Sir David Brewster on a Binocular Camera, fyc. 27 



Wheatstone had previously applied his stereoscope to the union 

 of dissimilar drawings of small statues, taken hy the Daguerre- 

 otype and Talbotype processes ; and in an essay on Photography, 

 lately published*, I have mentioned its application to statues of 

 all sizes, and even to living figures, by means of a binocular 

 camera. The object of the present paper is to describe the 

 binocular camera, and to explain the principles and methods 

 by which this application of the stereoscope is to be carried into 

 effect. 



The vision of bodies of three dimensions, or of groups of such 

 bodies combined, has never been sufficiently studied either by 

 artists or philosophers. Leonardo da Vinci, who united in a re- 

 markable degree a knowledge of art and science, has, in a passage 

 of his Trattato della Pittura, quoted by Dr. Smith of Cambridgef, 

 made a brief reference to it insofar as binocular vision is con- 

 cerned ; but till the publication of Professor Wheatstone' s in- 

 teresting memoir " On some remarkable and hitherto unobserved 

 Phenomena of Binocular Vision J," the subject had excited no 

 attention. 



In order to understand the subject, we shall first consider the 

 vision with one eye of objects of three dimensions, when of dif- 

 ferent magnitudes and placed at different distances. When we 

 thus view a building or a full-length or colossal statue at a short 

 distance, a picture of all its visible parts is formed on the retina. 

 If we view it at a greater distance, certain parts cease to be seen, 

 and other parts come into view ; and this change on the picture 

 will go on, but will become less and less perceptible as we retire 

 from the original. If we now look at the building or statue 

 from a distance through a telescope, so as to present it to us 

 with the same distinctness, and of the same apparent magnitude 

 as we saw it at our first position, the two pictures wdl be essen- 

 tially different ; all the parts which ceased to be visible as we 

 retired will still be invisible, and all the parts which were not 

 seen at our first position, but became visible by retiring, will be 

 seen in the telescopic picture. Hence the parts seen by the near 

 eye, and not by the distant telescope, will be those towards the 

 middle of the building or statue, whose surfaces converge, as it 

 were, towards the eye ; while those seen by the telescope, and 

 not by the eye, will be the external parts of the object whose 

 surfaces converge less, or approach to parallelism. It will depend 

 on the nature of the building or the statue which of these pic- 

 tures gives us the most favourable representation of it. 



* North British Review, vol. vii. p. 502, August 1847- 

 t Complete System of Optics, vol. ii. Remarks, p. 41. § 244. 

 J Phil, Trans., 1838, p. 3/1 ; see also Edinburgh Transactions, vol. xv. 

 pp. 31!* and 663. 



