202 Mr. S. Rowley on a New Theory of Vision. 



At B, fig. 3 (the board duly widened), at a point 4^ inches 

 to the right of B, and a point of 4-^j- inches to the left, station 

 these pins, so that the rings shall be parallel to the eyes of the 

 observer. At the points A, T, V, set simple pins. Now on 

 converging the axes toward A, till the right eye's image of the 

 pin at T and the left eye's of the pin at V are hidden in the 

 combined images of the pin at A, the images of the rings will be 

 apprehended in their true visible places. 



To make another experiment of the kind to which the last be- 

 longs, on a glass of a window situated at a convenient height 

 stick a number of wafers, placing their centres in a horizontal 

 line and separating the adjacent centres by a distance less than 

 that between the centres of the eyes, but being extremely careful 

 to make all these distances exactly equal. Direct the axes 

 through the centres of two adjoining wafers, each axis through 

 that centre lying on its own side, and presently all the visible 

 images (except usually the left terminal image of the right eye's 

 series and the right terminal one of the left eye's) will be recog- 

 nized by consciousness in their true visible positions. 



If the adjoining centres of the wafers are very close to each 

 other (as a little over ^ inch, supposing the wafers to be 4 inch 

 in diameter) and the eyes at a short distance, say, 4 inches, the 

 curvature of tl*e surface of vision will be plainly appreciated, and 

 if the plane of the axes be turned on the line joining the inter- 

 section of the axes to the centre of the interval between the eyes 

 from a coincidence to an angle with the horizontal plane passing 

 through the centres of the wafers, the curvature of each eye's series 

 will be separately appreciated. 



An experiment of the same kind may also be made by means 

 of the similar figures lying at equal distances in the surface of a 

 papered wall. 



If the experimenter will station himself facing such a wall 

 and converge his optic axes so that the axis of his left eye shall 

 pierce the centre of some figure in front of him, and that of his 

 right eye the centre of the next one to the left of the other, 

 then shortly each eye's image of the papered wall will, to his 

 consciousness, take its true visible position at the distance of the 

 convergence of the axes — the images of the figures appearing 

 smaller or larger, according as the distance of the point of con- 

 vergence is less or greater. A variation (from the standard) of 

 the distance between the centres of the figures of the wall will 

 produce a seeming elevation or depression of the visible images. 

 The cause of this last, as well as that of the principal phenome- 

 non, will be explained when it shall have been explained why the 

 lateral images of an object which is at a greater or leas distance 



