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LEES ITENS-IIII. 190t be BOTION H.-5. 29 NXITS. med. sidence: LTE s

- 272. . - : esperes, te kope; being that car to see ; sac mers -Edressing artis mething certain

Come only and positive. Pewted sex songtei firmatively, and in temperatures Cosis will remain late que 112 Eem: silowed the bestive present ce future of time, when one hanted to s ces [5127 (2) jote

e combustion of the hydrogen
ose the carbon to this

2. The above rerbs. when zsed in the same connection and
of this bent te viermcted-
hose side to be carbon subjunctive 3 1972

conjugated segatively interrogatively, are followed by the stion, and is therefore depo

Je ne crois pas qr'] Fienne, I do not believe he will come. ch of the cold ais passes 3. & verb, preceded by another serb and by a relative premeisie st the sense of noun, is pat in the subjunctive while there is an idea of ansebastien of the bringen, thus certainty, and in the indicative when the idea is certain [S 127 Se the completa combustion of (2) Note),

me.

come.

-asse

-Usse

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un

J'ai un homme qui me rendra ser- I have a man who will oblige me. know that he depends upon you. 25. Does not that gentleman vice,

depend upon me? 26. I think that he depends upon your J'ai besoin d'un homme qui me I want a man who will (may) oblige brother. 27. Will the porter soon come in again ? 28. I hope rende service,

that he will not tarry long. 29. Will you not lend me your 4. A verb preceded by a superlative, relative, or by the umbrella ? 30. I will lend it to you with pleasure. 31. Does Fords le seul, le premier, le dernier, is put in the subjunctive my brother remain standing ? 32. He does not wish to sit [$ 127].

down. 33. Do you wish me to sit down ? 34. I wish you to Voilà le seul chapeau que j'aie, That is the only hat I have.

remain standing. 35. I wish that he may come. Voilà le meilleur homme que je There is the best man I know. connaisse,

SECTION LXXIV.-THE IMPERFECT AND PLUPERFECT RÉSUMÉ OF EXAMPLES.

OF THE SUBJUNCTIVE. Je crois que le concert a eu lieu. I believe that the concert took place.

1. The terminations of the imperfect of the subjunctive are Je ne pense pas que notre ami I do not think that our friend will in all the verbs, regular and irregular, of the four conjugations, vienne.

sse, sses, t, ssions, ssiez, ssent. J'espère que vous apprendrez cela I hope that you will learn that by 2. The vowel preceding the t of the third person singular par coeur.

heart.

always takes the circumflex accent. Je ne pense pas qu'il puisse appren. I do not think that he can learn all dre tout cela par cæur. that by heart,

3. CONJUGATION OF THE IMPERFECT OF THE SUBJUNCTIVE Je crois que ce marchand s'enrichit I believe that this merchant grows

OF THE REGULAR VERBS. aux dépens d'autrui.

rich at the expense of others.

Que je chant

fin
-isse
reç

rend -isse. Je ne crois pas qu'il s'enrichisse à I do not believe that he enriches him.

That I might sing

might finish might receive might render. vos dépens.

self at your expense.
Que tu parl -asses chérisses

aperç -asses vend Je ne crois pas que vous réussissiez I do not believe that you will succeed that thou mightest speak

-isses.

mightest che- mightest pere mightest sell. å gagner votre vie. in earning your living.

rish

ceive J'ai une carafe qui contient un litre. I have a decanter which

holds a litre. Qu'il donn

fourn -it

tend -1t. Je cherche une carafe qui contienne I seek a decanter which holds a

That he might give might furnish might gather might tend. un litre.

litre.

Que nous cherch -assions pun issions oonç -ussions entend-issions. Je vous prête le meilleur chapeau I lend you the best hat I have, on

condition that you will return it Que vous port

That we might seek que j'aie, à condition que vous

might punish might conceive might hear.

-assiez sais -issiez d - ussiez perd -issiez. me le rendiez demain.

to me to-morrow.

That you might carry

might seizo might owe might lose. VOCABULARY.

Qu'ils aim

-assent .issent des -Ussent mord -issent. S'asse-oir, 3, ir., ref., to Fort, strong.

Rentr-er, 1, to come in

That they might lovo might unite might deceive might bite. sit down. Litre, m., litre, about a again.

4. This tense may be formed from the past definite [Sect. Compt-er, 1, to depend. quart.

Sorte, f., kind.

L.) by changing, for the first conjugation, the final i of the Cristal, m., crystal. Négociant, m.,merchant Suffi-re, 4, ir., to suffice. first porson singular of the past definite into sse, sses, etc., and Debout, standing. Parasol, m., parasol. Tanneur, m., tanner. Dur-er, 1, to wear, last. Portier, m., porter. Tard-er, 1, to tarry.

by adding se, ses, etc., to the same person in the other three

conjugations. This rule has no exceptions. EXERCISE 141.

J'allai, j'allasse ; je finis, jo finisse. I went, I might go; I finished, I 1. Pensez-vous que ce drap dure longtemps? 2. Je crois

might finish. qu'il durera bien, car il est fort. 3. Croyez-vous que notre 5. All the observations made in Sect. LI., on the changes of portier tarde à rentrer ? 4. Je crois qu'il ne tardera pas. 5. the stem of the irregular verbs, in the past definite, apply equally Désirez-vous que nous restions debout? 6. Je désire, au con

to the imperfect of the subjunctive. traire, que vous vous asseyiez. 7. Croyez-vous que ces étudiants

6. The pluperfect of the subjunctive is formed from the impuissent apprendre cinq pages par cour en deux heures ? 8. perfect of the same mode of one of the auxiliaries avoir, être, Je crois que c'est impossible. 9. Espérez-vous que notre ami and the past participle of the verb :: arrive de bonne heure ? 10. J'espère qu'il arrivera bientôt. 11. Quelle sorte de carafe vous faut-il ? 12. Il m'en faut une

Que j'eusse fini; que je fusse venu. That I might have finished; that I

might have come. qui contienne un litre. 13. J'en ai une de cristal qui contient deux litres. 14. Pensez-vous que ce négociant s'enrichisse à

7. All the rules given on the use of the subjunctive in the vos dépens ? 15. Je sais qu'il s'enrichit aux dépens d'autrui. three preceding sections, apply, of course, to the imperfect and 16. Quel parasol pensez-vous me prêter ? 17. Je pense vous pluperfect of the mode. prêter le meilleur que j'aie. 18. Le tanneur réussira-t-il à gagner

8. In the same manner as the present or future of the insa vie ?

19. Je ne crois pas qu'il y réussisse. 20. Pensez-vous dicative of the first part of a proposition governs, under the que cet argent suffise à votre père ? 21. Je crois qu'il lui suffira. above-mentioned rules, the verb of the second part, in the 22. Croyez-vous que ces messieurs comptent sur moi ? 23. Jo present or past of the subjunctive; so the imperfect and other sais qu'ils comptent sur vous. 24. Pensez-vous que le concert past tenses of the indicative, and the two conditionals, govern ait lieu aujourd'hui ? 25. Je crois qu'il n'aura pas lieu. the verb in the second part of the proposition, in the imperfect

or pluperfect of the subjunctive. EXERCISE 142.

Ne fallait-il pas que je lui parlasse? Was it not necessary that I should 1. Do you believe that the concert has taken place ? 2. I

speak to him? believe that it has taken place. 3. Do you believe that your Il faudrait que je lui donnasse ce It would be necessary for me to give sister's dress will wear well? 4. I think that it will wear livre,

him that book. well, for the silk is very good. 5. Do you believe that our friend will succeed in earning a livelihood ? 6. I believe that

RÉSUMÉ OF EXAMPLES. he will succeed in it (y), for he is very diligent. 7. Do you Voudriez-vous que je donnasse un Would you wish me to give that child think that the tanner grows rich at my expense ? 8. I think

coup de bâton à cet enfant ?

a blow with a stick?

I would wish you to fire your gun at that he enriches himself at the expense of others. 9. Does Je voudrais que vous tirassiez un

coup de fusil sur cet oiseau.

that bird. the merchant grow rich at my father's expense? 10. He Exigeriez-vous que nous revinissi. Would you require us to return early ? grows rich at your expense. 11. What kind of a house must

ons de bonne heure ? you have (vous faut-il)? 12. I must have a house which has Que voudriez-vous que ces hommes What would you wish those men to ten rooms. 13. I have a good house which has twelve rooms. fissent?

do ? 14. What kind of decanter do you seek ? 15. I look for one Que vouliez-vous que je fisse ? What did you wish me to do? that holds three litres, 16. I have one which holds two litres, Il faudrait que j'eusso mon argent? It would be necessary for me to have I will lend it to you. 17. What coat will you send me ?

18.

my money? I will send you the best I have; take care not to stain it. 19. Je ne voulais pas que vous mourus. I did not wish you to die with cold.

siez de froid. Do you think that the student will learn all that by heart ?

Elle craignait que vous ne mourus- She feared lest you might die with 20. I do not think that he will learn it. 21. Do you believe

siez de misère et de faim.

want and hunger. (that) he will come ? 22. I believe that he will come soon. Voudriez-vous que je jetasse un Would you wish me to cast a glance 23. Do you think that your father depends upon me ? 24. I coup d'eil sur ces papiers ? upon these papers 1

VOCABULARY.

27. J'aime les livres. 28. Avez-vous envie d'apprendre le rosse ? Bécasse, f., woodcock. Ivrogne, m., drunkard. Ressembl-er, 1, to re

29. Je n'ai pas envie d'apprendre le rasse. 30. N'avez-vous pas le Bord, m., shore. Lièvre, m., hare.

semble.

temps? 31. Je n'ai guère de temps. 32. Qu'apprenez-vous ? 33. Nous Charg-er, 1, to load. Mer, f., sea.

Rétablissement,

m.,

apprenons le latin, le grec, le français et l'allemand. 34. N'apprenezCoup, m., blow. Mour-ir, 2, ir., to die.

vous pas l'espagnol ! 35. Nous ne l'apprenons pas. 36. Avez-vous de

recovery. Coup de fusil, m., shot. Perdrix, f., partridge. Santé, f., health.

belles fleurs dans votre jardin? 37. Nous avons de très belles fleurs ; Tir-er, 1, to fire, shoot.

nous aimons beaucoup les fleurs. Coup-d'oeil, m., glance. Poste, m., post.

38. Les lui donnez-vous ? 39. Je Se rend-re, 4, ref., to Voul-oir, 3, ir., to will,

vous les donne. 40. Donnez-nous-en. Demi-usé, half-worn.

41. Ne nous en donnez pas. Fouet, m., whip. repair. . to desire.

EXERCISE 55 (Vol. I., page 294).
EXERCISE 143.

1. Whom do you know? 2. We know the Dutchman of whom you 1. Voudriez-vous que j'achetasse un habit à demi-usé ? 2. speak to us. 3. What lessons are you learning ? 4. We are learning Je voudrais que vous en achetassiez un neuf. 3. Voulait-on the lessons which you recommend to us. 5. Is what I tell you true! que ce soldat malade se rendît à son poste ? 4. On voulait qu'il 6. What you tell us is true. 7. Of whom do you speak to us! 8. We se rendit à son régiment. 5. Faudrait-il que je demeurasse au speak to you of the Scotchmen who are just arrived. 9. Do you know bord de la mer? 6. Il faudrait pour le rétablissement de votre who is just arrived? 10. I know that the gentleman with whom your santé que vous vous restassiez en Suisse. 7. Ne pensez-vous 12. They do almost nothing, they have almost nothing to do. 13. What

brother is acquainted is just arrived. 11. What are your sisters doing? pas que cet enfant ressemble à sa mère ? 8. Je ne pense pas do you put into your trunk ? 14. We put what we have, our clothes qu'il lui ressemble. 9. À qui ressemble-t-il? 10. I ressemble and our linen. 15. Do you not put your shoes! 16. We put in the à sa sæur aînée. 11. Consentiriez-vous que votre fille éponsât shoes which we want. 17. What do you want? 18. We want what we cet ivrogne ? 12. Voudriez-vous que nous mourussions de have. 19. Does that child know what he is doing! 20. He knows misère ? 13. Je craignais que ces dames ne mourussent ($ 127 what he does and what he says. 21. Will you not tell them of ite? (8), Sect. LXXI., 9] de froid. 14. Ne voulez-vous pas tirer sur 22. With much pleasure. 23. Are you doing what the merchant orders?

25. He speaks of that of which you ce lièvre ? 15. Je tirerais sur cette bécasse si mon fusil était 24. We do what he tells us.

speak. chargé. 16. Combien de coups de fusil voudriez-vous que je

EXERCISE 56 (Vol. I., page 294). tirasse ? 17. Si vous aviez de la poudre, je voudrais que vous

1. Avez-vous ce dont vous avez besoin? 2. Nous avons ce dont tirassiez sur cette perdrix. 18. Voulez-vous que je jette un coup

nous avons besoin. d'oeil sur cette lettre ? 19. Je voudrais que vous la lussiez. 4. La dame dont vous parlez est ici. 5. Vient-elle d'arriver? 6. Elle

3. Le monsieur que vous connaissez est-il ici ! 20. Que voudriez-vous que je fisse ? 21. Je voudrais que vous vient d'arriver. 7. Connaissez-vous ce monsieur ? 8. Je connais le fissiez attention à vos études. 22. Faudrait-il que je sortisse ? monsieur qui parle avec M. votre père. 9. Savez-vous son nom ? 23. Il faudrait que vous restassiez à la maison. 24. Que 10. Je ne sais pas son nom, mais je sais où il demeure. 11. Que faites. voudriez-vous que je fisse à ce cheval ? 25. Je voudrais que vous tous les matins ? 12. Nous ne faisons presque rien, nous n'avons vous lui donnassiez des coups de fouet.

presque rien à faire. 13. Le tailleur fait-il vos habillements ? 14. 11

fait mes habits, ceux de mon frère et ceux de mon cousin. 15. SavezEXERCISE 144.

vous ce que vous dites ? 16. Je sais ce que je dis et ce que je fais. 1. What would you have me do? 2. I wonld have you cast 17. Connaissez-vous l'Ecossais dont parle M. votre frère ? 18. Je le

19. Que met-il dans son coffre? 20. Il y met ses habil. a glance upon this letter. 3. Would you wish me to give that lements. 21. Ce que vous dites est-il vrai? 22. Ce que je dis est dog blows with a stick? 4. I would wish you to give that vrai. 23. Comprenez-vous ce que je vous dis ? 24. Je comprends horse blows with a whip. 5. Would you require us to return tout ce que vous dites. 25. De qui M. votre frère parle-t-il? 25. Il at five o'clock? 6. I would require you to return early. 7. parle du monsieur dont la seur est ici. 27. M, votre frère a-t-il tort Do you think that your brother resembles your father? 8. I de faire ce qu'il fait ? 28. Il ne peut avoir tort de le faire. 29. Que do not think he resembles my father. 9. Whom do you think faites-vous ? 30. Je fais ce que vous faites. 31. Où mettez-vous mes he resembles ? 10. I think he resembles my mother. 11. livres ? 32. Dans le coffre de M. votre frère. 33. M. votre frère estHow many shots have you fired? 12. I have fired five shots il ici? 34. Il n'est pas ici. 35. Il est chez mon frère ou chez mon at that woodcock. 13. Would you not have me fire at that partridge? 14. I would have you fire at that partridge, if your gun were loaded. 15. Where would it be necessary for

HYDROSTATICS.-I. me to dwell? 16. It would be necessary for you to dwell on the sea-shore. 17. Would you have me die with hunger ? 18.

OBJECTS OF THE SCIENCE-PRINCIPLE OF EQUALITY OF I would not have you die of hunger. 19. Would you have

PRESSURE—HYDROSTATIC PRESS. your brother die with cold? 20. I would not have him die The branch of Natural Philosophy the study of which we are with cold or want. 21. What would you have your son do? now about to commence is called Hydrostatics, and it is con22. I would have him learn his lessons. 23. Would you have cerned in examining the conditions of equilibrium in liquids

, the him learn German? 24. I would have him learn German and pressures they exert, and their motions ; just as Mechanics wat Spanish. 25. Have you fired at (sur) that hare? 26. I have concerned with solid bodies. not fired at that hare. 27. Would it be necessary for me to go out ? 28. It would be necessary for you to go out. 29. Would or the gaseous ; and the sciences of Mechanics, Hydrostatics,

All matter exists in one of three states the solid, the liquid, it be necessary for me to remain here? 30. It would be neces. and Pneumatics treat respectively of its motions and the forces sary for you to go to church. 31. What did you wish ? 32. which act upon it in these three states. We must not, however

, I wished you to write to me. 33. Did you wish me to buy a imagine that a body can exist in only one of these conditions

, coat half worn out ? 34. I wished you to buy a good hat.

for many assume at different times all three. To take the

simplest illustration, water is best known to us in a liquid state, KEY TO EXERCISES IN LESSONS IN FRENCH.

that being the one in which we most commonly meet with it;

but if a certain amount of heat be taken away from it, it will EXERCISE 54 (Vol. I., page 276).

become changed into a solid, which, though to distinguish it, we 1. Notre médecin sait-il le français ? 2. Il sait le français, l'anglais call ice, is not a new substance, but merely the water in a et l'allemand. 3. Connait-il le médecin français ? 4. Il le connait très

different state. So also an increase of heat will change the bien. 5. Connaissez-vous cette dame? 6. Je ne la connais pas.

water into an invisible gas or vapour which we call steam. In 7. Est-elle allemande ou suédoise ? 8. Elle n'est ni allemande

ni this case heat is the agent which produces these changes of suédoise, elle est russe. 9. Avez-vous l'intention de lui parler ? state, and it does so by driving the ultimate particles of the 10. J'ai l'intention de lui parler en anglnis. 11. Sait-elle l'anglais ? substance farther apart from each other. Many of the metals 12. Elle sait plusieurs langues; elle parle anglais, danois, suédois et hongrois. 18. Monsieur votre frère est-il colonel? 14. Non, Monsieur, heat, and hence can be melted and cast into moulds of any

as is well known, assume the liquid state under the influence of il est capitaine. 15. Votre tapissier est-il danois

? 16. Il n'est pas desired shape. If they be exposed to a much higher degree of je suis hongrois. 19. Savez-vous le chinois? 20. Je sais 1. chinois,T: heat, as may be done in the electric lamp, they, too, will become russe et le greo moderne. 21. Avez-vous tort d'apprendre les lan

converted into vapour. 30 Je n'ai pas tort d'apprendre les langues. 23. Connaissez- The difference between these states depends upon the rela

qui demeure chez Monsieur votre frère ? 24. Je le tions existing between the ultimate particles of which the

70 le connais pas. 26. Aimez-vous les livres ? masses are composed. In a solid these particles have a strong

père.

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attraction for each other, that is, cling closely together, and sure is transmitted equally and with equal force in all directions. resist any effort to separate them. Many of the metals can be A little explanation will make this clear. If we have a solid drawn out into fine wires, and yet will sustain considerable cylinder made to fit exactly and move without friction in a tube, weight before the attraction or cohesion, as it is termed, is over and we press with any force against one end of it in a direction come. If we take two lead bullets, and scrape a portion of the parallel to its length, the pressure will be transmitted unsurface of each so as to render them even, and then by pressing diminished to the other end, and will there act against any them firmly together, drive out the air, this cohesion will obstacle just as if the cylinder were not interposed; no prescause them to cling to each other so tightly as to require a con- sure will, however, be exerted against the side of the tube. If siderable degree of force to separate them. Another property now the cylinder be removed and the tube filled with water, of solids which results greatly from this, is the amount of fric- a piston being made to fit each end of it, any pressure exerted tion with which their ultimate particles move over one another. on one end will, as before, be transmitted to the other, but a In some solids this is so great that no moderate degree of force similar pressure will also be exerted against every part of the will suffice to move them or to alter the form of the mass. In inner surface of the tube. If the surface of the piston have an this respect there is, however, a great difference between solids, area of one square inch, and a pressure of 10 pounds be exerted for they merge so gradually into liquids that it is difficult to on it, every square inch of surface in the cylinder will sustain a draw a well-defined line separating them.

similar pressure; and if we insert into any part of it a tube In liquids both these properties are present in a much smaller with a piston one square inch in area, this piston will be forced degree. The cohesion of the particles is so much less that out with a pressure of 10 pounds. If the tube be bent or twisted scarcely any force is required to separate a mass of liquid into in any direction, the pressure is still transmitted exactly as if it portions; in fact, it falls apart from its own weight, unless it were perfectly straight. This property of liquids follows from be put into some vessel capable of containing it, and it imme- the fact of their particles moving without friction, and is of diately assumes the shape of such a vessel. The same, however, great practical importance. In Mechanics, even with the best might be said of a heap of fine powder : how then does this and most flexible ropes and chains, there is always a great loss differ from a liquid? The difference consists, first, in the fact from friction and rigidity, but by means of a liquid a pressure that there is a large amount of friction between the atoms of can be transmitted in any direotion without sensible loss. powder, so that if placed in a heap they do not spread them- Similarly, if we have a closed vessel with several equal openselves out as particles of liquid would; and next, in the ings in it, in each of which a piston of one inch diameter works, a ultimate atoms of the liquid being so minute as even under the pressure of 10 pounds on one will cause a similar pressure on each most powerful microscope to be invisible, while those of the of the others. If now another piston be fitted to the vessel, powder have a definite size. The property the particles have 10 inches in diameter, a pressure of 10 pounds will be exerted on of moving over one another with scarcely any friction is one of every portion of its surface equal in area to the smaller piston. very great importance, and accounts for several of the pheno- Now the areas of circles are proportional to the squares of their mena we shall meet with.

diameters; the area of the larger piston is therefore 100 times If we now look at the case of a gas we shall find that not only that of the small one, and the total pressure on it is therefore is there no cohesion between the particles, but they repel one 100 x 10, or 1,000 pounds. We have thus what we may consider another, and, unless confined, will fly apart as far as possible. as another mechanical power, a gain being effected by the use If a cubic inch of any gas be placed in a large box, it will im- of it as there was by the lever. The principle of virtual velomediately fill it and become equally distributed in every part. cities holds good here as well as in the powers we previously conThere is also this further difference between liquids and gases, sidered; for if the small piston be forced in 1 inch, it is clear that that whereas a gas may be compressed almost indefinitely, re- the other will only be moved to the extent of oth of an inch, gaining its former bulk on the pressure being removed, a liquid and thus, though 100 times the pressure is exerted, it is only is for all practical purposes incompressible.

through oth part of the space. A simple experiment can It was for a long time believed to be absolutely so, but it has easily be tried to show that this pressure is transmitted upwards since been found that a pressure equal to that of the atmo- as well as in other directions. Procure a tube of large diameter, sphere, or 15 pounds per square inch, will cause a compression and grind one end of it flat, so that it can be closed by a disc of in water to the extent of 40 or 50 millionths of its bulk. The glass fitting closely against it. Fasten a piece of string to the simplest way of ascertaining this is to procure a cylinder closed middle of this disc, and pass the end up through the tube, so at one end, and having a piston fitting very tightly into it. This that by holding the string it may be kept in its place. If the is filled with water, and a spring ring placed just under the whole be now lowered into a vessel of water, the upward prespiston, so that if it be driven in at all, the ring will remain sure will keep the disc in its place without the string being at the part of the cylinder which it reached, and thus show the held; but on the tube being gradually raised till the end comes extent of the compression. The apparatus thus arranged is nearly to the surface, the pressure will diminish until it will fixed to a heavy weight, and by means of a cord lowered to a be unable any longer to sustain the disc, which will then fall to known depth in the sea. The pressure, as will be seen increases the bottom. with the depth, and the position of the ring will indicate the This principle of equality of pressure leads to many strange extent of the compression.

and important results. The apparatus known as the hydroHaving thus cleared our way, we can enter more directly on static bellows, and represented in Fig. 1, is an interesting the science itself. It is usually divided into two branches- illustration of it. Two circular boards, A, B, are connected to hydrostatics proper and hydrodynamics; the former treating gether by flexible sides, so as to form a circular pair of bellows. of the equilibrium of liquids and the pressures they produce, A long tube opened out at the upper end into the shape of a while the latter has to do with their motions. The term funnel is made to open into this. The whole arrangement is hydraulics, derived from two Greek words meaning "water" then partly filled with water, not, however, so much so as to and “a pipe,” is sometimes used instead of hydrodynamics, but it fully expand the bellows. If now several heavy weights be is more strictly applied to the raising of water by means of placed upon the upper board, and water be poured down the tube, pipes ; we shall, however, use it in its more extended meaning. the weights will be raised. A man may even stand on the

Water is by far the most common of all liquids, and hence board, and, if the tube be long enough, be raised by pouring in will be taken as a type. In its physical properties, however, a jug of water. Let us suppose that the area of the tube be it differs little from other liquids, and what is said of it half a square inch, and that of the board 1 foot, and that a may, with the necessary modifications, be applied to liquids pound of water be poured into the tube. The pressure on the generally.

bottom of the tube is, of course, 1 pound; and a similar pressure We found in Mechanics that though the lever and other is exerted on every half a square inch in the inner surface of mechanical powers possessed weight, we could understand their the bellows. Now the surface of the board is 144 square principles better by neglecting it at first; just so here it is easier inches, the pressure produced on it by the pound of water is to omit at first all notice of the weight of the liquid.

therefore 288 pounds. On account of the great apparent gain The fundamental principle of hydrostatics is that of the this is sometimes called the Hydrostatic Paradox, but on conequality of pressure, or, as it is sometimes called, after the sideration it is seen to be no more paradoxical than the gain philosopher who first stated it, Pascal's law. It is as follows: effected by any other mechanical power; as, always, what is -If any pressure be exerted on any part of a liquid, that pres- / gained in power is lost in time.

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In a similar way, if a cask be filled with liquid, and a long The advantage gained by the machine depends upon two tube be inserted tightly into the top and filled also, the weight things : first, the comparative sizes of the pistons; and second, of water in this tube, though trifling in itself, will exert such a the proportion between the distances A B and H B. Suppose, pressure as to burst open the cask. If the diameter of the for example, that the diameter of K is 15 inches, and that of D pipe be rather over one-third of an inch, its area will be half an inch; also that the length of A B is 3 feet and B about one-tenth of a square ineh, and 2 pounds of water poured 2 inches, what power will a man pressing at a with a force of into it will fill it to a height of about 46 feet. This will cause 50 pounds exert? Since the diameters are in the proportion of a pressure of 20 pounds per square inch ; and

1 to 30, their areas are in the proportion of 1 to as the surface may have an area of about 2,000

900, and therefore whatever pressure is exerted square inches, the total pressure produced by

Fig. 3.

on D, K sustains 900 times the amount. Bat the 2 pounds of water will be about 40,000

A B is a simple lever of the second kind, and pounds, a pressure sufficient to burst almost any

the gain produced by its use is , or 18. The cask. For this reason, when the parts of a town

pressure of 50 pounds at a produces, therefore, lie at different levels, and the water is supplied

one of 900 on D; and thus the total force with from a reservoir situated in an elevated part,

which the books at m are compressed is 900 x the pipes have to be made very strong, as they

900 = 810,000 ponnds, or upwards of 360 tons. have to sustain the pressure produced by a

As we can increase the length of the lever or di. column of water as high as the most elevated

minish the diameter of the small piston greatly, part is above them.

the only practical limit to the power of the machine Perhaps the most important application of

is the strength of the large cylinder. An addithis principle is seen in the hydrostatic press, an

tional tap, not showu in the figure, is arranged 50 instrumont which is largely used in the mana

that the water can be allowed to escape from the factures where a very powerful pressure is re

cylinder when it is desired to remove the pressure. quired. The general principle on which it acts

This machine is constantly used by manuis simply this : by means of a piston or plunger,

facturers for many different purposes. Oil is of small diameter, water is forced into a cylin

expressed from seeds by it, goods are com. der in which a large piston works. The latter is

pressed for packing, and many other operations forced ont with a pressure as much greater than

performed. The most remarkable application that exerted on the plunger, as its area is larger.

of it, however, was in the building of the celeIf the large piston have 20 times the diameter

brated tubular bridge over the Menai Straita. of the small one its area will be 400 times as

The longest of the tubes of which this is large, and therefore a pressure of 1 pound will

Fig. 1.

constructed is 472 feet long, and the inside exert a force of 400.

dimensions are about 14 feet wide, and 25 fet The annexed figure (Fig. 2) will give a good idea of the general high. Each weighs about 1,200 tons: they were completely construction of the machine. It varies, however, greatly in finished, and then conveyed on pontoors to the spot, and raised shape and minor details according to the power roquired or the into their place by an hydraulic press, which was the largest special purpose to which it is to be applied. A B represents a ever constructed. Its cylinder was 22 inches internal diameter, lever hinged at B to an upright, and working a solid plunger, 10 inches thick, and 9 feet long, and weighed upwards of 15 D, which is so arranged as only to move in a vertical direction tons. The cross pieces to which the lifting chains were attached This plunger, which is of small dimensions, works water- weighed 13 tons. tight in a small cylinder, C. When it is raised by means The lifting force this press was capable of exerting was estiof the handle, a, water rises from the reservoir, G, into mated at over 2,000 tons. It was erected at the top of the the cylinder through the valve, E, which then closes and towers, and chains were fastened round the tube and attached prevents the water passing

to the cross head of the ram. back again. The piston is now

At each lift the tube was raised forced down, and drives the

about 6 feet, the space underwater through the pipe into

neath was then filled in with the large cylinder, L, and thus communicates the pressure it

masonry, and the chain short

ened for another lift; and in receives from D. A second

this way each tube was raised valve is placed at F, so as to

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to its elevation of 101 feet above keep the water from flowing

high-water mark. back when D is raised again.

As valves are of frequent emThe making of the large cylin

ployment in hydraulic machines

, der, L, requires the greatest

it will be well just to give an care, on account of the immense

explanation of their construcpressure it has to withstand.

tion. The object to be attained When the Great Eastern steamer

by their use is to allow water had to be launched, some

to flow freely along a pipe in presses were used in which the

one direction, but to prevent cylinder was made of iron 7 or 8 inches thick, and yet they

it passing in the other. The

simplest means of acoomplishwere split open by the immense

ing this is by a common clack strain exerted on them. The

valve (Fig. 3, a). This consists piston, K, is made of as large

Fig. 2.

of a plate of metal, hinged at dimensions as practicable, as on this mainly depends the power of the machine. It works water opening. A piece of leather larger than the plate is usually

one edge, and closing over the tight through a collar at I, and it was here that the greatest placed over the upper surface, and the weight of the water practical difficulty was found, for the water oozed through, and presses it against the other surface, thus closing the valve thus the power of the machine was greatly diminished. The more tightly. Another kind of valve is shown at b, and cordifficulty was at last met by making a collar of stout leather, sists of a ball which rises by the pressure of the water, but and so that its section was of the shape of the letter U inverted falls by its own weight, and closes the pipe when the water

This ring is placed in a groove prepared for it, and it is easily tries to pass back. The other variety in common use is the seen that when the water presses on it, it tends to open the spindle valve shown at c. A conical piece of metal is made to fit bend, and thus causes the collar to press more firmly against the into a setting, and confined by a guide rod so as to rise verticalls. piston. The books or other articles to be compressed are laid The best inclination for the sides of the valve is an angle of about upon the flattened top of the piston, and pressed against a 45°, as then there is little danger of its becoming

stack in its framework constructed for the purpose.

setting, and on the other hand it does not waste mach room.

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