object, suppose a grain of sand, will apparently be eight times larger in diameter, 64 times in surface, and 519 times larger in bulk! This simple microscope is nothing inore than a small hole pricked with a fine needle through a piece of blacked card, The hole, by limiting the number of rays from the object, will enable you ti see the object as above, and prove that the size is no tha angle, or inversely as the distance. Every ohjeet the Jength or breadth, is, in size, in the inverse proportion of its distance because the angle, which its size subtends to the eye, is of a size inversely proportioned to the die tance. Thus, a man at 100 yards distant, is but half the apparent height that he is at the distance of 50 yards, ned only a tenth of his size at ten yards distance. He is magnified, therefore, ten times, by any contrivance which enables us to view him under the same angle at 100 yards distant as we should see him with the naked eye at 10 yards.

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581 The object, then, of all arrangements of glasses, or lens, in microscopes and teles. copes, is first to produce an image of the ol ject, and then to dispose of the rays proceeding or diverging from the image, in such manner, as that it may produce distinct vision in the eye.

The sole use of the object-glass is so to dis pose the rays anew, as that they may produce vision by the approximation of an eye glass: and the magnifying power will depend on the closeness with which the eye glass enables the eye to see the image produced by the objec glass; or, on the convexity of the eye glass.

Or, in other words, the magnifying power will be in the ratio of the focal distance of the object glass to that of the eye-gluss.

Obs. 1.-If a tree, at the distance of 400 vardı, sob. tend an angle of one degree to the naked eye, and ma

image of it is produced by the object-glass of a telescope, and I am enabled by the convexity of an eye-glass to view that image so closely, as that the visual angle is inereased to 40 degrees, the effect is the same as if I had advanced within 10 yards of the tree, when its angle would, to the naked eye, have been increased to 40 degrees. The tree is consequently magnified by the eyeglass 40 times in heighth and breadth.

2. In a microscrope, as the object itself can be brought so near, as to serve the purpose of the image in the telescope, the single microscope is but one lens, but the compound microscope is an arrangement of eyeglasses; which, in some of them, enables the eye to view the image within the 50th part of an inch; thereby enJarging the object in comparison with the natural vision, at six inches distance, 360 times in length and breadth, or 9,000 times in surface.

THE TELESCOPE.

AD is the Object-Glass, or glass nearest the object.
EY is the eye-glass.

K is the eye of the observer.

OB is the object or scene to be viewed.

OCB is the angle under which the remote object is seen by the naked eye.

ICM is the angle of the optical image produced by the object-glass, and is equal to the angle OC B, being produced by the crossing of the same lines.

The glass E Y enables the eye to see the image IM under the angle E K Y, which is the same as E P Y.

Those angles are, however, in the inverse ratio of the distances E P and P G; or, in other words, as the focal distances of the object and eye-glasses, and such, therefore, is the power of the telescope generally.

In such a glass, the image will be reversed to the eye, but, by adding two other eye-glasses, it is set straight again. In Gallileos, however, only one eye-glass is need

ful. In viewing the heavenly bodies, the reversal is of no consequence.

582. As the image is reversed by a single lens.. owing to the crossing of the rays in the centre of the lens, the magnified image is reversed when viewed with one eye-glass; two other glasses are therefore added; one for the purpose of restoring the image to its natural position; and the other for the purpose of viewing it as at first.

The lens within the eye, reverses objects;"but the mind contemplates the top of the optic nerve, as corresponding with the bottom of the object; and the mental effect, is the result of habit, or of learning to see in infancy, or after the eyes have been couched in manhood.

583. Telescopes are refractors, when the effect is produced solely by refraction through transparent lenses; or reflectors, when the image is produced by the converging rays of a concave mirror; but the principle of the magnifying power is the same in all.

They are called Gallileos when the eye-glass is concave, after Gallileo, the inventor of tele. scopes, who made all his discoveries in astronomy by a small telescope, which magnified but 12 times; whereas Herschel's great telescope magnifies 6,000 times!

684. Of course, without light, the world would be involved in total darkness; and without the mechanism of eyes, and optic nerves to convey the varied sensations of light to the brain, a the beauties of nature derived from its diversity

of colouring, all the interesting relations of day and night, and half the pleasures of existence, would be totally lost.

The cause of the various colours which adorn the creation is, of course, an object of interesting inquiry; this discovery was the greatest of those made by Newton.

The beams of light had been in vain display'd,
Had not the eye been fit for vision made

In vain, the Author had the eye prepar'd,
With so much skill, had not the light appear'd.

BLACKMORE.

585. Every one observes the beautiful colours produced by the pendent drops of cut-glass hanging to lustres and chandeliers, whether de rived from candle-light or sunshine.

It is observed too, that drops of rain are coloured in like manner, when the sun shines upon them; and the regular form of the colours in the rainbow, led Newton to conclude, that these colours, as well as colours in general, were produced by some property in rays of light.

586. Newton made a beam of sunshine pass through a hole in a window-shutter, and fall on a glass prism or wedge, so as to be refracted out of its course towards the ground, and thrown upwards on the opposite wall.

He then found, that the circular beam of light was rendered oblong, and regularly coloured; that the uppermost part, or the rays most refracted, were violet, their next division indigo, the next blue, then green, yellow, orange, and, at bottom, red, being the seven colours of the rainbow.

Of parent-colours, first, the flaming red
Sprung vivid forth; the tawny orange, next ;'
And next, delicious yellow; by whose side
Fell the kind beams of all-refreshing green
Then the pure blue, that swells autumnal skies,
Ethereal play'd; and then, of sadder hue
Emerg'd the deepen'd indigo, as when
The heavy skirted evening droops with frost 4
While the last gleamings of refracted light
Dy'd, in the fainting vialet, away.

BLACKMORS

E represents the shutter of a room,
Da hole in the shutter,

S rays of light proceeding from the sun passing through the hole, and falling on the glass prism B'A C; on juzeling which at B C, instead of going straight on, it is refracted, and leaves the prism at A C,

Tis its figure on the opposite wall, spread from a eircle to an oblong, and presenting the colours of the refracted rays in succession as marked,

587. A beam of white light is, therefore, found to consist of rays of all the colours; and it is evident, that the various colours of all the bodies in nature, depend solely on the power of the surfaces to absorb some rays, and reflect others.