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there will not be the least side motion and this 

 should be tested under the magnifying power of 

 an objective. There should be no sensation of the 

 individual teeth coming in contact. It is safe to 

 assume that if the rack and pinion shows either of 

 the above defects, the instrument is faulty in other 

 directions as well. 



Fine Adjustment. Nothing in the microscope 

 will cause more aggravation than a faulty fine 

 adjustment. It should work absolutely smooth 

 with no side play in the screw. The body should 

 respond promptly, when moving the milled head 

 rapidly forward and backward and should not 

 cause any swaying of the image during observa- 

 tion. The micrometer screw should be back of the 

 pinion, not at the front of the tube nor under the 

 stage. 



Metal. Whether an instrument shall be of 

 japanned iron or lacquered brass is probably 

 largely determined by the amount of money to be 

 expended. So far as the intrinsic suitability of 

 the metals is concerned there is no difference. 

 Brass however, offers a maker a better opportunity 

 for displaying his mechanical skill and while it is 

 no doubt true, that many highly finished instru- 

 ments are of poor workmanship in their working 

 parts, it is also a fact that a well made instrument 

 is always nicely finished. 



