-90 THE MICROSCOPE. 



The sub-stage, with its apparatus in place, can be 

 instantly removed, by being drawn out sideways, so as 

 to use the mirror alone, which is a great convenience. 



The mechanical movements of this instrument are 

 perfect, and well adapted to their purpose, and the 

 excellence of the workmanship is such as might have 

 been expected from the long-established reputation of 

 the house of Ross. 



The Ross-Zentmayer Student's Stand (fig. 46) is a useful 

 instrument on a small scale, possessing all the advan- 

 tages of a larger microscope. It has an excellent fine 

 adjustment, the milled-head for working which is in 

 as convenient a place as that of more expensive stands. 

 It is not so costly as more pretentious instruments, 

 .a consideration often of importance to the student of 

 the collateral sciences. Messrs. Ross make a very good 

 and cheap series of object-glasses for histological work, 

 especially adapted for use with this instrument. 



The general plan of Powell and Lealand's Compound 

 Microscope is represented in fig. 47. The tripod-stand 

 gives a firm support to the trunnions that carry the 

 tube to which the stage is attached, and from which a 

 triangular stem is raised by the rack-and- pinion move- 

 ment set in action by the double- milled head, whereby 

 the coarse adjustment of the focus is obtained. To 

 the upper part of the triangular bar a broad arm is 

 fixed, bearing the compound body ; this arm is hollow, 

 and contains the mechanism for the fine adjustment, 

 which is effected by turning the small milled-head. 

 The arm is connected with the triangular bar by a 

 strong conical pin, on which it turns, so that the 

 compound body may be moved aside from the stage 

 when necessary ; by a mechanical arrangement it 

 .stops when central. The stage has been improved in 

 construction, having vertical, horizontal, and circular 

 movements, and graduated for the purpose of register- 

 ing objects so as to be found at pleasure ; and in order 

 to do this effectually a clamping piece is provided 

 against which the object slide rests, and the circular 

 motion of the stage is stopped. It is an exceedingly 

 effectual method of finding a favourite object. The 



