Ko. XIX.] APPENDIX. 279 



No. XIX. 



ON BINOCULAR PERSPECTIVE. From the Second Edition of 

 Alfebd Smee's book, ' The Eye in Health and Disease,' and from 

 other notes, &c. 1854. 



"In the last edition of this book, I stated that we know that it is 

 impossible for any painter to delineate a picture in the manner in which 

 we see it with both eyes, because two eyes give us a view of three sides of 

 a cube, and he can paint but two. I conceive it possible, that for objects 

 at moderate distances, painters may, in some cases, take a certain liberty 

 with perspective and depict the two perspectives ; but it certainly cannot 

 be attempted with near objects. 



" Notwithstanding the assertion of the impossibility of delineating a 

 picture as seen with two eyes, which was the correct opiaion of the timCj 

 certain abstract considerations, with which I need not trouble my readers, 

 induced me to believe that such a delineation was more practicable than 

 at first sight was supposed ; and after much thought and studious expeii- 

 ment, I trust that I am enabled to submit the laws by which painters may 

 represent, to a great extent, objects as seen with both eyes, and conse- 

 quently in all their natural beauty. 



" In studying the phenomena of binocular perspective, it must be 

 remembered that the two eyes, being placed at two inches and a half apart, 

 give a different perspective view ; and, as in nature the eyes are directed 

 to the same point, it follows that the same part of the same object must be 

 the same point of eight for the two perspectives. 



"The picture in a binocular perspective drawing really consists of 

 two drawings overlapping each other, the point of sight in both being 

 the same. By this overlapping, lights and shades, tones and the effect 

 of breadth, are produced, such as the eyes really observe in nature. 



"The following may be regarded as the leading rules or laws of 

 binocular perspective, which may be useful to the painter as a guide in 

 the production of the drawing, or as a test for the detection of en-or when 

 it has been made. Much judgment and skill are no doubt requisite for 

 the painter so to construct his picture that the effect of solidity may be 

 suggested to the mind rather than hardly delineated ; and, as far as I can 

 judge, from the observation of paintings of some of our great artists, they 

 have, as an effort of genius, really depicted objects as seen with two eyes." 



For example, he found that " Paul Vei'onese most skilfully obtains the 

 effect of solidity by the suggestion of a line more or less broken to conceal 

 his artifice, outside the limbs of the figures which he has represented." My 

 father never entered a picture-gallery without testing the pictures by his 

 laws of binocular perspective ; and when he was at Rome in 1868, he made 

 some interesting notes of the pictures in the Vatican, in which he found that 

 the great masters produced in somewhat different manners the principles 

 of binocular perspective, although the laws for the same were unknown to 

 them. Thus, in Baracoi's pictures, there is " an indefiniteness of edge ;" 

 in Guide's there is " a gradation of tint — an undefined half-tone;" in 

 Oorreggio's, "the edge is double;" in Paul Veronese's, "the second line is 

 half pencilled in ;" in Andrea Sacchi's, " half-tone outside edge ;" in Bar- 



