14 Transactions oj the Society. 



The plan adopted by the author to obtain these results was to 

 have a rocking stage made in such a way that an ordinary glass slide 

 with its object shall be held securely and focussed ; and as soon as the 

 particular part of the specimen to be photographed is placed exactly 

 in the centre of the field, and the nearest part of the object focussed 

 sharp, or in such a manner as to give the best picture of the object, 

 then the rocking stage is rocked by means of the screws for that 

 purpose till the one side is depressed (say the right side of the slide) 

 to an angle of 7h degrees to the plane of the Microscope stage, and a 

 picture taken. Then, after seeing that the focus is unimpaired by the 

 movement, and that the object has not moved from its central position, 

 the slide is made to rotate about the point of convergence till it is 

 rocked to the extent of 7h degrees inclination to the proper stage of 

 Microscope on the opposite side. Then, on seeing that the focus is 

 correct and the object still in the centre, the picture as seen by the 

 right eye is represented, and a picture is taken. The negatives so 

 obtained are printed, and the prints mounted give the proper stereo- 

 scopic effect. The accompanying mount, which is a photograph of uric 

 acid crystals, shows the result. The results so obtained, when seen 

 by any one, will be admitted to give a better idea of the object than a 

 single picture. 



The rocking slide used by the author consists of a flat stage with 

 a central opening which attaches to the ordinary Microscope stage by 

 springs. From the upper surface of this project two lugs, one in front 

 and one in rear, and from these lugs project inwards towards each 

 other two knife-edges, the edges placed downwards towards the Micro- 

 scope stage ; under these knife-edges, and pressed up against them and 

 rocking on them, is a flat plate of brass cut out flat to receive a glass 

 slide so a3 to allow of the movement of the object, and cut out of such 

 a depth that the surface of the glass and the knife-edges are in the 

 same plane. This plate of brass is extended far enough on either side 

 to be drilled at equal distances from the centre and tapped for a 

 screw ; a thumb-screw is placed in each ; and as one screw is turned in 

 the other is turned out, till the slide is either parallel with the Micro- 

 scope stage proper, or at the required angle to it. 



A little angle of brass being screwed on to the bed-plate of the stage 

 and projecting up in front of one end of the rocking stage, and marked 

 with a zero point at which the rocking stage will be parallel with the 

 bed-plate, and then with 10 degrees marked above and below the zero 

 point, the inclination of the slide in the two positions can be made 

 exact ; and 7£° angle with the stage base is enough to place the slide 

 in the position of a normal to the axis of vision. The author avails 

 himself of this opportunity of recording his thanks to Messrs E. and 

 J. Beck, of Cornhill, London, for the kind attention they gave him. 

 in making the piece of apparatus by which these results have been 

 attained. 



The author gives this account of his success, that others may be 



