Farm. Hem! hem! Well, I an't goin' to give up anything I know; and I sha'n't believe this world turns round till I find I can stand upon my head, for I know the world can't stand without it has something to stand on.

Stu. How do the sun, moon, and stars stay up without their proper foundation?

Farm. How on airth do you think I know? But if the world turns round, what's the reason our minister never said nothing 'bout it? Stu. He'll tell you so now, or he is not fit for a minister.

Farm. You're an impudent scamp! Do you mean to consult me to my face, and a deacon, too?

Stu. If you are offended, I have no more to say.

Farm. Well, I'll make you know better than to conspute me! (Strikes him.)

(Enter MINISTER.)

Min. Hold, deacon! I'm surprised to find you fighting!

Farm. I han't been fighting.

Min. But I saw you fighting.

Farm. Well, he's a villain, and ought to be kicked by every good man, and much more by a deacon!

Min. Why, what has he done?

Farm. Done! why he's done everything. He ought to be hung!
Min. Let us hear what it is?

Farm. Why, he's a blasphemer; he holds to the most conbominable doctrine that ever was under heaven.

Min. But what has he said, Deacon Homespun, that so exasperates you?

Farm. Why, he 'nies the Bible, and says you an't no more fit for a minister than my old one-horned ram.

Min. Wherein has he denied the Bible, pray?

Farm. Why, he says this world is round, and yet folks live on't; and turns over, too; and that an't all-he 'nies the sun's rising and setting; and if a man won't fight when such conbominable doctrine's held up, he can't be a Christian.

ture.

Min. I don't see anything in that, criminal, or contrary to Scrip

Stu. Did I not tell you your minister would say so?

Farm. Well, you're all a pack of blasphemers; you 'nie the Bible, and I won't stay to talk with you! (Leaves, and is heard in the distance, saying:) Haw long here, whoe, git up, whoe hish!

HAV

that wonderful instrument, the Stereoscope, of which we gave some account in the September number of the last volume, we here give a more complete description of its principles and uses. The philosophy of this scientific apparatus is derived from the very simple fact that we have two eyes instead of one, though people did not think that there was anything remarkable in that, until recently.

We are indebted to Professor Wheatstone for the discovery of the stereoscope, which explains the phenomenon of binocular vision, and, although known in the scientific world for nearly fifteen years, has only attracted the attention and excited the curiosity of the public,

from its now general application to photographic productions. Although Professor Wheatstone, soon after the discovery of photography, made use of daguerreotype and talbotype pictures as the most efficient means of producing the illusion of solid representation in his stereoscope, no practical photographers availed themselves of the discovery, and it remained concealed in scientific records, until the subject was again brought into notice, in 1849, by Sir David Brewster. Professor Wheatstone's first stereoscope was composed of two small mirrors placed at an angle of 90°, and each reflecting to one eye one of the two binocular images.

He afterwards constructed a refracting telescope, composed of two prisms of about 8° each, placed between the eye and one picture, and refracting the two images on one intermediate space, where they coalesced. Sir David Brewster recommended a stereoscope somewhat similar, but, instead of two common prisms, supplied with two semi-lenses, acting, at the same time, as refracting prisms and as magnifying glasses, by which the pictures could be considerably enlarged.

This instrument was so constructed that all direct reflection was avoided, which is an indispensable arrangement for the inspection of daguerreotype surfaces; and this contrivance, and the convenient shape of the instrument, has been partly the cause of its great popularity and usefulness. The instrument was called by Sir David Brewster the lenticular stereoscope. Photography alone can produce two images perfectly identical to the two images on the two retina; and if we can place them so that the right perspective is seen only by the right eye, and the left perspective only by the left eye, both in the line of direct vision, we have on each retina the same representation we had from looking at the natural objects.

This is precisely the effect of the stereoscope; therefore, in the stereoscope we have the same sensation of solidity and distance as we have with two eyes. When we look at a solid object, such as a cube or a statue, it is obvious that the right eye sees some parts of the solid which the left eye cannot see, and vice versa. In looking with two eyes, the objects appear solid and separated from each other, because we are unconsciously taught to judge that what is seen by one eye, and not by the other, must be on a receding part of the solid, and hence the idea of solidity in our mind.

When we direct our vision from an object upon an object nearer or more distant, we are obliged to shift the two retine, in order to

cause their axis to correspond with the new angle of vision, and to obtain a single vision. This is done with wonderful rapidity, and we are unconscious of the exertion. This phenomena is beautifully illustrated by two photographic pictures on glass, intended for the stereoscope. M. Claudet, in a lecture at the Society of Arts, showed that these two binocular images were not exactly similar-that each had a different perspective projection. He placed one against the other, and being able to slide them in a grooved frame, there was only one plane of the perspective in each picture which by the superposition could produce a single image; the objects on planes more distant or nearer were distinctly seen double. When the objects on the foreground plane were coinciding, all the objects behind were more and more separated, according to the distance; when the objects of the middle plane were coinciding, all the other objects, before or behind, were separated; and when the more distant objects were coinciding, all the others before were more and more separated as they were nearer and nearer. Therefore, in observing the two binocular pictures in the stereoscope, the eyes are obliged to alter their convergence, in a certain degree, for each distance, and it is to that exertion, and to the duplicity of the images, and their degree of separation both ways, that the mind has the sensation of relief and distance of all the objects represented in the stereoscopic pictures, and the process is exactly the same when looking in the stereoscope on the two binocular pictures, or when looking naturally at the real objects. If the two perspective projections of the daguerreotype images are taken at a greater angle than they are with the eyes for the same apparent size, the optical axes have to alter their convergence in a greater ratio in passing from one point to another; the double images within and beyond the point of vision are more separated than in the natural vision; and from these two exaggerated effects we conclude or feel that the objects are more separated than they are in nature, and that the distance or relief is greater. By magnifying more or less the stereoscopic pictures, we, by the same reason, increase less or more the stereoscopic effect. This is exemplified by looking with a double opera-glass. If we look through the large lens near the eye, we considerably decrease the size of objects; and as the angle of vision remains the same as for natural vision, the eyes have to alter more their convergence, in surveying the various planes, than they would have to do if the objects were really at the distance at which they appear to be. In looking through the eye-pieces of the same opera-glass, we have a

contrary effect, and a very unpleasant one, as we magnify the pictures. If they were seen by the eyes at the distance they appear to be, the angle of the optical axes would be larger than the natural angle; and the exertion in converging from one point to another of the magnified picture is less through the opera-glass than it should be if we were looking at the distance giving the same size of image on the retina. For this reason, double opera-glasses are defective, and produce an incongruous sensation, which is very disagreeable. A single operaglass is far preferable, and gives an idea of greater distance between. the objects, and more relief of their various parts, than a double glass. One of the most remarkable phenomena to which M. Claudet referred, was the singular similarity of effect between squinting outwards and the stereoscope, and squinting inwards and the pseudoscope, when looking at two binocular pictures; for by squinting either way, we can bring the right and left pictures on corresponding parts of the two retinæ. In squinting outwards on a stereoscopic slide, we have, without the stereoscope, the effect of relief and distance; and by squinting inwards, the same effect of intaglio and inverted distances. we have with the pseudoscope, and by squinting vice versâ we have a contrary effect. It is easier to squint inwards, as we do when looking near our nose; and to obtain, by so squinting, the stereoscopic effect in examining the two pictures, we must place the right image under the left eye, and the left image under the right eye. In doing so, we have the most beautiful effect of relief and distance, and more perfect than with the instrument, because the prisms and lenses always cause a certain amount of distortion from spherical and chromatic aberration. We have also another advantage, which is, that on placing the pictures nearer or farther off, we decrease or increase at will the stereoscopic effect, or the relief and distances of the various parts of the picture. M. Claudet showed that two exactly similar pictures, placed in the stereoscope, produced less relief than one of these pictures seen alone with one eye. From this fact he proves why painting can never represent the distance and relief of nature, or stereoscopic vision; that the vision with two eyes of a monocular picture gives a sensation of less relief and distance than with one eye. When the great bridge was building at St. Petersburg, the Czar wished to sce the progress made each day. The superintendent, therefore, had a daguerreotype of the bridge taken every evening. This the Czar looked at through a stereoscope, and thus beheld, not a mere picture of the works, but an image, apparently, as large and solid as the bridge.