PAK? -£ 
THE MICROSCOPE, 
A compound microscope consists of four parts. 
1, The body, which contains the magnifying apparatus. 
2. The stage, which supports the object that is to be 
examined. 
3. The mirror, which illuminates the object. 
4, The stand, which connects the whole together. 
The Bopy consists of a tube, one end of which carries 
the objective, the other the eye-piece. The objective is placed 
at that end next the object to be examined. It consists of 
an achromatic combination of lenses, and may be either a 
high or a low power. The higher the power, the more the 
objective magnifies, the smaller are the lenses, and the 
shorter is the focus. So that the higher the power the 
nearer has the objective to be brought to the object in order 
to see it. The European opticians give their objectives 
numbers—the higher the number the higher the power; 
but the numbers of the different makers do not correspond. 
Thus a No. 7 of Siebert equals a No. 9 of Hartnack. The 
English and American opticians call their objectives by the 
supposed focal length of a single lens that would magnify the 
same. Thus, a glass that will magnify about 50 diameters 
with a body 10 inches long, is called a “ one-inch,” and one 
that magnifies about 200 diameters is called a “ quarter- 
inch.” Hartnack’s No. 4 is about equal to an “inch;” his 
No. 7 toa “ 3th;’ and his No. 9 toa “th.” 
