SPECIAL APPARATUS 27 



an angle, because this is most convenient for comfortable 

 use. This last point is most important, for one may 

 have to spend hours searching through films with this 

 method, and it is most wearying to have to work in an 

 uncomfortable position. 



Behind the mirror, and standing a little way back 

 from it, there is a Nelson's aplanatic condenser (Wat- 

 son) with iris diaphragm, and immediately behind 

 this again is fixed a rectangular all-glass water-tank. 

 This small tank has an outlet pipe above, and an inlet 

 pipe below, connected by means of rubber tubes with 

 a sink and a cold-water supply respectively. The water 

 is kept circulating through this tank when the apparatus 

 is in use. Lastly, behind the tank is the burner of 

 a 1-ampere Nernst lamp. 



Above the microscope and set at an angle corre- 

 sponding to its tilt a rigid wooden board is arranged, 

 being fixed to the ceiling above and, by means of a pair 

 of legs on either side of the microscope to the bench 

 below. The board, which is about ten inches in width, 

 by seven-eighths of an inch thick, has a slot cut into it 

 in which a box camera can easily slide up and down and 

 be capable of being fixed at any point by means of a 

 screw clamp. The camera is fitted with a shutter 

 (instantaneous and time exposures) the aperture of 

 which is connected with a "high-power projection eye- 

 piece" (Watson) by means of a flexible velvet collar. 



The Nernst burner, the cooling tank, the two 

 condensers, and lastly the camera must all be very 

 carefully centred to the microscope, and immovably 

 fixed so that the whole apparatus may always be ready 



