1.  An artist can draw an object as he sees it, looking at it only with his right eye.  Then he can draw a second view of the same object as he sees it with his left eye.  It will not be hard to draw a cube or an octahedron in this way; indeed, the first stereoscopic figures were pairs of outlines, right and left, of solid bodies, thus drawn.  But the minute details of a portrait, a group, or a landscape, all so nearly alike to the two eyes, yet not identical in each picture of our natural double view, would defy any human skill to reproduce them exactly.  And just here comes in the photograph to meet the difficulty.  A first picture of an object is taken,—­then the instrument is moved a couple of inches or a little more, the distance between the human eyes, and a second picture is taken.  Better than this, two pictures are taken at once in a double camera.

We were just now stereographed, ourselves, at a moment’s warning, as if we were fugitives from justice.  A skeleton shape, of about a man’s height, its head covered with a black veil, glided across the floor, faced us, lifted its veil, and took a preliminary look.  When we had grown sufficiently rigid in our attitude of studied ease, and got our umbrella into a position of thoughtful carelessness, and put our features with much effort into an unconstrained aspect of cheerfulness tempered with dignity, of manly firmness blended with womanly sensibility, of courtesy, as much as to imply,—­“You honor me, Sir,” toned or sized, as one may say, with something of the self-assertion of a human soul which reflects proudly, “I am superior to all this,”—­when, I say, we were all right, the spectral Mokanna dropped his long veil, and his waiting-slave put a sensitive tablet under its folds.  The veil was then again lifted, and the two great glassy eyes stared at us once more for some thirty seconds.  The veil then dropped again; but in the mean time, the shrouded sorcerer had stolen our double image; we were immortal.  Posterity might thenceforth inspect us, (if not otherwise engaged,) not as a surface only, but in all our dimensions as an undisputed solid man of Boston.

2.  We have now obtained the double-eyed or twin pictures, or STEREOGRAPH, if we may coin a name.  But the pictures are two, and we want to slide them into each other, so to speak, as in natural vision, that we may see them as one.  How shall we make one picture out of two, the corresponding parts of which are separated by a distance of two or three inches?

We can do this in two ways.  First, by squinting as we look at them.  But this is tedious, painful, and to some impossible, or at least very difficult.  We shall find it much easier to look through a couple of glasses that squint for us.  If at the same time they magnify the two pictures, we gain just so much in the distinctness of the picture, which, if the figures on the slide are small, is a great advantage.  One of the easiest ways of accomplishing this double purpose is to cut a convex lens through the middle, grind the curves of the two halves down to straight lines, and join them by their thin edges.  This is a squinting magnifier, and if arranged so that with its right half we see the right picture on the slide, and with its left half the left picture, it squints them both inward so that they run together and form a single picture.