HORIZONTAL CAMERAS 9 



phragms are carried in a recess on the other side of the 

 holder, which is fitted with a dovetail slide for transverse 

 motion on a cross-piece of wood carried on a vertically 

 extensible brass tube an ordinary telescopic bull's-eye 

 carrier. These two motions provide a rough means for 

 centring the condenser. 



An important point in both these arrangements is the 

 means adopted for removing the camera when it is 

 desired to examine the object directly through the 

 microscope. In the first, its carrier slides off the base- 

 board ; in the second, the camera can be lifted off bodily, 

 but in either case it can be replaced without any dis- 

 turbance to other parts of the apparatus. In other 

 cameras the microscope and illuminant are carried on a 

 turn-table which can be readily swung in or out of the 

 optical axis ; but this plan is rather difficult for an 

 amateur to carry out satisfactorily unless well provided 

 with tools. In professionally made outfits such as that 

 of Mr. Barnard (Fig. 8), the turn-table works excel- 

 lently. 



Focussing Arrangements. A long extension is of great 

 advantage, in that it permits of a wider range of magnifi- 

 cation from one combination of objective and eyepiece, 

 and when a short camera has to be utilised it may even 

 be advisable to add an extra bellows extension, such as is 

 made by Messrs. Lancaster and other firms, to the back, 

 or a conical tube blackened inside, to the front. A long 

 bellows necessitates the use of a mechanical focussing 

 gear to reach the fine adjustment of the microscope 

 while examining the image on the ground glass. In the 

 camera above described it consists of a brass rod 

 carried on two bearings screwed to the baseboard ; a 

 milled head is soldered on one end and a pulley on. the 

 other. A piece of thread is used to form a band round 

 the pulley and fine adjustment head, and motion is 

 thereby conveyed with very fair delicacy to the fine 



