Position of the eyes in sleepiness. 168 
divergence was very small, and therefore, as might have been 
expected, in proportion as the distance —— iGeeoicnl points 
of the pictures was greater, the distance from the eyes at which 
the pictures must be e placed must also be cael For in- 
stance: when the distance betw een identical points was three 
inches the pictures were held at arm’s length; when the aarp 
was six inches the pictures were p laced on the other side of the 
room. It would be curious to enquire, at what distance sud of 
what szze, siindacinns to the laws of vision, the stereoscopic image 
ought to seem in this case. For while one condition of single 
vision, the absolutely necessary one, viz: that the retinal im- 
ages shall occupy corresponding points on the two retine, is 
satisfied ; another condition. which if not —— ities 
is present in every act of single vision except this 
condition which determines the apparent place te size of the 
object or stereoscopic image—viz: the meeting of the two visual 
lines, ts uot satisfied. In all cases of single vision, whether of 
natural objects or by stereoscopic combinations, the object or 
stereoscopic image is seen at the intersection of the visual lines, 
which is therefore called the point of sight. But in this case 
there is no point of sight at all—the visual lines do not meet 
at all noua bokaed the head. 
In one of my papers on binocular vision* I gave a new 
method of representing the position of double images ; a method 
which, however, represents equally well the position of images 
seen single by stereoscopic combination. The facts which I 
have just presented may be perfectly a ee by ry 
method, but cannot by any other. Let Rand L fig. 1) rep 
sent the position of the eyes in sleepiness, and . the Pee ect 
* This Jour., Ser. ITI, vol. i, p. 33. 
