CHAPTER IV. 



MANAGBMBNT OF THE MICROSCOPE. 



73. Support. — The Table on which the Microscope is placed, 

 when in use, should be one whose size enables it also to I'eceive 

 the various appurtenances which the observer finds it convenient 

 to have within his reach, and whose steadiness is such as to allow 

 of his arms being rested upon it without any yielding ; it should, 

 moreover, be so framed, as to be as free as possible from any 

 tendency to transmit the vibrations of the building or floor 

 whereon it stands.' The manner in which the Microscope itself 

 is constructed, however, will have a great influence on the efl'ect 

 of any such disturbing cause ; since, if the whole instrument 

 move together, scarcely any tremulousness will be produced in 

 the image, by vibrations which cause it to " dance" most un- 

 pleasantly, if the body and stage of the ^licroscope oscillate in- 

 dependently of each other. Hence, in choosing a Microscope, 

 it should always be subjected to this test, and should be unhesi- 

 tatingly rejected if the result be unfavorable. It is of course 

 to be borne in mind, that any vibration, either of the object or 

 of the optical apparatus, in which the other does not partake, 

 will be much more apparent Avhen high magnifying powers are 

 used, than when the object is amplified in a much less degree, 

 the motion of the object being magnified in precisely the same 

 ratio with the object itself; hence if, when the microscope is 

 thus tested with high powers, it is found to be free from fault, 

 its steadiness with low powers may be assumed ; but, on the 

 other hand, a Mici-oscope which may give an image free from 

 perceptible tremor when the lowest powers only are employed, 

 may be quite unfit for use with the highest. 



74. Light. — Whatever may be the purposes to which the Mi- 

 croscope is applied, it is a matter of the first importance to secure 

 a pure and. adequate illumination. There is scarcely any class 



' The working Microscopist will find it a matter of great convenience to liave a Table 

 specially set apart for this purpose ; furnished with drawers in which are contained the 

 various accessories he may require for the preparation and mounting of objects. If the 

 Microscope be one which is not very readily taken out from and put back into its case, 

 it is very convenient to cover it with a large bell-glass ; which may be so suspended 

 from the ceiling, by a cord carrying a counterpoise at its other end, as to be raised or 

 lowered with the least possible trouble, and to be entirely out of the way when the 

 Microscope is in use. Similar but smaller bell-glasses are also useful for the protection 

 of objects, which are in course of being examined or prepared, and which it is desirable 

 to seclude from dust. 



