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3. Perta, ót the end of the
isnes Sietiųs, a native of

. acout '603, that by com-
IT. I the other convex, objects

us sorts of telescopes have "S:9. Kown are those of Gregory,

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cum , anime or less inclined. Fig. 321 gives a longitu linal
spetion of it. This telescope, which was invented in 16:50,

s composed of a long brass tube, at one end of which is a
: * seen. 'arge concave mirror, x, of metal, with a circular opening in the

'entre, throuzh which the rays of light pass to the eye-piece.
Hear the other extremity of the tube is a second concave

mirror, y, also metal, something larger than the central aper-
sip-

ture in the other mirror, and with a much smaller radius

of curvature. The axes of these two mirrors coincide with WU, 28 is that of the tube. The centre of curvature of the large one

..; se, Jeing at o, and its focus at ab, the rays, such as s a, enitted

Ilialle, I: by the star or other heavenly bods, are reflected on this It's stun, mirror, and form at a b an inverted and very small image of the 12. like.ighti, budy. Now the distance of the mirrors and their respective

X rays, 2 eurvatures are such, that the place of this image is found > Rissary to between the centre o and the focus f of the small mirror; whence sal : Hace to it follows that the rays, after being reflected a second time on As dit nages the mirror x, form at a'la magnified and in verted image of 2 ),

and, consequently, erect in relation to the object. Finally, we I ne tave just behold this image with an eye-piece, P, which is intended to 1 12.4t for each magnily it anew, and by which we see it at 6" 6".

The objects observed not being always at the same distance, 'desi towards the the focus of the large mirror and consequently that of the

+ uskrozmer small one-may vary its position. Besides, the distance of . --b3 si drepiter, distinct vision not b.ing the same for all eyes, the image 3" **

must be formed at different distances. To suit these variations, in geling insses is not it is necessary to move the small mirror further from, or negrer

1

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to the large one. This is done by means of of a screw, A (fig. clearer. With regard to the magnifying power, it is, as in the 320), which turns a rod that moves the part B, to which the others, the ratio of the principal focal distance of the mirror to small mirror is attached.

that of the eye-piece.
2, Newton's Telescope.- Newton's telescope differs little from Camera Obscura.—The camera obscura, or dark chamber, is
that of Gregory. The concave reflector M, which is at the a room which excludes the light in every part, with the
bottom of the tube (fig. 322), has no opening in the centre, exception of a small aperture, by which the luminous rays
Fig. 322.

enter. Then all external objects whose rays can reach the
opening are painted on the wall opposite, with reduced dimen-
sions, and with their natural colours ; but the images are
inverted,

Porta, a Neapolitan philosopher, discovered, in 1560, the
phenomenon produced by a luminous pencil which penetrates
through a hole into a dark chamber, Shortly after, the same
philosopher observed that if in the opening you fix a bi-convex
lens, and place at its focus a white screen, the image which is
produced gains considerably in brilliancy, in distinctness, in
colour, and is admirably true. These images are bright in
proportion to the size of the lens, and their dimensions aug-

ment with the focal distance. In order to render the camera and the second mirror is plane, with an elliptical contour, and obscura useful in the art of design, various forms are given to inclined at an angle of 45 degrees to the axis of the telescope. it, so as to render it portable, and to rectify the images with This plane mirror is situated between the reflector m and its facility. Fig. 324 represents the sliding dark chamber. It focus, a little nearer to the focus than to the eye-piece o, consists of a rectangular wooden box, into which the luminous placed in the side of the telescope. The result of this arrange- rays r penetrate through the lens B, and form an image on ment is that, after being reflected on the mirror m, and then on the opposite side, o, which ought to be distant from the lens the mirror n, the rays form at ab an inverted and very small B by a length equal to its focal distance. Now the rays image of the heavenly body, between the eye-piece o and its encountering a glass mirror u, with an inclination of 45°, principal focus. This glass produces, then, the effect of a change their direction, and the image is formed on a screen magnifying glass, and gives at a' b' an enlarged, but inverted, of polished glass N. By placing upon this screen a sheet of image of the luminary.

paper, we can take the outline of the image with fidelity. 3. Herschel's Telescope.--The telescope of Herschel, attri. The screen A serves to intercept the light which would illubuted also to Lemaire, is formed of only one concave reflector, mine the image, and prevent the view. The box consists of 1 (fig. 323), and of an eye-piece, o. The reflector is inclined to two parts, which slide by means of a groove into one another, Fig. 323.

80 that the anterior part being drawn out more or less, the
image is formed, after reflection, exactly on the screen n,
whatever be the distance of the object which we wish to
sketch.

Fig. 325 represents another kind of camera obscura, the
dark chamber with a prism. In a brass case, A, there is a

triangular prism, P (fig. 326), which occupies the place at once
M

of a convergent lens and a inirror; for that purpose, one of its
surfaces being plane, the others have a curvature of such a
nature that, by their combined refractions, at the entrance
and exit of the rays, they produce the effect of a convergent
meniscus, c. From this it follows that the rays emitted by

the object A B, after having entered the prism, and experienced
the axis in such a way, that the image of the star we observe is total reflection on the surface cd, form at a b a real image of
formed at a b on the side of the telescope, near the eye-piece o,
which then gives the magnified image a'5'. In this telescope- This being understood, and the tablet B corresponding to the
the rays experiencing but a single reflection—the loss of light focus of the prism contained in the case A, the images of external
is less than in the two preceding ones, and the image is objects are formed on a piece of paper placed upon this tablet.

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his poenale zengin glass

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represented by the verted, real, and di piece R, the rays en in quitting, resp) correspond to ti that the rays, '

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ge mthout the insersion is onder them, se of the light.

Dary i England,

ils soled prispies after 1829, lurmed on a emble by the

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right, and in which the dark and light tints occupied the to 75o, by means of a small lamp supplied with alcohol, samme place as the object.

the mercurial vapours are copiously deposited in the form of In 1829, Niepce communicated his process to Daguerre, small imperceptible drops on those parts which have been who was already known by the invention of the diorama, and strongly illumined, and in the course of a few minutes there sind himself been engaged for several years in similar is formed an amalgamation of silver and mercury, which gives I-searches ; but it was not till after the labour of ten years the white portions of the picture, while the other parts remain that he made, in 1839, the beautiful discovery which has made dark. The image is then visible, and remains when exposed no much noise in the world. Niepce did not live to share the to the sun. However, the plate is still covered, especially in giory, having died three years before.

the shade, with a coat of iodine of silver, which gives to the The process of Daguerre consists of five principal operations. picture a tinge of yellow, mingled with red or violet. This 1 The polishing of the thin brass-plate, coated with silver, on tinge can be made to vanish by washing the plate in a solution which the image is to be formed. 2. Depositing upon this of sulphate of soda. But the image will not resist the slightest plate the sensible coating, that is, the substance susceptible of friction, which proves that the silver and the mercury have impression from the light. 3. The exposure of the plate in a not amalgamated. dark chamber to the action of the light. 4. The exposure

of

There remains, therefore, another operation by which this the plate to the mercurial vapours which cause the image to defect is corrected. The plate is washed in a weak solution of appear. 5. The fixation of the image.

chloride of gold and sulphate of soda. By this operation When the preliminary processes are gone through, the plate the silver is dissolved, while the gold is combined with the is placed in a little portable dark chamber made of wood, mercury and the silver of the plate ; the amalgamation of the which is represented in fig. 329, and which commonly receives mercury and silver, which forms the white of the picture,

then increases the solidity and brightness, by combining with
Fig. 329.

the gold, whence results a remarkable increase of intensity in
the lights of the picture. It is to M. Fizeau that we owe
the employment of chloride of gold, which is the principal
improvement that has been made upon the invention of
Daguerre.
Fig. 330 represents a section of the object-glasses, that is, of

Fig. 330,

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the apparatus which serves to concentrate the light upon the
plate, and to produce the image. It consisted at first of a
single bi-convex achromatic lens, but very soon object-glasses

consisting of two achromatic lenses were adopted. They the name of daguerreotype. This is composed of a fixed part focal distance, and permit an easy adjustment of the focus,

operate more quickly than single object-glasses, have a smaller c, and a moveable part B, and is a real sliding camera obscura. which is accomplished by causing the lens B to approach or In a brass tube a, is the object-glass. It is a convergent achro-recede, it being turned towards the object by means of a rack matic lens, which advances or recedes, by means of a screw and a tooth D. which can be turned with the hand and the button D. The side opposite the object-glass is formed of a polished glass screen fixed in the frame f, which is elevated at will. Matters being thus arranged, in order to obtain a portrait, the person

FEMALE EDUCATION.-N . II. is made to sit four or five yards in front of the object-glass, then we draw the moveable case B, till the image, which is

BY SILVERPEN. produced inverted on the plate of glass, has appeared with distinctness, which happens when the plate is apparently at the HABITS.—So much of a young woman's refinement and imfocus

. It is put at the focus by advancing or withdrawing provement depend on daily habits, as to make it impossible to the object-glass by means of the button D. For portraits, the expect mental or moral progress where these are coarse, low, focus is adapted to the eyes of the person sitting, this part and habitually vulgar. In this respect, I am well aware how of the face being the most central.

many evils the young women of the operative classes have to The focus being found, without displacing the dark chamber, contend against, in respect to poor and often low houses, we elevate the frame e and the glass screen, and put in its place worse companions and neighbours, the want of privacy and the case which contains the plate with iodine. Finally, with good example; but I have seen so much effected by them in drawing the screen which masks the silvered surface, the individual instances, so much which is genteel and womanly, image which is formed on the glass is formed also on the as to assure me that in the majority of cases the duties of plate. It is then that the light produces its mysterious effect, moral refinement and self-respect need but be pointed out to and paints upon the plate an invisible image. The time make them objects

of solicitous acquirement. I have a grand during which the plate should be exposed to the light varies belief in the innate modesty and purity of my sex ; as strong

an assurance that it is through the process of refinement ing, and with the intensity of the light it may be from 3 to 50 women

will yet largely increase the moral bounds of social Seconds. If the exposure be too much prolonged, the picture action; and I do think that any young woman, let surroundwill be white: it will be black if the exposure is too short. ing evils be what they may, can correct the influence of half

When the time has come to arrest the action of the light, of them if she will but reason with herself and say, "I have which long practice alone can enable us to determine, we lower an individual mind and body distinct from that of others; I the screen, and withdraw the case, in which the plate rests in have youth and health and a fresh mind; let me then strive to total darkness. If we observe

the plate at this moment, we rightly use and make the best of these, in spite of my low do not yet perceive any trace of the image. In order to render companions, my coarse mother, my ill-conducted home. it visible, it must be exposed to the action of the vapour of What right have I to be bowed down by these to an equal mercury, by placing it, at an inclination of 45°, in the degradation ? No! let me exercise with discretion these bottom of which, consisting of sheet iron, contains a cavity woman of the onward age, and not the mere slave of the hern part of a wooden box,

prepared for this purpose, the sweet gifts of body and mind, let me show myself a young full of mercury. This being brought to a temperature of 60 habits and manners of those arround me; but superior as far

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mut - 10.2011

** TTUR : 28 of
til en ILLE MILKE I Surde i
nr r ** *23
*** P

& fa : r; 2.1. 2-1m i to bez da

DALILIS. * I * x 120 meter er 2.2 bit fin vous, Ls auber of

T*** L CLmo he puttes ostis 3- the Lun:: a ost. As the Toang woman,

2. kira a las te nise est to be work, ne 95 rumare lhe Ice : le bit of placing *** Fm11ft unEINI:fe of dress as she will

Daudete vibes nestly folded, and 22 E: 2 SİNE *7 nended and decent, -2.25 2T --- her sisw, her barnet ready; and

: a mc water, and a comb and

* PETIT und lack of time for a : * LEI SCT, I Tessing oi the body, at least

28.1. kees De D.TULT rashed, the hair brushed, Si te istide2.c. * beng made an especial point

• 2023 Ene chari2 and healthy looking than *DELEISDECI-an. as I have before said, I utterly

Ei reale eines in matters of this sort. I do not TIN.?.at care, asa ib: Ese of a little camphorated IL she teeth oi the working-girl should not be es

2 ss ihnye of a duchess. It is not nature, but å want of

sa krowanige which makes the difference -- therefore let zit er:1. Before setting off to the mill or shop; the young E: winan siz suid practise the habit of clearing away all things intred she has made use of or worn. It ought to be a matter of con

= 34, I science that no litters, no articles of dress, are left about for ** 7r:t; bet 60 nme poor slave of a mother or sister to clear away, or to be

a reactions, kiesce here and there by children, or the first new-comer;

:!". John or but if articles of dress are neatly folded, and put aside in box -reger,' should or drawer, shoes kept in one place, and the brush and comb 320 d say act which, in a bag, there they will be found wben next wanted, unsoiled

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