MICROSCOPES. 237 



pillar. It is more difficult to get the reflected light with the 

 candle than by day light, but many of the objects appear 

 to much greater advantage ; the candle should be placed at 

 the distance of about twelve inches, not too high, and in a 

 straight line with the mirror. 



Description and Application of the Different Powers. 

 This microscope has five different powers, so arranged that 

 objects may be viewed from the size of a large beetle or 

 moth to the most minute animalculee. These powers are 

 marked Nos. 1, 2, 3 ; No. 1 is the lowest power, and is cal- 

 culated for viewing opaque and large objects, and should be 

 used without the body. No. 2 is the next power, and is 

 calculated for viewing all the objects of the size of those in 

 the slides ; the next power is produced by combining the 

 Nos. 1 and 2 together, which may be called the third 

 power; it magnifies 2,500 times, and is adapted for viewing 

 the animalculee, &c. The fourth power is in a conical cell, 

 marked No. 3 ; with this power an object is magnified 

 26,000 times with the body ; the fifth or greatest power is 

 in a flat cell, and magnifies an object 62,500 times with the 

 body, which is equal to the largest compound microscopes ; 

 it should only be used for extreme minute objects, and 

 without either of the other powers ; as the object and the 

 lens come extremely near when it is used, care must be 

 taken, by a very delicate movement of the stage, that they 

 do not come in contact with each other in getting the pro- 

 per focus. To prevent this, if a drop of water is to be ex- 

 amined, place it between the slips of glass, and if these will 

 not permit the lens to come near enough, place a piece of 

 thin talc upon a piece of glass. Objects should first be 

 viewed with the low powers, that the whole of them may be 

 seen, and the higher ones can then be used in gradation. 



Achromatic Microscope. One of the most valuable con- 

 tributions to the science of the microscope is that of the 

 introduction of achromatic object-glasses to these instru- 

 ments. These lenses represent the object better defined, 

 and clearer, and also free from the tints and coloring, usually 

 found in other instruments ; and although they have but re- 

 cently come into use, their great superiority is unquestioned, 

 the only bar to their more general use being the great ad- 

 dition in cost. Fig. 755, next page, represents a ^ modern 



