OP THE MICBOSCOPE. 95 



ON THE SELECTION OF A MICROSCOPE FOE PRAC- 

 TICAL PURPOSES. 



The object of all the information given in the preceding 

 pages, is to enable the reader not only to understand the con- 

 struction of the microscope, but to select one judiciously ; and, 

 therefore, in every section we have offered hints bearing in this 

 direction. We now propose to give the reader such special in- 

 structions in regard to the choice of an instrument as are 

 necessary in addition to those previously offered. 



Those who will examine the catalogues of the various makers 

 of microscopes, will find the instruments divided into first, 

 second, third, fourth, etc., classes, the microscopes in each 

 succeeding class in this descending scale being smaller and less 

 complete than those in the one preceding it. The first-class 

 microscopes of almost all our prominent makers are large, 

 beautifully-made instruments. They are provided with me- 

 chanical movements in every part, whereby the utmost delicacy 

 and precision in making an adjustment, and in recording it, 

 may be obtained, and as a natural consequence, such instru- 

 ments are quite expensive. Indeed, it will often be found that 

 the hanging and adjustment of the mirrors alone, of these fine 

 stands, cost as much as an entire microscope of the lower 

 grades. 



Second-class stands are usually smaller than those of the first 

 class, but they are frequently very complete as regards their 

 adjustments and arrangements. Microscopes of the third and 

 fourth class are usually much simpler in their construction, as 

 well as less in size. In addition to these different classes, most 

 manufacturers offer models adapted to special purposes, so that 

 in setting out to procure a microscope, the beginner is very apt 

 to be bewildered unless he has the guidance of some judicious 

 friend. Of course those who are mere dealers always urge the 

 purchase of the most complete and expensive microscope which 

 the funds of the purchaser will enable him to procure, whereas 



