4 Transactions of the Society. 



that the utmost stiffness is obtaiued. The two castings carrying 

 the camera portion are braced togetlier at each end, and at their 

 middle, by small cast cross-bracing pieces. In each case the cast- 

 ings are fastened together by means of screws and bolts, holes 

 being left in the castings to allow these to pass through. There 

 is, therefore, no fitting or drilling of any sort required in putting 

 these together. 



The ]iortion of the apparatus to carry the Microscope and 

 illuminating apparatus is also on a pair of castings, these being 

 triangular in shape, and again braced together in the same manner 

 as are the main castings. The latter pair of castings are supported 

 at the end away from the camera on a metal cone, which allows 

 them to be swung out of alignment with the rest of the apparatus 

 in the manner already well known in many designs of photo- 

 micrographic apparatus. The female part of the cone is on the 

 swinging tail-piece, whereas the male portion is carried at the 

 end of the main castings. The other end of the swimjin" tail- 

 piece IS supported on a segmental arm, and is resting on two 

 points. It therefore satisfies the requirements of the geometric 

 clamp in so far as it requires to have one degree of freedom, 

 allowing it to rotate on a vertical axis. It is supported at its 

 centre on the cone, and its two other points of support are quite 

 free. No shifting of tlie part other than in the direction re- 

 quired is possible, and it differs essentially in that respect from 

 other arrangements generally used, where a bolt or metal pin is 

 used as a centre of rotation. 



On the top of the main castings, supporting the whole appa- 

 ratus, two stiff metal rods are placed. In this case they are iron 

 brass-cased, thus ensuring rather greater stiffness than can be 

 obtained with brass rod alone. These rods are fastened down 

 firmly to the castings, and the camera slides to and fro on two 

 V grooves on one side and on a plane surface on the other in the 

 manner already described, both the front and back of the camera 

 being so supported. On the portion of the apparatus carrying the 

 illuminating arrangement and the Microscope, tJie same method is 

 adopted ; the Microscope is carried on a cast-iron baseplate, the 

 necessary V grooves and plane surface being all in one casting 

 from one original patteriL ISTo more work is done to this part 

 than to file off the roughness of the casting from the inside surface 

 of the V grooves, and from the plane surface on the opposite side. 

 The plates carrying the illuminant, any subsidiary condensing 

 lenses, water trough, colour screens, or cells, are all supported in 

 the same manner, and each one has a quick-acting clamp rigidly 

 fastening it down in any required position. 



In all cases the clamp is of a simple character, and consists of 

 a metal bar, which engages on each side of the casting on which it 

 rests, a quick-acting screw passing through it and the base-plate ; 



