SIMPLE MICROSCOPE. 5 



fore finger is placed at the top of the tube to close it; 

 the tube is then put into the water until the lower 

 end is close to the object, when, on suddenly re- 

 moving the fore finger, the water will rise in the 

 tube, carrying the object with it. The fore finger is 

 then again applied to the tube, and, as thus held, the 

 water will not run out. The tube is then held over a 

 watch-glass, or a slide, upon which the water and 

 object will fall on removing the fore finger. 



A small glass spirit-lamp will be found very useful. 

 The spirit for burning should be methylated alcohol, 

 or wood-naphtha. As these spirits are inflammable, 

 great care should be taken to keep the stock-bottle 

 away from a candle or other flame, when filling the 

 lamp. 



Achromatic condenser. A very important piece of 

 apparatus, when high powers are used, is the achro- 

 matic condenser ; it is not, however, usually supplied 

 with the cheaper microscopes. It consists of a brass 

 fitting, placed beneath the stage, into which an ob- 

 ject-glass is screwed, in an inverted position, i. e. the 

 small end of the object-glass being placed uppermost. 

 It serves to condense the light to a focus upon the 

 object, so as to illuminate it more brightly ; and as it 

 can be elevated or depressed by a milled head and 

 rack-work, the object can be viewed by either con- 

 verging or diverging rays. 



Simple microscope. For examining the larger 

 kinds of objects, and for dissection, a simple micro- 

 scope is very useful. This consists of a stand, a 

 stage, and an arm supporting a simple lens or com- 

 bination of lenses, but without the body of the com- 

 pound microscope (as the ordinary microscope is 

 distinctively called). For most purposes, common 

 plano-convex or doubly convex lenses are sufficient 

 to form the object-glasses of a simple microscope. 

 With the best microscopes, an " erector," or tube 



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