ABSTRACT
There are few subjects which have elicited more attention from philosophers than the phenomena of vision, and several theories have been promulgated which attempt to explain the very remarkable condition of single vision with a pair of eyes. The eye is a singularly beautiful piece of mechanism, most perfectly adapted for enabling people to acquire correct knowledge of the creations by which they are surrounded. The eyeball consists of four membranous coats, namely sclerotic coat, choroid coat, cornea, and retina. Looking through the cornea from without, people perceive the pupil of the eye, an opening formed in the coloured membrane within, and nearly in the centre of the cornea. The coats of the eye enclose the aqueous humour, the vitreous humour, and the crystalline humour, the last having the form of and acting as a lens. The means of adjusting the lenses as to magnifying power will readily suggest themselves to any one constructing either the binocular camera or stereoscope.
