THE MICROSCOPE. 27 



Mechanical Arrangements. The German and French 

 opticians devote their attention chiefly to the excellence 

 of their glasses, while the mechanical part of their instru- 

 ments is quite simple, not to say clumsy. They seem to 

 proceed on the principle that as little as possible should be 

 done by mechanism, which may be performed by the hand. 

 It is different with English and American makers, some 

 of whose instruments are the very perfection of mechan- 

 ical skill. The disparity in cost, however, for instruments 

 of equal optical power is quite considerable. 



Certain mechanical contrivances are essential to every 

 good instrument. The German and French stands are 

 usually vertical, but it is an advantage to have one which 

 can be inclined in any position from vertical to horizontal. 

 There should be steady and accurate, coarse and fine ad- 

 justments for focussing ; a large and firm stage with ledge, 

 etc., and with traversing motions, so as to follow an object 

 quickly, or readily bring it into the field of view ; also a 

 concave and plane mirror with universal joints, capable 

 of being brought nearer or farther from the stage, or of 

 being turned aside for oblique illumination. Steadiness, 

 or freedom from vibration, is of the utmost importance in 

 the construction, since every unequal vibration will be 

 magnified by the optical power of the instrument. 



Among so many excellent opticians it would be impos- 

 sible to give a complete list of names whose workmanship 

 is wholly reliable, yet among the foremost may be men- 

 tioned Tolles, of Boston ; Wales, of Fort Lee, N.J.', Gru- 

 now, of New York ; and Zentmayer, of Philadelphia ; 

 Powell & Leland, Ross and Smith, Beck & Beck, of London ; 

 Hartnack and Cachet, of Paris ; Merz, of Munich ; and 

 Gundlach, of Berlin. The optical performance of lenses 

 from these establishments is first class, and the mechanical 

 work of their various models good. The finest instru- 

 ments from these makers, with complete appliances, are 

 quite costly, except the Germans and French, whose ar- 



