A Geometric Slide Fhotomicrographic Apparatus. 5 



the bar therefore, on manipulating the screw, is drawn by it against 

 the inner edge of the casting, and the sliding portion is drawn down 

 on to its supporting rods. Such a method of clamping is obviously 

 superior to even that in which subsidiary appliances are carried on 

 a triangular metal bar, as in tlie latter case the clamp is at the side ; 

 and those who have worked with such an arrangement realize that 

 some displacement, however small, is unavoidable if the clamping 

 screw has any slight undue strain put on it. 



The camera itself is supported on vertical rods, which are firmly 

 fixed to the geometric slides already described. This allows of the 

 camera being moved in a vertical direction to any required position, 

 so that where Microscopes of different sizes have to be used, or 

 where it is not possible to specially fit the apparatus to a Micro- 

 scope of a particular height, the camera can be raised to suit the 

 required conditions. There is nothing special about the camera 

 portion as such, except that on one side a small white screen is 

 supported, so that when the Microscope is thrown out of alignment 

 on its swinging tail-piece, an image may be projected on the small 

 subsidiary screen. The preliminary adjustment of the instrument, 

 either in the way of centring the substage condenser, the illu- 

 minant, or any subsidiary condensing systems, as well as altering 

 the position of the object itself, may be effected by directly observ- 

 ing the projected image : final focusing must, of course, be done on 

 the ground or clear-glass screen in the usual manner, but the 

 advantage of this additional reflecting screen is considerable. 



The apparatus here shown is designed to be as far as possible 

 universal in its applications. It may be used as a horizontal or as 

 a vertical camera ; it may be inclined at an angle of 45^, should 

 such for any reason be required ; it may be used in a manner that 

 I shall indicate, for metallography, in which the source of light is 

 usually placed at right angles to the direccion of the optic axis of 

 the Microscope ; or it may very conveniently be used for photo- 

 grapliing large specimens which require to be in a horizontal 

 position, or in photographing other objects which are conveniently 

 supported in a vertical position. 



If required for use as a vertical as well as a horizontal camera, 

 the camera portion is carried on a subsidiary iron frame, wliicli rests 

 inside the main supporting castings. This frame is fastened at the 

 end near the Microscope in such a way that it can be swung and 

 supported vertically (fig. 3). To ensure rigidity while in thi& 

 position, an additional strut is provided, which clamps on the side 

 of the apparatus, s© that the camera itself is supported on the 

 vertical iron frame, which is again braced to the main castings. In 

 this case it is obvious that the position of the camera in relation to 

 the Microscope would require some alteration, and the manner in 

 which the camera slides up and down on its metal rod supports 

 provides for this. The illuminating appliances remain in the same 



