Microscopes of Powell, Boss, and Smith. By E. M. Nelson. 429 



Piccadilly, and in 1839 the article "Microscope" in the Penny 

 Cyclopaedia, written by him, was published. In this article is figured 

 a simplified form of Valentine's Dissecting Microscope, fig. 109. It 

 has no fine adjustment, but as there is a thoroughly well sprung 

 rackwork coarse adjustment acting upon a triangular bar, its focussing 



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Fig. 110. 



a a 



Fig. 111. 



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V/WWWWWA 



Fig. 112. 



capabilities are quite equal to the work it is intended to perform. The 

 springing of the coarse adjustment pinion of this Microscope was 

 an advance upon that of Valentine ; for while Valentine's was like 

 fig. 110, this Microscope had one like fig. 111. This kind of sprung 

 coarse adjustment was first used in 0. Varley's Vial Microscope, made 

 by Hugh Powell in 1833, and it is even 

 now by far the best method of mount- 

 ing the pinion ; but it has been given up 

 by all manufacturers except Powell. 

 This instrument is very portable, for 

 the pillar unscrews from the foot, the 

 mirror unships, and the two screws 

 seen at the back liberate the stage, 

 which can be packed flat in the case. 

 This Microscope is also figured in vol. 

 iii. p. 220 of the Quarterly Journal of 

 Microscopical Science (1855). 



The next Microscope, a compound, 

 fig. 112, is also figured in the Penny 

 Cyclopaedia. The foot and pillar are 

 similar to those of the dissecting stand, 

 but the feature that at once attracts 

 attention is the Lister limb supporting 

 a cradle which carries the body. It 

 has been thought that this form of 

 mount was suggested by Mr. G. Jack- 

 son ; but we learn, from a note in the 

 Quarterly Journal of Microscopical 



Science,* that the editors have Mr. Jackson's authority for saying that 

 it was originally made by Mr. Eoss. The fine adjustment is of the 

 short lever nose-piece type. Although the name of the inventor of 

 this kind of fine adjustment is not stated, it is pretty certain that it 

 was Andrew Ross. James Smith fitted a somewhat similar arrange- 

 ment to one of his early Microscopes in 1839. 



The stage is mecha- 



Aug. 15th, 1900 



Vol. i. p. 219 (1853). 



2 G 



