178 The Microscope. 



the receptacle prepared for it ; the body is racked down, and placed 

 in a vertical position, and the stand is lifted into the case, where it 

 remains with its front looking at the back wall of the box. The 

 door is then closed and locked. If there are children around 

 that cannot be controlled, the key would better be carried in the 

 owner's pocket. Two minutes' brutal usage will do more injury 

 to a good stand than months of proper treatment. No one but 

 the microscopist should ever touch the objectives, and he should 

 carefully avoid the contact of his fingers with the lens. Optical 

 glass is soft and easily injured. The owner would do well to act 

 accordingly, for a scratched or broken objective is a ruined one. 



Dust is an insidious and a dangerous enemy to the microscope. 

 It gets into the bearings and the movable parts, and harms them. 

 The microscopist should therefore often wipe the stand with a 

 soft old handkerchief or a fine chamois skin. The latter is the 

 better since the fibres. from the handkerchief often become a 

 source of trouble. No liquid should be used ; alcohol should 

 especially be avoided as it will remove the lacquer. The rack 

 and pinion bearings may be occasionally and sparingly touched 

 with the porpoise oil used by the jewellers, or with very superior 

 sewing-machine oil. Exceeding small quantities must be used, 

 and the parts at once wiped almost dry, otherwise the oily sur- 

 faces will collect the dust, and the last state of that microscope 

 will be worse than the first. The dealers use soft and thick 

 grease for lubricating purposes, or a refined tallow. The parts 

 of a well made stand need lubricating only at very long intervals. 

 They will work well if kept perfectly clean and free from dust. 



The microscopist will sometimes be annoyed by one or more 

 indefinite specks or spots apparently in the field, but whether- 

 on the eye-piece or on the objective he cannot decide. That they 

 are not on the object or the cover glass is deterniined by moving 

 the slide, and if the specks remain stationary they are either on 

 the ocular or on the objective. To discriminate between these, 

 rotate the ocular; if the offending particles move they are on it; 

 if not, they are on the objective. If on the former, the two lenses 

 may be unscrewed and carefully wiped by the Japanese filter 

 paper ; if upon the objective the front lens may be guardedly 

 touched with the Japanese paper, or the back combination very 

 cautiouly swept with a soft camel's hair brush. This must be 

 carefully done, and the brush must be scrupulously clean, other- 



