162 J. LeConte on Binocular Vision. 
both look at the root of the nose. In this extreme converg- 
ence I find that lines coincide which make with each other an 
angle of 22 degrees or 11 degrees with the vertical. This 
would seem, therefore, the extreme rotation for my eyes. 1h 
distance of the image in this case is nearly at the root of the 
nose. 
If, however, in extreme convergence, rotation on the optic 
axes takes place to the extent of 11°, this rotation ought to be 
detectable by means of ocular spectra or even by direct obser- 
vation of the eye itself. I determined to try these also. 
method of experimenting with ocular spectra is as follows: 
Standing in a somewhat obscure room, I gaze with the left eye 
(the other being shut) at a vertical crevice in a closed window 
until a distinct spectrum is obtained. Placing myself now 
opposite a vertical line on the wall of the room, with my right 
side toward the wall, I turn my head until my left eye IT (fig. 
9), looking across the root of my nose n, can see the vertical 
ec 
& 
- 
line. I now gaze at a point very near the vertical line, and by 
inclining my head to one side or the other, bring the spectru® 
exactly parallel to the vertical line. In this position, if the 
wall be at some distance from the observer, the axes of the ey® 
may be regarded as nearly parallel as Ife Ib. I now, by® 
voluntary effort, bring the point of sight along the line 1G 
nearer and nearer, until it reaches a near the root of the n0s% 
In doing so the spectrum is always seen to incline to the left 
thus | On relaxing the convergence and looking again at the 
wall, the spectrum retains its inclined position for an apprecia- 
ble time and then gradually recovers its original verticality- 
In similar experiments with the right eye the spectrum ¥ 
always seen to incline to the right thus |. 
I next tried direct observation of the eye itself. As I could 
not find any one with the necessary control over the eyes, } : | 
was compelled to make myself the subject of this observatl0® — | 
While therefore, with the right eye ca I gaze with the left 4 
