CHAPTER XX 

 CARE OF THE MICROSCOPE 



Care of the Lamp. — The electric lamp lasts longer if it is 

 switched off at pauses between observations. This, if 

 carefully attended to at first, soon becomes a matter of 

 routine, and is then done mechanically as soon as one 

 ceases to look through the microscope. But the 6-volt 

 lamp should not be turned on again until cool, if of about 

 100 watts. These 6-volt bulbs of large size should be 

 locked up when not in their proper socket, because they 

 may be inadvertently screwed into a 110-volt socket, and 

 so destroyed. The lamp may well be fixed at one spot 

 on the table, by screwing down its stand, so that it will 

 not be hable to jar. With care a C-Mazda lamp (110 

 volts) or a 6-volt, 100-watt lamp with coil or ribbon will 

 last for months, with several hours of daily use. 



Care of the Ground Glass Disc. — This should be as 

 thin as practicable, and finely ground on both sides. 

 The surfaces may be made fine by grinding two discs 

 together with carborundum flour and water. If wiped 

 dry, not washed, a fine deposit is left in the scratches, 

 which perceptibly improves the light. The disc of ground 

 glass may be warmed and rubbed on one or both sides with 

 tissue or lens paper moistened with a nearly saturated 

 solution of magnesium sulphate. This should be polished 

 off dry, so as to leave an almost invisible residue, sufficient 

 to exclude direct light. After a damp day, it may crys- 

 tallize, and require replacing. 



Care of the Light Filters. — The plane surfaces of these 

 should be carefully cleaned and kept free from finger 

 prints. If made of gelatin mounted in balsam, they must 

 not be heated by being too close to the lamp, or by having 

 the free circulation of air around them shut off. Also in 



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