198 Till: HISTORY AND DEVELOPMENT OF THE MICEOSCOPE 



ment being slowei 



which \v;is without arrangement for rotation; and the mirror was 

 not. jointed. The model of T. Ross had, as will be seen, a bar move- 

 n ii -nt, with a foot formed of a triangular plate to which were bolted 

 two parallel upright plates to carry the trunnions of the microscope. 

 Tin- fine adjustment is a lever of the second order, with the milled 

 head in the middle of the bar, which involves tremor, and the tube of 

 the nose-piece is short, making shake possible. 



The stage movements are of unequal speed, the lateral move- 

 fhan the vertical. There is no finder, and the 



rotation of the stage is 

 but partial. The sub- 

 stage and mirror are 

 good. It was a com- 

 manding instrument in 

 its day, and was of ex- 

 cellent workmanship 

 and finish ; but it was 

 not equal to the strain 

 of critical work with im- 

 mersion objectives of 

 great aperture. Xe'Ver- 

 theless the defects of this 

 stand could have been 

 readily corrected . "\V i T 1 1 

 a more extended ba.se. a 

 better arrangement of 

 the fine adjustment, a 

 mechanical stage con- 

 structed on better prin- 

 ciples, and the rotation 

 made complete and con 

 centric which it was 

 not this would have 

 been, even for our pre- 

 sent requirements, an 

 a d 1 1 1 irable instrument . 



This important firm 

 were otherwise advised, 

 however ; and, instead 

 PIG. 160. -Ross-Zentmayer model (1878). *!" of correcting the error* 



of the instrument whose 



they had made, they designed an entirely neir, model in which 

 a Lister limb was substituted tor the bar movement, Fig. lb'0 illus- 



I|M ~ r " r fthe instrument, from which it will be seen thatthe 



also was changed for the worse ; the base was not sufficiently 



the hinder part of the font u as too large, so that it 



times rocked on four points, because the hinder part was too 



surface, in fact. A true tripod will stand firm on an 



ible,bu1 this form will not. It is a form liv(|ii-ntly used by 



- and is known as the 'benl daw.' It'is a bad 



be, as it has been, easily thrown over laterally. It 



