of Edinbitrgh, Session 1883-84. 
433 
Monday, 21st January 1884. 
EOBEKT GEAY, Esq., Vice-President, in the Chair. 
The following Communications were read : — 
1. On Distant Vision. By E. E. Maddox, M.B., C.M. 
Communicated by Prof. Crum Brown. 
I believe it is universally assumed by English physiologists that 
the zero of accommodation is naturally associated with parallel visual 
axes as in the “ Primary Position ” of Helmholtz, Listing, &c.* 
It is self-evident that when even in actual life a body is viewed 
at infinite distance the visual axes must be parallel. It is also 
well known that the nervous connection between convergence and 
accommodation is a most delicate and susceptible one, and is none 
the less so naturally because it is capable of being overcome for a 
time by various conditions. It is therefore quite reasonable to 
suppose that when the ciliary muscle is at rest the converging 
mechanism should be so likewise ; and to expect that the invariable 
association of the visual actions of a life-time should be impressed, 
if not at birth, as Porterfield suggested, “ by an original, connate, 
and immutable law,” at least by “ dint of habit,” upon the very 
constitution of the governing ganglia. 
That this is not the case will be evident from the following 
experiment : — Let two small round holes be made through a piece 
of paper, nearly two and a half inches apart. Hold them hori- 
zontally about six inches before the face, and look through the left 
hole with the left eye at some very distant object. Four images 
now, of course, appear as shown in fig. 1. Each hole throws a direct 
image nearly upon the macula of its corresponding eye, and another 
image obliquely upon the outer part of the retina of the opposite 
eye. The appearance which results is represented in fig. 2. The two 
* “In investigating the movements of the eyes, we take as a normal point 
of departure a position of the eyes which corresponds to a minimum of inner- 
vation of their muscles. In this position, which is called the 'primary position, i 
the visual lines are directed straight in front, parallel to each other, and in ' 
the same horizontal plane.” — Landolt. 
