« ΠροηγούμενηΣυνέχεια »
of loudness appropriate to each passage. The exercises should | établir son petit marché de vivres la près de cette église, ne be repeated till they can be executed with perfect precision, l'eut aperçue' et ne se fut senties touchée de compassion is 80 as to form a standard for all similar expression, in subse pour la malheureuse enfant. Elle aussi avait des enfants !" quent reading
C'est pourquoi elle s'empressa de prodiguer ses soins à la Exercise in Moderate' Force. ;
petite orpheline.15 Fodora ne savait comment lui té. "An author represents Adam as using the following lan. moigner sa reconnaissance. Elle devint bientôt pour guage. I remember the moment when my existence com
sa seconde mère une aide fort intelligente. Peu à peu, elle menced: it was a moment replete with joy, amazement, and apprità comprendre sa bienfaitricel et put' lui exprimer anxiety. I neither knew what I was, where I was, nor tout ce que son cæur renfermait de reconnaissance et whence I came, I opened my eyes : what an increase of d'amour. sensation! The light, the celestial vault, the verdure of the Cepandant l'armée de Napoléon commença sa retraite ** earth, the transparency of the waters, gave animation to my et la vivandière duti quitter Moscou. Les parents de spirits, and conveyed pleasures which exceed the powers of Fædora existaient-ils encore ? C'est ce que rien n'était renu utterance.''
révéler.'9 Fædora partit donc avec l'armée française. ** Deoamatory' Force.
Qu'on juge de ce qu'un enfant de cet âge eut à endurer “Advance, then, ye future generations ! We bid you wel- pendant une pareille retraite ! Au passage de la Bérézina, come to this pleasant land of the Fathers. We bid you wel. Fædora eut encore le malheur de se trouver séparée de sa come to the healthful skies, and the verdant fields of New bienfaitrice, 21 soit que celle-ci eut péri dans les flots, soit England. We greet your accession to the grest inheritance qu'elle crût la jeune enfant égarée ! Quoiqu'il en soit, which we have enjoyed. We welcome you to the blessings 'orpheline ne la trouva plus, 22° et elle se vit de nouveau of good government and religious liberty. We welcome you délaissée. to the treasures of science and the delights of learning. We welcome you to the transcendant sweets of domestic lite, to
COLLOQUIAL EXERCISE. the happiness of kindred, and parents, and children. We wel. 1. En quelle année Napoléon 12. Que vint faire la rivandière come you to the immeasurable blessings of rational existence, entra-t-il dans Moscou ? près de l'église ? the immortal hope of Christianity, and the light of everlasting 2. Quelle ville l'Einpereur 13. La vitandière eut-elle pitié Truth !"
menaçait-il de là ? • Impassioned' Force.
de la petite malheureuse ?
3. Par quoi Rostopchin fut-il 14. Pourquoi cut-elle pitié de “Shame! shame! that in such a proud moment of life,
le gouverneur ?
16. Fædora parut-elle reconnaisBetween freemen and tyrants had spread through the
5. Où étaient les habitants ? sante? world,
6. Que s'efforçaient-ils d'em. 17. Qu'apprit-elle peu à peu ? That then,--Oh! disgrace upon manhood !-e'en then
18. Que fit l'armée quelque You should falter,--should cling to your pitiful breath,–
7. Qu'arriva-t-il à la petite fille
temps après ? Cower down into beasts, when you might have stood men,
d'un négociant ?
19. Avait-on découvert les pa. And prefer a slave's life, to a glorious death!
8. Que faisait la petite ?
rents de Fædora ? It is strange !-it is dreadful!-Shout, Tyranny, shout,
9. Où étaient son père et sa 20. Que fit-elle alors ?
21. Qu'arriva-t-il au passage
d Through your dungeons and palaces, •Freedom is o'er !- 10. Dans quelle situation If there lingers one spark of her fire, tread it out,
la Bérézina ?
trouva-t-elle à la pointe du 22. L'orpheline retrouva-t-ell And return to your empire of darkness once more."
sa bienfaitrice? 11. Se serait-elle réveillée ?
NOTES AND REFERENCES.- a. L. part ii., $ 23, R. (5).--. FRENCH READING S.--No. X. et là, here and there ; L. S. 98, R. 3.-d. se prit á dorinir, fell
asleep; from prendre ; L. part ii., p. 100.-e. from renir; L. F E D O R A.
part ii., p. 108.-f. L. S. 97, R. 4.-5. L. 9. 97, R. 5.—. from
apprendre; L. part ii., p. 78.-i. from pouvoir ; L. part 3. . SECTION I.
100.--. dut, was compelled to ; from devoir.-k. soit, de it; from
étre.--. from croire ; L. part ü., p. 84. C'ETAIT en mil« huit cent douze ;' Napoléon, à la tête des ses troupes victorieuses dans les plaines de la Moskowa, était entré dans l'antique capitale de l'empire des czars, et, de là menaçait la nouvelle ville fondée par Pierre-le-grand. Poussé par un patriotisme fanatique, le gouverneur de
ANSWERS TO CORRESPONDENTS. Moscou, Rostopchin, prit alors cette résolution qui a porté others want improvement.-J. R. (Port of Monteith). We wish our young
A, W. (Edinburgh): llis solution to Prob. 60 jo Algebra is correct; the un coup si funeste au succès de nos armes, celle d'incendier friend Mary had been more successful,
but hundreds of maturer Terapie bones la ville, dont l'empereur Alexandre lui avait confié la garde. failed in the Four Ball Question.-B. 6.: It is not the privilege of person Nous ne raconterons pas toutes les circonstances de cet academic distinction, compared with the alling of the cranium.-W. More on épouvantable drame. Chassés de leurs demeuresó en feu, (St. Ives): Electrotyping comes under Physics, and illuminating as ander croulant sous les efforts des flammes, c'était un spectacle Chemistry: WARIN (East Dereham): 6. SMITH (Slanchester); 1. D. affreux que de voir tous les habitants mêlés à nos soldats,
We bave received a great number of names to be attached to the Petition forcés de fuir en emportant ce qu'ils pouvaient dérober à la for removing the restrictions of the University of London in reference to violence de l'incendie.
graduates who do not belong to any of the affiliated colleges. The petition
will be presented on the first Wednesday in April, and their pames will be La petite fille d'un négociant, à peine âgée de six ans, se publial, ed immediately a:ter the presentation. trouva perdue dans le tumulte.? Abandonnée, transie de We have received solutions of our Centenary of Algebraic Problems from froid, elle errait ça et làø à travers les rues que le feu épar- solutions a place in our pages very soon indeed.
a great many of our Correspondents, and we shall gire their names and gnait encore. Son père et sa mère avaient disparu, et
pea solved Geometrical Problems in " Cause's Euclid," and others to be found ainsi tout entière ; et quand le jour commença à poindre, We also propose a Quadratic Equation to be solred by the rules of simple Fædora, exténuée de fatigue et de faim, s'affaissa devant la equations or of pure equations, as some of our students seem to be aco
quainted with more than we gave them credit lor, in the lateresting science porte d'une église 10 et se prit« à dormir. stans doute elle ne se serait plus réveillée," la mort serait diferentes of their aquares, and the sum of their oquarco equal to like difere
PROBLEM.-Required two numbers such that their product is equal to the yenue la surprendre, si une vivandière, qui par harsard vinte | ence of their cubicos
1st. The intensity of radiant caloric is proportional to the ON PHYSICS, OR NATURAL PHILOSOPHY.
temperature of its source.
2nd. This intensity is in the inverse ratio of the square of
the distance. No. XXXI.
3rd. The intensity of the calorific rays is less in proportion (Continued from page 55.)
as their direction is more oblique in relation to the radiating
surface from which they are emitted. RADIATION OF CALORIC.
The first law is proved by presenting one of the bulbs of a
differential thermometer to variable sources of hea', as a cubic Propagation of Caloric in a Homogeneous Medium. When a vessel made of tin and filled successively with water at the body is placed in a medium of which the temperature is temperatures of 309, 20°, and 10°, on the Centigrade thermohigher or lower than its own, it is always observed that the meier. In this case it is found that, at the same distance, the temperature of the body rises or falls by degrees, until it has thermometer indicates temperatures which are in the same reached that of the medium by which it is surrounded ; 1 ratio as those just mentioned, viz., as the numbers 6, 4, and 2 whence it is inferred that the body has gained or lost a certain are to each other. quantity of heat-a quantity which it has taken from the In order to prove the second law by experiment, a differential medium, or which it has given to the same. Heat, therefore, thermometer is placed at a certain distance from a constant is transmitted from one body to another, through space, in source of heat, and then at a double distance, and we find that the same manner as light. The caloric which is thus pro- the thermometer in the second position indicates a temperapagated at a distance is called radiant caloric ; and a ray of heat, ture four times less than in the former position. At a triple or a calorific ray, is the straight line which caloric takes in its distance it indicates a temperature nine times less. propagation.
This second law is also proved by referring to the geometrical Heat is also transmitted through the very mass of bodies; theorem that the surface of a sphere increases as the square of it is then an actual interior radiation from particle to particle iis radius. Thus, if we conceive a hollow sphere of any radius, which is produced, and which we recognise under the name at the centre of which is placed a constant source of heat, of conductibility.
every unit of the interior surface receives a fixed quantity of Laws of Radiation. The radiation of caloric is presented to heat. Now, if the radius of the sphere be doubled, its surface, us under the three following laws :
according to the theorem just cited, would be quadrupled. 1st. Radiation takes place in all directions around heated The interior surface would therefore contain four times more bodies. Thus, if we place a thermometer in different positions units of surface; and as the quantity of heat emitted from the around a heated body, it will indicate in all of them an eleva- centre remains the same, every unit would necessarily receive tion ci temperature.
four times less of it. 2nd. In a homogeneous medium radiation takes place in The third law can be proved by the following experiment: straight lines. For if we interpose a screen on the straight Fix horizontally on a support, a tube made of pasteboard line which joins the source of heat and the thermometer, the blackened in the interior, and about twenty inches long. At one latter will cease to be influenced by that gource. But in of its extremities place the bulb of a differential thermometer, passing from one medium into another, as from air into glass, and at the other a cubic vessel made of tin, filled with boiling the calorific rays, like the luminous rays, are generally de- water, and arranged so that one of its faces may be perpenflectedma phenomenon which is denominated refraction, and of dicular to the axis of the tube. The calorific rays which reach which we shall see the laws under the head of “Optics,” the bulb of the thermometer being necessarily directed in a these laws being the same both for light and for heat. straight line parallel to this axis, it is evident that they are
3rd. Radiant caloric is propagated in a vacuum as well as in perpendicular to the face of the cube. When the thermoair
. This is proved by placing a small thermome:er in an meier becomes stationary, note the number of degrees which exhausted receiver. For if we bring a heated body near to it, it indicates ; then, without altering the distance of the parts we perceive the thermometer rising at its approach, a pheno- of the apparatus, turn the cube slightly in such a manner that menon which can only be ascribed to the radiation of heat in the face, which was perpendicular to'lhe axis, may now be a Facuum; for we shall soon see that glass does not conduct more or less inclined to it. In this new position the rays of heat sufficiently well to propagate it through the sides of the heat, which always take that direction in the tube which is receiver and the stem of the thermometer.
parallel to the axis, are now inclined to the face of the tube, 4th. The velocity of the propagation of caloric has not been at the same time the portion of this face from which the radi. Jet ascertained with sufficient accuracy. It was generally ation proceeds to the thermometer-bulb is increased. In the considered, till very lately, that heat travelled with the same, first case, in fact, this portion of the face was equal to the or nearly the game, velocity as light. Modern experiments interior section of the tube parallel to the axis; in the second have led to the conclusion that the rate at which heat is case it is equal to an oblique section of that tube. The radiant radiated from the sun is only about four-fifths of the rate at surface is thus increased, and the tube is trarersed by a greater which light is propagated from the same luminary, or about number of calorific rays. Now, the differential thermometer 160,000 miles per second. Von Wrede measured the velocity continues to indicate the same temperature; therefore the of heat in the following manner : he considered that if the oblique rays are less intense than the perpendicular rays. heas and light in the sun's rays possessed unequal velocities, The doctrine of forces shows that the intensity of the rays is that the aberrations of these rays would also be unequal; and proportional to the sines of the angle which their direction that consequently the image of the sun, formed in a telescope by makes with the radiant surface. the calorific rays and by the luminous rays, would not coincide, Moveable Equilibrium of Temperature.—Two hypotheses have but would be inclined to each other in a direction parallel to the been proposed as the principle of radiation ; in the first it is ecliptic One result of this would be, that the temperatures on supposed that, when two bodies of unequal temperature are the eastern and western edges of the image of the sun would near each other, radiation takes place only from the warmer net
be equal. By means of a thermo-electric calorimeter placed body to the other which is cooler than it, the latter emitting in the telescope, it was found that the temperature of the nothing towards the former, until the temperature of the edge, and
that consequently the velocity of the calorific rays that of the other body, and then all radiation ceases. This was less than that of the luminous rays. The mean of a great hypothesis has been replaced by the second, which is generally number of observations gave the proportion above mentioned; adopted in the present state of our knowledge, and is due to but this result requires confirmation by other experiments. M. Prevost of Geneva, viz., that all bodies, whatever be their
Variation of the Intensity of Radiant Calorie.-Three causes temperature, are constant's emitting caloric in all directions. modify the intensity of radiant caloric; the temperature of the Then, a loss of temperature, that is a cooling, takes place in source of heat, its distance, and the obliquity of the calorific those bodies whose temperature is the highest, because that mays in relation to the surface which emits them. Thus, the the rays which they emit have a greater intensity than those three following laws on the intensity of radiant caloric are which they receive. On the contrary, a gain of temperature,
that is a heating, takes place in those bodies whose tempera
ture is lowest. Consequently there is a period when the 1st. The angle of reflection is equal to the angle of inci.
TID air. In both cases the velocity of cooling or heating, that is, the quantity of heat lost or gained in a second, is proportional to the difference of temperature. Newton has stated the following law on the cooling or hearing of bodies:--The quantity of heat which a body loses or gais per second, is proportional to the difference between its teroperature and that of the surrounding medium. MM, Dulong and Petit have shown that this law is not general, as Newton supposed, and that it is only applicable to difference of temperatures which do not Reflection of Concave Mirrors,-Spherical or parabolic surfaces exceed 15° or 209 Centigrade. Beyond this the quantity of made in metal or in glass, and constructed so as to concentrate heat lost or gained is greater than the law indicates. The in the same point luminous or calorific rays, are called concare following are consequences of Newton's law:
mirrors or reflectors. Let us consider the case of spherical 1st. When a body is exposed to a constant source of heat, mirrors. In fig. 168 are represented two of these mirrors, and its temperature is not raised to an indefinite extent, for the in fig. 167 a vertical and focal section of one of them. The quantity of heat which it receives in equal times is always centre, c, (fig. 167) of the sphere to which the mirror belongs the same, whilst that which it loses increases with the excess (that is, of which it would form a part), is called the centre of of its temperature above that of the surrounding air. A period curvature; the point a, the middle of the reflector, is the centre will, therefore, arrive when the quantity of heat emitted is of figure; and the straight line, A B, drawn through these two equal to that which is absorbed, and the temperature is then points, is the principal axis of the mirror. 8 ationary.
In order to apply to spherical mirrors the laws of reflection 2nd, The law of Newton, applied to the differential thermo- which belong to plane surfaces, they are considered as formed meier, shows that the indications of this instrument are of an infinity of plane surfaces each infinitely small - a hypoproportional to the quantities of heat which it receives. For thesis which admits of our demonstrating geometrically that instance, let one of the bulbs of a differential thermometer the normals to these small surfaces all meet in the centre of receive rays of heat emitted from a constant source; the curvature. Thus, on the axis A B of the mirror mx, let a instrument will at first indicate increasing temperatures, then source of heat be supposed to be situated at a distance suffiit will become stationary; and this will be indicated by the ciently great, so that the rays EK, PI, etc., which emanate fixed position which the index assumes. At this instant the from it, may be considered as parallel to AB and to each other. quantity of heat which the bulb receives is equal to the quan- According to this hypothesis, that the mirror is formed of an tity which it emits. But the quantity is, according to the law infinite number of plane surfaces each infinitely small, the ray of Newton, proportional to the excess of the temperature of Ek is reflected from the element « as from a plane mirror; the bulb above that of the medium, that is, to the number of whence, the straight line o x being normal to this element, the degrees marked on the thermometer. Therefore, the tempe- ray takes a direction, K F, such that the angle ckp is equal to rature indicated by the di sential thermometer is also pro- the angle cke. The other rays, P, 1, etc., being reflected in portional to the quantiiy 1. valoric which it receives.
the same manner, all these rays, after reflection, sensibly meet
strated in "Optics." There is, therefore, at the point pa THE REFLECTION, EMISSION AND ABSORPTION OF meeting of the calorific rays, and consequently a greater eleva. CALORIC.
tion of temperature there than at any other point. Whence
the name focus (Latin, a fire) has been given to this point, Laws of Reflection. When the calorific rays fall on the The distance FA of the focus from the mirror is called the focal surface of a body, they are generally divided into two sets ; distance. the one set penetrates the mass of the body, the other set
accompanying figure, the caloric is propagated along the rises as if it were driven from the surface in the manner of an lines e KF, LDP, etc., in the direction of the arrows; but elastic ball, a phenomenon which is described by saying that conversely, if the heated body is placed at P, the caloric is it is reflected. Thus, if mn, in fig. 166, represents a plane propagated along the lines FkE, FDL, etc., so that the rays reflecting surface; AB a ray of leat, called the incident ray; emitted from the focus become, after reflection, parallel to BD a straight line perpendicular to the surface mn, called the each other and to the axis AB; whence it follows that the normal to that surface; and B C the ray of heat thrown off the heat which is transmitted does not lose its intensity. surface, called the reflected ray; then the angle A B D is called Conjugate Mirrors.--The following experiment, made nearly the angle of incidence, and the angle
DBO is called the angle of at the same time by Scheele in Sweden, and by Pietet af reflection. Now, as the reflection of caloric takes place in the Geneva, proves
the existence of the foci, and also the laws of same manner as the reflection of light, the following laws the reflection of caloric. Two reflectors of the
same size were hold good in the former as well as in the latter :
arranged about four or five yards apart from each other, i
such a manner that their axes coincided. At A, fig. 168, the ice, the surrounding air being at 12° or 150 Centigrade, and focus of one of them, is placed a small iron-wire basket of in the focus of the other a differential thermometer, this red-hot coals, and in the focus of the other, at B, is placed an instrument will indicate a reduction of several degrees of inflammable body, as a piece of amadou or tinder. Then, the temperature. This phenomenon seems, at first sight, to be rays emitted from the source of heat, at A, are reflected, the the effect of the frigorific rays emitted from the ice; but this first time, from the mirror at whose focus this source is placed; apparent reflection of cold, as it is called, is explained on the and taking, in consequence of this reflection, a direction principles, above stated, concerning the equilibrium of tempeparallel to the axis, these rays are reflected the second time rature which bodies always tend to establish between each from the other mirror and meet at its focus B. This is proved other. There is still an exchange of caloriç, just as in the at once by the result; for the piece of tinder placed at this experiment of the setting of the tinder on fire, only the parts point is set on fire: but either above or below the focus this of the phenomenon are changed; and in ihis case it is the phenomenon does not take place.
thermometer which is the warm body. . As the rays which it This experiment proves that heat and light are reflected emits are stronger than those emitted by the ice, there is no according to the same laws. Moreover, if we place at the compensation between the heat which it gives and the heat focus a a lighted candle, and at the focus B a piece of ground which it receives; whence iis reduction of temperature. It glass, there will be seen in the latter a luminous focus exactly is on the same principle that we explain the cold which is felt in the place where the tinder was set on fire. This shows when we are near walls in plaster, stone, or marble; and, in that a luminous focus and a calorific focus are formed at the general, when we are close to any body whose temperature is same point; the reflection takes place, therefore, in both lower than our own. cases, according to the same laws.
Reflecting Power. The property which bodies possess of
It is owing to the high temperature which can be obtained | reflecting a greater or less portion of the heat which falls upon
The source of heat is a hollow cube, m, filled with boiling eight inches long and six inches broad. They could be turned water. On the axis of a spherical reflector, between the focus independently of each other in any direction, so that the and the mirror, is fixed a plate, 4, formed of the substance reflected rays could be made to meet in the some point. With whose reflecting power is required.
With this arrangement, 128 pieces of glass and a burning summer's sun, Buffon set the rays emitted from the source and reflected the first time, fino aire & tarred plank of wood at the distance of about 220 fall on the plate a, and are thence reflected a second time,
forming their focus between the plate and the mirror, in á Reflection in a Vacuum.--Caloric is reflected in a vacuum as point where the bulb of a thermoscope is placed. Now, the Hell as in air. This was proved by Sir Humphrey Davy by mirror and the thermoscope remaining unchanged, and the the following experiment. Under the exhausted receiver of water in the cube being kept always at 100° Centigrade, the in dir-pump, two small mirrors were placed facing each other; temperature indicated by the thermoscope varies with the
nature of the substance of which the plate A is formed when and in the focus of the other a source of electric heat, consist- subjected to the experiment; whence we deduce not the ing of platinum wire, which was rendered incandescent by absolute reflecting power of a body, but the ratio of this making the current of a voltaic pile pass through it; the power to that of another body, assumed as a standard of com. thermometer rose immediately, by several degrees
, on the parison ; that is, in conformity
with what has been said on application of the current- a phenomenon which
was only due the application of Newton's law, the temperatures indicated to the reflected caloric, for the thermometer would have ex. by this instrument are proportional to the quantities of heat perienced no elevation of temperature had it not been exactly which it receives. Thus, it a plate of glass causes the differenin the focus of the second mirror.
tial thermometer to rise 1°, and a plate of lead causes it to rise Apparent Reflection of Cold. If two reflectors are arranged 6°, we conclude that the heat reflected by lead is six times facing each other, as represented in fig. 168, and instead of greater than that reflected by glass ; for the quantity of heat red-hot coals we place in the focus of one of them a piece of emitted by the source is the same, the concave mirror reflects
the same portion of it to each, and the difference can only
Re:ative Reflecting Powero. depend on the reflecting power of the plates at A. According Glass
10 to this mode of experimenting, and by representing the
Glas3 wetted with oil
5 reflecting power of brass by 100, when taken as a standard of Glass wetted with water ...
0 comparison, Leslie constructed the following table of the Lamp-black
0 relative reflecting powers of different substances :
M. Melloni has also investigated the reflecting powers of substances.
Relative Reflecting Powers. bodies, and it follows from his experiments and those of Leslie, Brass
that the reflecting power of metals is much greater than that Silver
of other bodies, as shown in the preceding table. M. dielloni Block Tin
80 has proved, by means of his apparatus, that of all the metals, Steel
70 mercury has the greatest reflecting power. There are causes, Lead
however, which modify the reflecting power of the same China Ink
LESSONS IN CHEMISTRY.-No. XXX.
by proposing the question for solution : what are the metals
capable of being exposed to a fusing temperature, under con. As a preliminary to our cupelling operations, we shall require Four or perhaps five might possibly be enumerated; but
ditions favourable to oxidation, without oxidation ensuing? a small piece of lead, say a shot, a piece of wood charcoal, and practically there are only two namely, gold and silver. They of charcoal a slight depression, and into this deposit the lead; may be kept in fusion for an indefinite period, under the cirwhich being done, direct upon the lead the continuous outside halo of a blowpipe-flame, as represented by the accom
Tig. 27, panying sketch, fig. 27.
The metal will fuse at first; then, becoming converted into oxide, the surface of the charcoal, to the extent perhaps of a quarter of an inch all round, will assume a yellowish or reddish uspect, due to the presence of oxide of lead. By continuing sufliciently long the blowpipe operation, all the metal admits of being oxidised. Careful attention of the phenomena which present themselves during the operation of fusion, will more. over show that the oxide of lead thus produced is remarkably fusible; will show that the oxide becomes, in point of fact, quite liquid, soaking into the substance of the charcoal, where it may be observed on breaking the latter across. It follows, therefore, that if instead of charcoal we had employed some other material of greater absorbent power, all the oxide might have been removed ; filtered away, thus to speak, so soon as formed. We are beginning to see the principle upon which depends the cupelling operation. Let the student now assume a general case. Let it be assumed, I say, that instead of lead aline exposed to an oxidising heat, we had to deal with an alloy of lead and some other metal, the latter being capable of fusion but not oxidation; then it follows theoretically, that separation of the two metals might be effected by taking advantage of the chemical peculiarity just mentioned. In other words, while all the lead should be susceptible of oxidation and absorption, all of the second metal remained behind. Let us now proceed one step further in our theoretical inyestigation