28 Avoiding the Use of the 



fits the condenser, the centre of ^Yhich is elevated to such a height 

 as to be opposite the tube of the microscope. Behind this lens the 

 alum cell fits into a slit made to receive it in the upright pieces. 

 Behind the condenser is a firmly sliding piece of wood, in which 

 holes are cut to receive tightly the feet of the microscope. 



The camera is. connected with the microscope as follows. To 

 the front of the camera is fixed a wide metal tube, which is con- 

 nected to a somewhat smaller one by a joint of cloth. 



This smaller tube ends in one which loosely fits the tube of the 

 microscope, and which is lined with thick wash-leather in order to 

 exclude all light. 



Supposing then that one wishes to photograph any part of an 

 object. The slide is fixed in position by means of the springs 

 usually attached to the stage of the microscope, and its draw-tube 

 pulled out. It is then inclined to a horizontal position, the mirror 

 turned aside, and its feet fixed iti the holes cut for their reception in 

 the sliding piece which is then pushed back, so tbat the tube slips into 

 the collar of the camera. The draw-tube is then replaced from the 

 inside of the camera, the flange, with which it is generally provided, 

 tbus effectually shutting out any light that might otherwise enter. 

 The alum cell which should contain a thickness of about half an 

 inch should next be placed in the slit and filled with a concentrated 

 solution of alum. The apparatus should then be placed across a 

 table in front of an open window, out of which the mirror should 

 be made to project so as to be out of shadows cast by the eaves, the 

 base-board being so placed that the reflexion may take place at as 

 acute an angle as possible. The -window-blind should then be let 

 down so that it hangs just above the condenser and turned as 

 dark as possible, by which means the nuisance of a focussing cloth 

 is avoided. Then seating oneself so as to be able to watch the 

 focussing screen, the light is thrown on to the object, and the con- 

 denser focussed so as to throw a distinct image of the sun on the 

 slide. After which the light is cut oS' by turning round the wheel 

 of diaphragms preparatory to inserting the sensitized plate. 



Here I would remark that it is a good plan to close all the holes 

 in the diaphragm with pieces of nonactinic paper with the excep- 

 tion of one of moderate size, and to loosen the screw on which it 

 pivots in order that it may turn as easily as possible. 



Then having replaced the focussing screen by the dark slide 

 and raised the shutter, the exposure is made by turning round the 

 diaphragm wheel so that the opening in it may pass swiftly across 

 the aperture in the stage ; the shutter is then closed and the plate 

 taken to the operating room for development. 



Ground glass is rather too coarse a material for the focussing 

 screen in micro-photography ; for this purpose a piece of patent plate 

 over which has been poured a film of mucilage of starch, or some 



