Note c — BOOK IV.

Suppose the Eye had the Retina, or back part flat for the Reception of the Images, as in Fig. 1. ABA: it is manifest, that if the Extremes of the Image AA were at a due focal distance, the middle B would be too nigh the Crystalline, and consequently appear confused and dim; but all Parts of the Retina lying at a due focal distance from the Crystalline, as at ACA, therefore the Image painted thereon is seen distinct and clear. Thus in a dark Room, with a Lens at a Hole in the Window, (which Sturmius calls his Artificial Eye, in his Exercit. Acad. one of which he had made for his Pupils, to run any where on Wheels). In this Room, I say, if the Paper that receives the Images be too nigh, or too far off the Lens, the Image will be confused and dim; but in the Focus of the Glass, distinct, clear, and a pleasant Sight.