ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



807 



foruse with all kinds of illumination — polarized light, dark-ground, ultra- 

 microscopy. 



Among instruments which have to some extent anticipated his re- 

 quirements, the author mentions the Wenham-Schroeden objective- 

 prism, made some fifteen years ago by Ross of London, under the title of 

 " Improved Binocular Prism for High Powers." The excellent qualities 

 of this prism — which he fully enumerates — are counterbalanced by the 

 ponderous stand, which makes a rather unwieldy and costly instrument. 

 In conclusion, while admitting that for certain special purposes, e.g. 

 resolution of more difficult structures, test-objects, and so forth, the 

 monocular instrument is the more suit- 

 able, yet for most systematic purposes, 

 and especially for prolonged observa- 

 tions, he thinks that the binocular is 

 so much to be preferred that he hopes 

 his suggestions will not be unattain- 

 able. 



Comparator or Reading Micro- 

 scope.* — This instrument (figs. 87, 88), 

 made by the Cambridge Scientific 

 Instrument Company, can be used 

 with the axis of the Microscope 

 vertical, horizontal, or inclined. The 

 illustration (fig. 87) shows it with 

 the axis vertical ; in fig. 88 it is seen 

 as a cathetometer, with the Microscope 

 horizontal. The tube B, to which 

 the Microscope is clamped, can be 

 traversed slowly by the screw and 

 milled-head S through 40 mm. read- 

 ing, being taken on the divided 

 micrometer-head to 0*01 mm. For 

 supporting the object under examina- 

 tion a small sliding table I, resting 

 on geometric fittings, is provided. 

 This is supported with centring adjustments controlled by the screws F, F. 

 Lucas's patent slow motion is used for this focusing mechanism of the 

 Microscope. The Microscope M, which is fitted with cross lines and can 

 be clamped at any point on the tube B, has a Zeiss achromatic objec- 

 tive a. 2 and No. 2 ocular. The working distance between the nose of the 

 objective and the object is 30 mm. The instrument, which weighs 

 17 lbs., is used as seen in fig. 87 for the examination of screws ; it is 

 also employed for measuring the hardness of steel. This is done by 

 pressing a small steel ball into the steel to be examined, by the pressure of 

 a known weight. The indentation thus produced is a measure of the 

 hardness, the diameter of the indentation being measured by the Micro- 

 scope. 



* Cambridge Scientific Instrument Co., List No. 88, p. 9 (2 figs.). 



Fig. 



