100 PHOTOMICROGRAPHY 



towards the microscope critical illumination is easily 

 obtained. The light is improved by dissolving a little 

 camphor in the paraffin, and if the wick is properly 

 trimmed, and the condenser correctly adjusted, it is 

 quite brilliant enough for high -power work. A good 

 form is shown at Fig. 30. 



Lamp Stands. Whatever radiant is made use of, 

 the lamp must be adjustable in height and from side 

 to side, so that the light can be accurately centred to 

 the microscope, and when an optical bench is employed 

 the lamp should be adapte4 to it in some suitable way. 

 It is very convenient to attach the collecting lens 

 and also the light filters to the lamp, as in Fig. 30, 

 but they can be carried on independent stands if pre- 

 ferred. 



It is also very desirable to enclose the radiant in a box 

 or lantern to screen off extraneous light, and a specially 

 made one is often supplied with large cameras (Fig. 3). 

 An ordinary projection-lantern with lens and condenser 

 removed answers the purpose very well (Fig. 2), or a 

 metal chimney or shade can be made to surround the 

 light (Fig. 29). A large dark-room lamp may even be 

 adapted, the red glass being replaced by a sheet of metal 

 pierced with a suitable aperture, and carrying an iris 

 diaphragm if possible. 



Selection of an Illuminant. The advantages and draw- 

 backs attending the use of the majority of illuminants 

 have now been mentioned, but it may be convenient to 

 summarise the points on which the selection of one or 

 another mainly depend. Sunlight may be left out of 

 consideration, and the choice made from the artificial 

 illuminants. The decision usually turns on the avail- 

 ability of electricity or gas, and the question of expense. 

 Electric light is no doubt the most convenient, and 

 should be chosen whenever possible. 



When direct current is available the selection should 





