l6 AQUATIC MICROSCOPY FOR BEGINNERS. 



need not be expensive, but it should be a good and 

 satisfactory glass, not only at the outset, but when the 

 student becomes an expert microscopist; it will thenal- 

 ways be useful. Such objectives are made by several 

 American opticians, and included in what they call 

 their "Students' Series." When in focus, the distance 

 between the front lens and the surface of the object — 

 the "working-distance" — is large, and there will 

 therefore be no trouble in using it; and with the two- 

 inch, or the "A," eye-piece, the magnifying power 

 will be about forty-five diameters, or a little more than 

 two thousand times. 



After the student has been using the one-inch ob- 

 jective for some time, and his eye has become edu- 

 cated, he will begin to catch glimpses of minute ob- 

 jects beyond the ability of the low-power glass to ex- 

 hibit properly. Then he will wish for soniething 

 more, so that he can look deeper into the little things 

 of Nature. What shall it be ? 



The opticians make ^, ■^^, and even -^-inch objec- 

 tives, which magnify enormously, cost frightfully, and 

 can be successfully used only by accomplished micros- 

 copists on large and first-class stands. To the be- 

 ginner, even after considerable experience with the 

 low-power lens, any objective higher than the ;^ of ^ 

 will be useless. With either of these glasses he will 

 be well equipped for quite extensive microscopical 

 study, until he is ready to undertake original work 

 in some unexplored department of science, or in some 

 partly neglected corner, of which there are rtiariy in 

 every scientific field, however well cultivated. Like 

 the one-inch, the |- or the -g- will always be useful. 



As the observer's eye becomes better educated, 



