From these various points we thınk we might deduct that convergence of the 
eyes is an inborn property, connected with “viewing” at something or “focusing” 
at something. But it is an error too if one thinks that with binocular vision each 
eye performs the same action as with monocular vision, that is to say, that a direct 
relation exists between the image that our right eye catches and the reflected 
image which our brain makes of it and which appears in our world of observation 
before our right eye. 
The next experiment serves to illustrate this. 
Experiment 3 (fig. II). 
. We take a ruler and put it straight before us against our nose, between both 
eyes. 
We now perceive two rulers in a position dependent on the point we focus. 
Both the rulers *in appearance" are directed towards our point of observation and 
moreover lie approximately in the line of our eye-axes ?). 
But if we blink in turn then the left ruler seems to disappear when closing 
the right eye, and the right ruler when closing the left eye. So it is obvious to 
assume that the right eye projects the ruler mentally near the left eye-axis and 
that the left eye does the same near the right eye-axis. 
The reciprocal relation we know of viewing with one eye appears not to 
exist with binocular vision, that is to say the image which is projected near our 
left eye in our field of observation originates from the right retinal image and 
reversely. 
This experiment itself is extremely important, for it is evident now that we 
see projected nearly on both eye-axes an object which lies in the angle of our 
eye-axes. 
We shall show how this property again solves difficulties with stereoscopic 
vision. 
Perhaps one is inclined to doubt the existence of that relation between 
both eyes and therefore we make the following experiment. 
Experiment 4 (fig. IIT). 
We take a stereoscope either with or without magnifying glasses and put a 
coin under one of the glasses. Soon we shall perceive that only one of the eyes can 
see that coin directly and that only one of the eyes receives a retinal image. 
Another person now can indicate the coin itself as well as the place in which 
the person looking through the stereoscope, sees tie coin, but he can indicate it 
also under the other glass, where there is nothing, and the observer “sees” it 
essentially and completely in the same shape and position as he observed it the 
first time under the other glass. So it is a fact that an action of our brain can 
cause the broadcasting of our mental image originating from the retina of the 
other eye. 
But this experiment teaches us something more, viz. when our right eye is 
better than the left one and we have put the coin under the good right eye, then 
!) We will speak in this article of the “eye-axis”, whereas this is an optical definition. 
In reality the axes mentioned in this article and fig. II originate from points not far from the 
eyes and differ slightly for different persons. 
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