46 



Modern Microscopy 



can be detected. The body should be racked up a consider- 

 able distance to see whether any rock or shake beyond that 

 of the tension on the bearings can be detected. An instru- 

 ment sound in construction should exhibit none whatever. 

 The stage should be treated in the same way. 



The next point is to ascertain that the body and limb 

 are perpendicular to the stage ; this should be tested with 

 a metal square, such as is generally used by brass workers, 

 engineers, and others, and can be purchased at a tool-shop. 

 If there be any inaccuracy in this respect it is important 

 that it be discovered before the microscope is used, other- 

 wise no objective can possibly work at its best. Eeference 



G F ^ 



Fig. 16. — Mechanical Stage showing the ' Spkung ' 

 WITH Adjusting Sokews. 



Fittings 



has already been made to the necessity for seeing that there 

 is no lateral movement in the fine adjustment and that the 

 sub-stage centres accurately. Beyond this it is well to put 

 a square between the upper surface of the sub-stage and 

 the under-side of the stage to ascertain that they are 

 parallel and that the sub-stage has been mounted with 

 accuracy. 



It is also of importance that each fitting in which move- 

 ments are effected should be provided with slots and screws, 

 by which the effects of wear and tear can be taken up. This 

 is known as ' springing ' the fittings, and the system is 

 shown very clearly in Pig. 16. Screws are placed at F and 

 G, which, on being tightened, produce a compression of the 

 fitting in which the slots are made, and wear can quickly 

 be adjusted for. 



