A manual of photographic chemistry, theoretical and practical . nting strongly, until the righteye looks at the left wafer, and the left eye at the right wafer, 354 BINOCULAR PHOTOGRAPHY. or else by focusing the eyes for a distance beyond the wafers,which is easily effected by looking at a point midway between,but giving attention to the indistinct wafers on each side, untilthe right eye at length looks at the right, and the left eye atthe left wafer; in both cases the two wafers at first appeardouble, four images being seen, of which two gradually ap-proach until they coalesce, and the result
A manual of photographic chemistry, theoretical and practical . nting strongly, until the righteye looks at the left wafer, and the left eye at the right wafer, 354 BINOCULAR PHOTOGRAPHY. or else by focusing the eyes for a distance beyond the wafers,which is easily effected by looking at a point midway between,but giving attention to the indistinct wafers on each side, untilthe right eye at length looks at the right, and the left eye atthe left wafer; in both cases the two wafers at first appeardouble, four images being seen, of which two gradually ap-proach until they coalesce, and the resulting image appears inthe first case in front, and in the latter case behind thepaper. The mode in which coalescence is effected in bothcases may be thus explained. The perception of a single object, while using two eyes inordinary vision, is due to the eyes being directed to the objectin such a manner that the picture formed in each eye falls onsimilar parts of the retina. If, while viewing an object, oneof the eyes be pressed by the finger, the object becomes. Fig. 49. Fig. 50. R and L represent the two eyes, and A and B the two wafers. double, from the position of the two retinas not correspond-ing. From the same cause, on first trying to fix the two eyeson the two wafers, they appear double until the optic axis ofeach eye (or a line of indefinite length drawn through thecentre of the pupil from the central and most distinctly see-ing part of the retina) is directed fully to each wafer. Whenthis is the case a similar picture falls on similar parts ofeach, and the two objects are perceived by the mind as other less distinct images, one on each side of the prin-cipal one, are due to each eye perceiving its neighborswafer, but on points of the eyes that do not correspond. The cause of the combined image standing out in front orbehind the paper is due. to the mind always referring theplace of an object to the point where the optic axes meet, THE STEKEOSCOPE. 355 and when t
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Keywords: ., bookcentury1800, bookdecade1880, bookidma, booksubjectphotography
