272 



THE AMERICAN MONTHLY [December, 



Griffith's Fine Adjustment. 



By E. H. GRIFFITH, 



FAIRPORT, N. Y. 



In Fig. I Nos. (i) (2) (3) represent the milled head, pinion-axis, 

 and pinion of the ordinary method of coarse adjustment. The milled 

 head (i) is countersunk on its inner side, and the small wheel (4) is 

 made to exactly ht the countersunk space, the inner svu^face of (i) and 

 of the wheel (4) being perfectly smooth and flat. Attached to (4) is 

 the socket and pinion (7), all of which are perfectly fitted over the pin- 

 ion-axis (2) between the pinion (7) and milled head (i). A leather 

 washer (5) is made to rest closely against the inner surfaces of (i) and 

 (4). It is held in position by another washer of metal (6) which, by 

 means of two screws passing through it and (5) is made fast to the 

 milled head. A small tension wheel (10) has a screw passing through 

 both washers, also binding them to (i), and when desired, locking the 

 coarse-adjustment bv making the whole combination practically one 



^_ 



Fig. I. 



wheel. When the coarse-adjustment is used, the spindle (S) holds (7), 

 (6), (5), (4), so that they cannot revolve with the pinion. When the 

 micrometer adjustment is required the friction of the leather washer 

 makes the whole combination practically one wheel, which is turned 

 by means of the milled head (S) , giving the entire range of the coarse- 

 adjustment for the fine adjustment. Both adjustments are always ready 

 for use when tlie tension wheel is properly set, except when the coarse- 

 adjustment is purposely locked to prevent accidents. All wear is taken 

 up by the spring. Fig. 3 shows the entire combination in position. 



In this combination of the two adjustments into one. but one groove 

 is required, greatly lessening the danger of lateral motion as in other 

 microscopes where two or more grooves are needed. The one groove 

 being close to the tube is another safeguard. 



