THE MICROSCOPE. 11 



ment is applied to the tube of the Microscope when 

 placed at right angles with the stem, in such a way 

 that a person looking into it sees the object directly 

 under his eye, so that he may easily draw its form 

 on a piece of paper placed underneath. 



Amongst the accessory apparatus, are various 

 arrangements for concentrating the light on the 

 objects which are placed for examination under 

 the Microscope. Amongst these combinations, is 

 one called the achromatic condenser. This consists 

 of a series of lenses, which are placed between the 

 mirror and the stage, and which may consist of 

 an ordinary object-glass. The stages of the larger 

 kinds of Microscopes are fitted up with a screw 

 or slide, by which the condenser can be fastened 

 beneath and adjusted to the proper focus for 

 throwing light on the object examined. Instru- 

 ments have also been invented, called illuminators, 

 which are intended to supplement or assist the 

 mirror in throwing light on the object. These are 

 things, however, about which the beginner need not 

 trouble himself. They are amongst the apparatus 

 which contribute to the perfection of the Micro- 

 scope, but are not amongst its necessary accom- 

 paniments. 



The same may be said of the polarizing ap- 

 paratus. The use of polarized light adds greatly 

 to the beautiful appearance of many objects under 

 the Microscope, but it is only in a very few 

 instances in which it can be said to furnish a 

 means of distinguishing one object from the other. 

 It may, therefore, be left to the time when the 

 observer has gone through some little practice 

 with his instrument, or has saved enough money 

 to buy the necessary apparatus. 



Having said thus much with regard to ap- 

 paratus, we will now give some directions for the 



