184 THE USE OF THE MICROSCOPE 



prisms are best cleaned by the maker, unless the micro- 

 scopist is expert in this operation. However, the objectives 

 (or their exposed surfaces) and the eyepieces can be kept 

 optically clean. The magnifier may be kept under a bell 

 jar when not in use; and an included vessel of fused calcium 

 chloride will keep lenses and prisms dry, and free from 

 film. This is especially needed in a laboratory where 

 autoclaves are steaming. 



Care of the Greenough. — The prisms are cemented 

 in one block (No. 2 Porro prisms of Czapski-Eppenstein, 

 57), and can in some makes be taken out and cleaned 

 without much trouble. In putting them back, an object 

 must be observed to see if both images exactly coincide. 

 If not, the prisms must be shifted till they do. The 

 objectives are often hard to clean on the back, but a roll 

 of filter paper with lens paper round one end, or a long roll 

 of lens paper, can be used when the ends of the objectives 

 do not unscrew. The adjusting screws of these objectives 

 should only be altered by the makers. The Greenough 

 should be covered when not in use. 



Care of the Hand Lens. — If this is a cemented doublet 

 or triplet, it should not be dropped. If the cement gets 

 sprung, however, the lens can usually be mended by 

 removing it from the metal socket, cleaning, and recement- 

 ing. If it is held in by turned metal flanges, it should 

 be carefully cleaned with xylol, and have either one side 

 covered with balsam, or be altogether immersed in balsam 

 in a vessel, and put in a warm oven, at about 100° C, 

 or more, for some hours or days, until the balsam has 

 returned between the lenses. 



Practical Points 



1. Switch off the lamp when not looking through the 

 microscope. 



2. Treat the ground glass at regular intervals with magne- 

 sium sulphate (or use freshly ground glass, wiped dry from grind- 

 ing, not washed). 



3. Do not expose the gelatin light filters to unnecessary light 

 or to direct sunlight. 



