Abstract
The cell-layers of retina of human eye consists of two kinds of cells. The one called“Zapfen” hasa strong visual power and functions in daylight and the other called “Stiibchen” functions in dark andhas about one-fifteenth visual power of the former, Moreover, the former has color sensation butthe latter has not. Man of normal vision in daylight, but of weak visual power in dark has injured“Stiibchen” and is called night-blinder. So, the illuminating engineers must have not only thegood visual power but also good sensation of light.
The sense of deepness (“Tiefenwahrnehmung”) is occured by the single sight of two eyes, the so called“functions of binocular sight.” This function causes a man of latent strabismus the fatigue of eyes (“Latentes Schielen Heterophorie”), but the man of single eye does not feels this fatigue.
The advantages of having two eyes are (1) sharp sense of deepness, (2) wide field of vision and (3) not becoming blindness when injured one eye.
When one eye is good but another is injured, one uses the better one only and his visual poweris never equal to the averaged power of two eyes.
