296 APPENDIX. 



tube, to which it is clamped by the screw d. Just above 

 the tube is placed the "stop" for shutting the light off' at 

 any moment from the camera plate; it consists of a light 

 hinged flap, which, by turning a small handle (not shown 

 in the figure), may be made to fall over the aperture. 



The microscope is put in the centre of the stand, being 

 held firmly in place by three projecting blocks provided 

 with strong wooden buttons for clamping the foot, and 

 there is a round hole in the centre of the stand st, so that 

 the apparatus can, if desired, be used in the horizontal 

 position, the light being sent directly through the hole. 

 It is well to unscrew and remove the whole of the upper 

 part of the microscope tube (Fig. 1, '), the cloth-lined 

 tube at the lower end of the camera being made to fit 

 over the lower and larger part (t). 



When the apparatus is in the position shown in the 

 figure, the ground-glass camera plate is horizontal, and it 

 would be extremely awkward to lean over and observe 

 the image upon the plate and at the same time adjust the 

 focus. To obviate this difficulty the plane mirror m is 

 provided; it is inclined at a convenient angle, so that the 

 image on the plate is reflected towards the observer stand- 

 ing behind the microscope. When focussing, the upper 

 part of the apparatus as well as the head of the observer 

 may be enveloped in a loose black cloth. 



It is necessary to employ bright sunlight (or some other 

 intense and actinic source of light), which should be 

 allowed to pass through a glass vessel containing a solu- 

 tion of amrnonio-sulphate of copper, so as to render the 

 light mono-chromatic. It is then received on the mirror 

 of the microscope (supposing the apparatus to be vertical) 

 either directly or after traversing a condensing lens, and 

 is reflected by the mirror up through the object and the 

 tube of the microscope in the ordinary way. An objective 

 of any magnifying power, even an immersion may be em- 

 ployed, provided there be light enough'. With the same 

 objective greater or less magnification is obtained accord- 

 ing as the camera is raised or lowered. 



The object is focussed upon the ground-glass with the 

 utmost exactitude. The light is then cut off, the mirror, 

 w, removed, and the sensitized plate substituted for the 

 ground-glass plate as in the ordinary process. 



Mr. G. Giles has devised a simple mode of adapting 



