1 6 THE MICROSCOPE. 



object. I should recommend you to practise yourself 

 with the examination of objects that require low 

 powers for some time before you try your hand on 

 such as require high powers and very accurate and 

 fine focussing. You will at first mistake small particles 

 of dust, perhaps, for something connected with the 

 object you are examining. In the examination of 

 drops of water, numerous bubbles of air will present 

 themselves in questionable shapes, and you will won- 

 der what they are. In placing the thin glass over the 

 drop of water, be careful to let its edge first touch the 

 water, and then let it slowly fall on it. The surplus 

 water should be wiped off, and care must be taken 

 that the upper surface of the cover does not get wet, 

 otherwise, if you are using a high power, you will get 

 a misty view. Carelessly dropping or flopping the 

 cover upon the drop of water is sure to produce air- 

 bubbles, which may sometimes interfere most inop- 

 portunely and inconveniently with your getting a good 

 view of the organ of some restless little animalcule. 

 Never interfere with the lenses of the object-glasses; 

 all that is necessary is to wipe the lower surface with 

 a clean bit of wash-leather. Never leave the object- 

 glasses uncovered when not in use, and never examine 

 a drop of water without a thin glass cover over it. 

 Do not touch the lenses of the object-glasses, or you 

 will make them dim and misty. Attention to these 

 instructions will repay you for your trouble, and save 

 disappointment and probably expense. 



