ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



457 



MICROSCOPY. 



A. Instruments, Accessories, &c* 

 CI) Stands. """ 



Draw-Tube Stop.f — S. Gelblum discusses the general conditions 

 which a draw- tube stop should fulfil ; he suggests the best practical 

 means for arriving at the result. He considers that, inasmuch as the 

 stop would have to be applicable to objectives of different lengths as 

 well as to preparations of different thicknesses, it would be best to 

 attach the stop to the objective itself. He recommends that the objec- 

 tive mount should be provided with a small cincture to which could be 



& 



:t ^; 



Fig. 61. 



attached a removable band of brass (fig. 64). From this band a small 

 arm terminating in a kind of button would project ; this button would, 

 on lowering the tube, come into contact with an adjustable button on 

 the stage, and so prevent the tube from being lowered beyond safety 

 distance. This stage button would, in reality, be the head of a screw 

 working in a small right-angled arm attached to the stage. The screw 

 could be adjusted at various heights, as required. 



Beck's London Penological Microscope.^— This instrument (fig. 65) 

 embodies the principle invented by Allan B. Dick,§ but numerous im- 



• This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 

 minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics 

 and Manipulation ; (6) Miscellaneous. 



f Zeitsehr. wies. Mikr.,xx. (1903) pp. 129-32 (3 figs.). 



t R. and J. Beck, Special Catalogue, 1904. 



§ See this Journal, 1889, p. 432, fig. 57. 



