258 now TO wo UK 



He also suggests that in objects of thickness the near surface should 

 be focussed for the one and the more distant for the other picture. 



Dr. Maddox produced stereoscopic pictures on one of the plans 

 proposed by Prof. \Yheatstone, and for this purpose he made a small 

 $1 x if inch slide-holder of brass plate having a central aperture 

 and a ledge at the top and bottom, in the direction of the length, 

 turned up square at right angles. Opposite the centre, the ledges 

 were pierced by a small hole about 1 of an inch from the angle of 

 junction ; two thin strips of spring brass being cut to the width of 

 the ledges, about i^ inches long and slightly curved, had each a small 

 hole drilled in the centre. Two pieces of hard wood were cut into 

 equal triangles, which were each fixed on a brass pin in such a 

 position, that when the little triangular blocks were resting with their 

 obtuse angles on the upper surface of the brass slide, the other end 

 of the pins passed through the hole in the small strips of spring 

 brass, then through the holes in the ledges, the pins being now turned 

 up at right angles to prevent them from being carried out of the holes 

 by their springs. An ordinary glass slide with the object set up 

 was placed between the springs (and rested by its under surface 

 near the edges on the upper or horizontal surfaces of the two 

 small blocks), being clipped by them sufficiently tight to prevent 

 falling out, when the slide was placed vertically on edge. On 

 depressing either end of the slide, the object could be made to 

 assume an obliquity to the objective, equivalent to the angle found 

 between the surface of the little triangular blocks and the edge 

 of the depressed slide when resting on the plane of the brass 

 holder. This method answered very well for opaque objects illumi- 

 nated by the Lieberkiihn. The slide holding the object being first 

 centered and focussed from the point where the least displacement 

 of the focus appears on depressing each side equally and alternately, 

 now depressed and re-focussed if necessary, to furnish the first 

 picture, then similarly treated on the opposite side of the centre 

 to furnish the second. The resultant images giving a stereo-picture ; 

 when the left depressed view is taken on the right-hand side of 

 the plate, and rice versa, the images need not be reversed after 

 printing. He also used for transparent objects Mr. Wenham's and 

 Mr. Smith's plan for stopping off alternately in front the right and 

 left halves of the objective by a small cap with a semicircular 

 aperture, equal generally to half the area of the front lens, while 

 with the highest powers, he only makes a slight alteration in the 

 position of the object and incident light for the second picture. 

 With the parabolic illuminator he did not succeed equally well. 

 M. Nachet, jun., used his polished cone of glass with a central 



