of the superstructure, and the muscles which cover it are the ropes and pulleys for moving it; thus the framework is for strength, the muscles for action, and these determine the visible and varying outline of the body.

Taking the head as a standardthat is, from the crown to the chinthe whole length of the figure of a man may be considered as measuring seven and a-half or eight heads; of a child, the proportion will be according to its age; one of seven or eight years old may be allowed five and a-half heads; and an infant, nearly four. When the arms and hands are fully extended horizontally from the body, and if the distance between the tips of the fingers from the right hand across to the left be measured, it will be found equal in length to the whole body, so that a well-proportioned man can stand in a square frame and be able to touch the sides of the square respectively with his head, his feet, and the extremities of his fingers. The distance from the top of the shoulder-that is, from the head of the humerus, a (the upper bone of the arm)-to the elbow, b, is the same as from the elbow b to the first knuckle of the hand, c; the same distance occurs horizontally between the outer parts of the shoulders from a to d; from the top of the sternum (breastbone), e, to the navel f, the same; from the lower part of the breast-bone, g, to the pubis h (the bone across the lower part of the body), the same; thence to the top of the patella i (or small bone on the knee, generally called the knee-cap), the same; and from the lower part of the patella k to the instep m, the same. The knowledge of these uniform lengths, so repeatedly occurring, is a very material help in drawing the figure, preventing many doubts

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Fig. 119.

some instances they went even beyond this. We will not enter into any argument as to whether this modification of the facial angle indicated greater strength of mind and wisdom: it certainly has not been found to represent the standard of excel

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and difficulties. In the same way that the skeleton establishes the proportion and construction of the body, so in like manner does the skull, by its peculiarities of character and diversity of form, assist us to define and classify peoples, nations, and tribes, and also to decide upon their different intellectual capabilities. All must have noticed how very different the size of the human cranium or braincase is, when compared with the face, to that of the brute creation; and also that the head itself, comparatively speaking, undergoes very little change from growth: likewise that the brain almost reaches maturity at a very early period, and consequently the head of the infant is considerably larger in proportion to its body than when it has arrived at manhood; the cause of this is to be attributed to the brain only, in which there is less development, in proportion, than there is in the growth of the body. The face increases, but not to the same extent as the limbs and other parts. We remark in the infant head the smallness of the bones of the nose, the shallow jaw, and the elongated form of the head, having the brain-case large and projecting considerably behind. The roundness of the child's face is to be attributed to

Fig. 120.

the incompleteness of the lower part, which, as the teeth grow, expands from a greater extension of the jaw; when in old age the teeth have fallen out, and the face has contracted again, it resembles in many respects that of the child, excepting for the falling in of the

lips and the wrinkling of the skin. Thus as the child grows the face becomes elongated, and the proportionate difference between the length of the face and the depth from the forehead to the back of the head is less striking. The characteristic difference in the human head between the Grecian standard, as usually seen in ancient sculpture, and that of the negro,exists in the facial line. (See Fig. 120.) Draw a line from the lower part of the ear to the closing of the teeth in front, and from thence draw another to touch the outer projection of the forehead; this last line is called the facial line, and the two together form the facial angle the angle at e. The more acute this angle is, the nearer it approaches that of the

Fig. 121.

lower animals; the most desirable angle, as characteristic of the | higher powers of intellect, judgment, capability, and we include beauty also, is that of about 80°. The Grecian sculptors, in representing their gods, reached 90°, the right angle, and in

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lence in man. As the facial

angle formed by these two lines decreases, so we approach the negro, and when it is farther diminished we descend to the projecting jaws and smaller brain of the brute creation. (See Fig. 121, the facial angle of the cow.) These remarks are merely hints for the pupil, showing him the course he is to pursue in studying the human head. To go into a classification of the skulls of various tribes and nations, and point out the remarkable differences between them, is not our immediate object; to show there are these varieties, and to establish a standard as a base of construction, is all that is necessary: we leave our pupils to discover these differences for themselves, and resume our more legitimate subject-the method of drawing them. Now before we say anything about the proportions of the head and face, we wish to make a few observations upon the kind of drawing which belongs to the human figure

more than any other subject, and which will become more evident as we proceed. In drawing the human form, the term outline must be used in a far wider sense than that in which it is generally considered when it relates to inanimate objects or ornaments.

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Within the boundary line of any portion of the human form, be it face or limb, there is as great an amount of character and form to be expressed as in the outward or marginal line itself, and we cannot consider any one to be proficient who has not the power fully to represent it. The foreshortenings and projections of the body, and the unequal surfaces upon every part, arising from muscular action, as they press forward towards the eye, require an amount of anatomical knowledge which any one who attempted to draw them, without possessing, would soon discover to be indispensable. To confine our practice to the mere outline of the

human figure, would give but a small idea of what is meant by drawing it; children

do no more than this. To represent an advancing limb, or an uneven surface when placed directly before us, is quite another affair to that of representing the surface or limb when it is turned a quarter round, and is seen in profile. To acquire this

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pretend to sleep, he sleeps really (réellement). 5. Will you take a walk this morning? 6. I would do so with pleasure, if I had time. 7. Have you become acquainted with the physician? 8. I have not yet become acquainted with him. 9. How many questions have you asked (a) the child? 10. I asked him many questions. 11. Have you asked him if he had studied his lesson ? 12. I did not ask him. 13. Will not that little girl do her best to learn her lesson? 14. She will do her best to learn it. 15. Of what food do you make use when you are ill? 16. We make use of bread and rice. 17. Have you forgotten to bid farewell to your mother? 18. I had not forgotten it; I intended to go to her house this afternoon. 19. With whom have you become acquainted? 20. With the bookseller. 21. Do you not keep those ladies waiting? 22. I do not keep them waiting, they are not ready (prêtes). 23. Do I make you wait? 24. You do not make me wait. 25. done so (le). 27. Have you sent them out? Have you left your children in your room? Have you made purchases this morning? sent them out, I have let them remain where none, I have no money. 31. Has the servant made a fire in my room ? 32. He has made one. 33. Will you do your best to come to-morrow? 34. I will do my best to come early. 35. We travelled yesterday forty leagues in sixteen hours.

26. I have not 28. I have not they were. 29. 30. I have made

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3. Se faire mal conjugated reflectively, means to hurt one's

Vous avez fait vingt lieues en dix You travelled twenty miles in ten self. Se faire is used reflectively in the sense of the English

heures.

Nous ferons un tour de promenade.
Je lui ai fait plusieurs questions.
Ils nous ont fait leurs adieux.
Vous nous avez fait attendre.
Cet enfant fait semblant de dormir.
Vous faites semblant de lire.

[voir. Nous ferons notre possible pour le

Aise, glad.

Aliment, m., food. Crédit, m., credit. Demand-er, 1, to ask. Dorm-ir, 2, ir., to sleep. Etude, f., study.

hours.

We shall take a walk.

I asked him several questions.
They have bid us farewell.
You kept us waiting.

That child pretends to be asleep.

You pretend to be reading, or do as if you were reading.

We will do our best to see him.

VOCABULARY.

Se fâch-er, 1, ref., to be- Négociant, m., mor-
come angry.
chant.

Faire l'aumône, to give Quart, m., quarter.
alms.
Rarement, seldom.
Laiss-er, 1, to leave, let. | Réuss-ir, 2, to succeed.
Mendiant, m., beggar. Riz, m., rice.
EXERCISE 121.

1. Seriez-vous bien aise de faire connaissance avec ce monsicur? 2. J'en serais bien aise. 3. Ce cheval fait-il une lieue en un quart d'heure ? 4. Il a fait ce matin une lieue en douze minutes. 5. Leur avez-vous fait des questions? 6. Je leur en ai fait [Sect. XLI. 11; § 135 (7)]. 7. Quelles questions leur 8. Je leur ai demandé s'ils avaient fait des avez-vous faites ?

emplettes. 9. Vos élèves font-ils des progrès dans leurs études? 10. Ils n'en font pas beaucoup ils viennent rarement à l'école. 11. Si vous étiez chez vous, feriez-vous semblant de dormir? 12. Je ne ferais certainement pas semblant de dormir. 13. Pourquoi ne faites-vous pas entrer ce mendiant? 14. Ma mère vient de lui faire l'aumône. 15. Le négociant fait-il usage de son crédit ? 16. Il en fait usage. 17. De quels aliments ce malade fait-il usage? 18. Il fait usage de riz et de bouillon. 19. Faites-vous votre possible pour réussir? 20. Je fais tout mon possible. 21. Avez-vous fait entrer ces enfants, ou les avez-vous fait sortir ? 22. Je les ai laissés où ils étaient. 23. Vous avons-nous fait attendre ? 24. Vous nous avez fait attendre plusieurs heures. 25. Si vous faisiez attendre ces dames, elles se fâcheraient.

EXERCISE 122.

1. Does that child pretend to read? 2. He pretends to read. 3. Does not that gentleman pretend to sleep? 4. He does not

verbs to become, to turn. It is also used with the significa tion of the words cause, have, get, etc. Se faire takes être as its auxiliary [Sect. XLIV., § 46].

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ne fait-il pas le savant?

4. Il ne fait pas le savant, il fait le 6. fou. 5. Sied-il à ce jeune homme de faire le maître ici ? 7. Cela fait-il Il ne sied à personne de faire l'impertinent. quelque chose [R. 2 above] ? 8. Cela ne fait absolument rien. 9. Cela peut-il faire quelque chose à ces vignerons ? 10. Cela ne leur fait rien du tout. 11. N'êtes-vous pas bien chagrinés de cela ? 12. Nous en sommes bien fâchés, mais nous ne pouvons 13. Votre associé ne s'est-il pas fait bijoutier ? qu'y faire. 14. Non, Monsieur, il s'est fait peintre. 15. Cet artisan ne s'est il pas fait vitrier? 16. Il s'est fait tanneur, et son frère s'est fait soldat. 17. La modiste ne s'est-elle pas fait couper les cheveux ? 18. Elle se les ai fait couper. 19. Ne vous levez-vous pas aussitôt qu'il fait jour ? 20. Oui, Monsieur, je me lève de très-bonne heure. 21. Ne fait-il pas clair de lune? 22. Il fait très-clair, mais il ne fait pas clair de lune. 23. Fait-il bon vivre en Amérique ? 24. Il fait très-bon vivre en Amérique, les denrées y sont à bon marché.

EXERCISE 124.

1. Does not that gentleman play the learned man? 2. He plays the lord and fool at the same time (à la fois). 3. Does not that boy pretend to be ill? 4. He pretends to be ill, he does not wish to study his lessons. 5. When you have no wish to work do you pretend to be ill? 6. I never pretend to be ill. 7. Is it muddy to-day? 8. It is not muddy, it is dusty. 9. Will it be moonlight this evening? 10. It will not be moonlight, it will be very dark. 11. Is it comfortable here ? 12. It is very comfortable. 13. Is it too warm or too cold? 14. It is neither too warm nor too cold here. 15. Will you have your hair cut? 16. I had my hair cut yesterday morning. 17. Will you not go home, it is beginning to grow late? 18. Is it not very dark out (dehors) ? 19. It is not dark, it is moonlight. 20. Has not the glazier turned goldsmith? 21. He has not turned goldsmith, he has turned soldier. 22. Does that concern your brother? 23. That does not concern him. 24. Are you not sorry for that? 25. I am sorry for it, but I cannot help it. 26. Why do you get shaved? 27. Because I cannot shave myself. 28. Have you not hurt those children? 29. I have not hurt them. 30. Have you hurt your arm? 31. No, Sir, but I have hurt my head. 32. Has not your sister hurt her hand? 33. She has hurt her hand, and my mother has hurt her elbow. 34. Have you not hurt your head? 35. I have not hurt my head, but I have hurt my hand.

KEY TO EXERCISES IN LESSONS IN FRENCH.
EXERCISE 26 (Vol. I., page 107).

1. Êtes-vous plus attentif que votre sœur ? 2. Je ne suis pas aussi attentif que votre frère. 3. Avez-vous plus de courage que mon frère? 4. J'en ai tout autant. 5. Le maréchal a-t-il autant d'argent que de fer? 6. Il a plus de celui-ci que de celui-là. 7. A-t-il plus de modestie que l'Espagnol. 8. Il en a davantage. 9. Il en a plus que la sœur de votre ami. 10. N'avez-vous pas froid, Monsieur? 11. Non, Monsieur, mais j'ai peur et sommeil. 12. Le Hollandais a-t-il plus de fromage que l'Italien? 13 Il a plus de fromage et plus d'argent. 14. Avezvous autant de soie anglaise que de soie italienne? 15. J'ai plus de celle-ci que de celle-là. 16. Qui a plus d'amis que l'Espagnol ? 17. Votre ami en a plus. 18. L'Espagnol a-t-il autant de votre argent que du sien? 19. Il a moins du mien que du sien. 20. Avons-nous plus de manteaux de soie que de manteaux de drap? 21. Nous avons plus de ceux-ci que de ceux-là. 22. Avez-vous de bons manteaux ? 23. Oui, Monsieur, j'ai de bons manteaux, de bons chapeaux, et de bons souliers de cuir. 24. Avez-vous plus d'assiettes que de plats? 25. Je n'ai pas plus d'assiettes que de plats, mais j'ai plus de verres que d'assiettes. 26. N'avez-vous pas très-froid? 27. Non, Monsieur, je

n'ai ni froid ni chaud. 28. Votre charpentier a-t-il du bois? 29. Oui,

Monsieur, il a du bois, de l'argent, du fromage et de la viande. 30. Qui a plus d'argent que le charpentier? 31. Le Hollandais en a davantage. 32. Qui a plus d'estampes que de livres ? 33. Le libraire a plus de ceux-ci que de celles-là. 34. Êtes-vous aussi attentif que votre ami ? 35. Je suis plus attentif que mon ami.

EXERCISE 27 (Vol. I., page 115).

1. Is your dictionary very correct? 2. It is more correct than Boyer's. 3. Your dictionary is the most correct of all. 4. Which is the best of those gardens? 5. This is the best of all the gardens of the city. 6. Have you any more money? 7. I have no more money, but I have still some credit. 8. Have we more salad ? 9. We have

no more. 10. We have no more meat. 11. Who has more? brothers and sisters have some more.

12. My

13. Have you much more?

14. I have not much more. 15. Has your aunt more dresses than your niece ? 16. She has not many. 17. Is your nephew more learned than your niece? more learned than he.

18. He is not so learned as she. 19. She is 20. Are you still cold? 21. I am no longer 22. Have you no more news? 23. I have no cold, I am very warm. more. 24. Have you many? 25. I have but few. EXERCISE 28 (Vol. I., page 116).

1. Votre frère a-t-il un très-bon dictionnaire ? 2. Son dictionnaire n'est pas très-correct. 3. Votre père a-t-il plus de courage que lui? 4. Il a beaucoup plus de courage que votre neveu. 5. Vos frères ont7. Votre tante est-elle obligeante? ils du crédit? 6. Ils n'ont guère de crédit, mais ils ont de l'argent. 8. Ma tante est bien obligeante.

9. Avez-vous encore des livres, des plumes et du papier? 10. Je n'ai plus de livres, mais j'ai encore de bonnes plumes et d'excellent papier anglais. 11. Qui a encore du papier ? 12. Je n'en ai plus, mais mon frère en a encore. 13. Avez-vous des nouvelles, Monsieur? 14. Non, Madame, je n'en ai pas aujourd'hui. 15. Avez-vous autant de bois que le fils de mon frère? 16. J'en ai plus que vous ou que lui. 17. Avez-vous encore tort? 18. Non, Monsieur, je n'ai plus tort, j'ai raison. 19. Vos sœurs ont-elles encore faim? 20. Elles n'ont ni faim ni soif, mais elles ont encore sommeil. 21. Votre nièce est-elle aussi savante que lui. 22. Elle est plus savante que lui et que sa tante. 23. N'avez-vous pas de nouvelles, Monsieur ? 24. Non, Madame, je n'ai plus de nouvelles. 25. Qui a des nouvelles ? 26. Je n'en ai plus. 27. Les avez-vous toutes? 28. Oui, Monsieur, je les ai toutes. 29. Votre tante en a-t-elle encore beaucoup ? 30. Elle n'en a plus guère. 31. Votre frère a-t-il encore des chevaux anglais ? 32. Il n'en a plus. 33. Il en a encore deux. 34. Avez-vous encore un beau châle français ? 35. Je n'ai plus de châles français, mais j'en ai encore un anglais,

LESSONS IN CHEMISTRY.-VII.

WATER.

SYMBOL.. H2O-COMBINING WEIGHT. 18

As we have already seen, hydrogen, when it burns in air, enters into combination with the oxygen, forming water. The most direct way of proving this is by means of the Eudiometer, an instrument by which the composition of water is determined by synthesis.

A strong glass tube (Fig. 27) is hermetically sealed at one end, and through the glass two platinum wires are thrust when in its melted condition; these wires are opposite each other, and almost meet.

The tube is filled with mercury, and inverted into a bath of the same metal. A mixture of the gases, in the proportion of two volumes of hydrogen to one of oxygen, is passed into the tube, until the greater part of the mercury is displaced. The tube is now held firmly down with its mouth on a piece of sheet india-rubber; for if this were not done, when the gases explode the mercury would be driven out of the tube, and the experiment rendered fruitless. A Leyden jar is charged with electricity, a chain attached to one of the platinum wires is held against the outside of the jar, whilst with the knob the other wire is touched. The jar is thus discharged, a spark passing between the wires in the tube and exploding the gas. Upon releasing the pressure of the tube against the india-rubber, the mercury from the bath rushes into the tube, completely filling it, leaving only a small globule of water in the place of the tube full of gas.

The composition of water by analysis is easily determined by means of electricity. It is a well-known property of the gal vanic current that whenever it passes through water, the water is decomposed. The hydrogen passes with the current, and appears in bubbles at the negative wire, whilst the oxygen comes off from the positive wire. Fig. 28 indicates the arrangement for the experiment.

The two test tubes and the vessel are filled with water, to which is added one-eighth of sulphuric acid, to make the water a conductor of electricity. The test tubes are now inverted over the two leaves of platinum, h, n, which are connected with the screws A and B. To A is attached a wire from the platinum end of a Grove's battery, to в the wire from the zinc end. The electric current in the battery is generally said to pass from the zine to the platinum; it leaves the battery by the wire attached to the platinum, passes from the screw A through the water to B, and back to the zinc end of the battery. Because the current enters the instrument by the wire attached to A, that is said to be the positive wire, the other being the negative.

The gases as they rise from the plate are received in the tubes, and it will be found that the hydrogen is nearly twice the

volume of the oxygen. The reason why there is a little too much hydrogen is that oxygen is more soluble in water than hydrogen, and as the gases rise through the water more oxygen is retained than hydrogen.

It was said in the last lesson that the escape of hydrogen from the surface of zinc when in acidulated water was really due to galvanic action. It is a most difficult thing to get zinc perfectly pure; in the ordinary metal, the surface is composed of particles of pure and of impure zine. If now any two different metals be acted upon by dilute acid, a current of electricity will be developed, so that over the zinc surface there are thousands of "galvanic couples." A particle of pure metal and its neighbour of impure metal forming a "couple," between the two a current begins to circulate, and as it passes the water is decomposed the hydrogen escapes from one particle and the oxygen attacks the other.

If zinc be amalgamated-that is, if the surface be rubbed with mercury these particles are formed into a paste, and intimately mixed, so that the whole surface becomes impure, and therefore amalgamated zinc will not liberate hydrogen. For this reason the zinc plates in galvanic batteries are always amalgamated.

Fig. 27.

The other method of getting hydrogen in large quantities will suggest at once another means of analysing water. If the porcelain tube and its contents, the iron turnings, be carefully weighed, and also the water in the flask, and then the tube, after the whole of the water has been sent over the red-hot turnings, be also weighed, the difference will evidently be the weight of the oxygen, which has combined with the iron, or the weight of the oxygen which was in the water; the difference between this and the whole weight of the water will give the hydrogen.

It will at once occur to the student that the "reduction' of black oxide of copper by hydrogen offers a fourth means of determining the constitution of water. By weighing the "reduction tube" and its contents before and after the experiment, the weight of oxygen given off by the cupric oxide will be ascertained, and also the weight of the water formed be known. It will also be found that 88-89 parts of oxygen by weight unite with 1111 parts of hydrogen to form 100 of water. The oxygen and hydrogen, in entering into combination to form water, produce a very high degree of heat. This has been taken advantage of in the "oxy-hydrogen blow-pipe." Two strong india-rubber bags are filled with the gases, which are carried by separate tubes to the burner. The mixed gases issue through a fine nozzle, and when lit they burn with a pale nonluminous flame, which has a very high temperature: wire, watch-springs, etc., are melted immediately, and in many instances the metal scintillates beautifully.

Fig. 28.

When the jet is directed on a piece of lime, the lime is raised

to such a white heat as to produce one of the most brilliant of lights-the oxy-hydrogen light. The best arrangement is the one sketched in Fig. 29. In this manner it is used for magiclanterns; the stand sliding into the bottom of the lantern, the handles, D and c, remaining outside. Instead of hydrogen, ordinary coal-gas is generally used. The greatest care must be taken after each exhibition to empty the bags, H, o, lest, when they are re-filled, the oxygen should by any chance be put into the hydrogen-bag, when a very violent explosion would be the consequence.

The gases mix in B, & brass tube, which is packed with fine wire gauze. The cylinder of lime, L, is supported on a wire which is threaded with a screw which passes through a collar soldered between the two tubes. By this wire the lime can be turned or raised, for after a time the jet burns a hole in the lime.

For a further precaution it is well to have a differently shaped handle, c, for the oxygen. It is possible to burn the gases mixed from one bag, through Hemming's Safety Jet, which is simply a brass tube packed with discs of fine wire gauze; but the flame has been known to pass down through forty of these discs before it was extinguished by their cooling action. It is therefore more safe to burn the gases from separate bags.

If we follow water in passing through its three states, we shall discover many strange properties. If a piece of ice be placed in a vessel over a fire, with a thermometer, the thermometer will rise or fall until it reaches 0° Cent., when the ice will begin to melt. Although heat is continually passing from the fire into the vessel, yet the thermometer will remain at 0° until the last particle of ice has disappeared. Where, then, has all this heat gone? It has gone to do a certain work, to turn the solid into a liquid, and because this heat does not affect the thermo

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meter it is called "latent heat." To measure this "latent heat" we must have some standard. We cannot speak of a mètre or a litre of "caloric; " therefore the unit of heat, or the measure of heat, is that amount of heat which is required to raise a unit of water 1° Cent. The latent heat of water is 79 of these thermal units; that is to say, to melt a kilogramme of ice, which is at 0° Cent., requires as much heat as it does to raise 79 kilogrammes of water 1°.

Every solid upon assuming the liquid condition renders latent a certain quantity of heat; and every liquid becoming a solid gives out its latent heat.

Let sodium sulphate be added to boiling water until the water will dissolve no more, and then allow the water to cool; if undisturbed the salt will not crystallise, but upon stirring it with a thermometer, a large quantity of the Glauber salt will assume the solid state, and a rise in the temperature will be indicated by the thermometer.

The fact that a solid cannot pass into a liquid without rendering "latent" a certain quantity of heat, has been taken advantage of to form freezing mixtures. Whenever a solid is so acted upon by another solid or a liquid as to be compelled to assume a liquid condition, heat must be taken from surrounding bodies. Snow, or powdered ice, and salt liquefy each other, and produce the temperature of Fahrenheit's zero. Ammonium nitrate and an equal weight of water will offer an example of a freezing mixture in which one of the bodies is already in a liquid condition. If either of these mixtures be made in a test tube, moisture will first condense on the outside and then freeze. If ice be required in some quantity, a thin dish containing water is placed in the mixture.

In the raising of the temperature of water from 0°, a very remarkable exception to an otherwise universal law is observed. All bodies expand when heated; but upon heating water st 0° Cent. it contracts until it reaches 4° Cent., and from this point

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