Sir David Brewster on a Binocular Camera, fyc. 29 



fix, at the height of his eyes, a metallic plate with two small 

 holes in it, whose distance is equal to that of his eyes, and he 

 would then draw the statue as seen through the holes by each 

 eye. These pictures, however, whatever be his skill, would not 

 be such as to reproduce the statue by their union. An accu- 

 racy, almost mathematical, is necessary for this purpose ; and 

 this can only be obtained from pictures executed by the processes 

 of the Daguerreotype and Talbotype. In order to do this with 

 the requisite nicety, we must construct a binocular camera, 

 which will take the pictures simultaneously and of the same 

 size ; that is, a camera with two lenses of the same aperture and 

 focal length, placed at the same distance as the two eyes. As it 

 is impossible to grind and polish two lenses, whether single or 

 achromatic, of exactly the same focal lengths, even if we had the 

 vexy same glass for each, I propose to bisect the lenses, and con- 

 struct the instrument with semilenses, which will give us pic- 

 tures of precisely the same size and definition. These lenses 

 should be placed with their diameters of bisection parallel to one 

 another, and at the distance of 2| inches, which is the average 

 distance of the eyes in man ; and, when fixed in a box of suffi- 

 cient size, will form a binocular camera, which will give us, at 

 the same instant, with the same lights and shadows, and of the 

 same size, such dissimilar pictures of statues, buildings, land- 

 scapes, and living objects, as will reproduce them in relief in the 

 stereoscope. 



It is obvious, however, from observations previously made, that 

 even this camera will only be applicable to statues of small 

 dimensions, which have a high enough relief, from the eyes 

 seeing, as it were, well around them, to give sufficiently dissi- 

 milar pictures for the stereoscope. As we cannot increase the 

 distance between our eyes, and thus obtain a higher degree of 

 relief for bodies of large dimensions, how are we to proceed in 

 order to obtain drawings of such bodies of the requisite relief? 



Let us suppose the statue to be colossal, and ten feet wide, 

 and that dissimilar drawings of it about three inches high are 

 required for the stereoscope. These drawings are forty times 

 narrower than the statue, and must be taken at such a distance 

 that, with a binocular camera having its semilenses 2| inches 

 distant, the relief would be almost evanescent. We must, there- 

 fore, suppose the statue to be reduced n times, and place the 

 semilenses of the binocular camera at the distance nx2{ inches. 

 If ra=10, the statue will be reduced to y{j, or to 1 foot, and 

 n x 2\, or the distance of the semilenses will be 25 inches. If 

 the semilenses are placed at this distance, and dissimilar pictures 

 of the colossal statue taken, they will reproduce by their union 

 a statue one lout high, which will have exactly the same appear- 



