ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



221 



whilst under examination, and the crystal-holder can be thrown out of 

 the field of view in order to fix the object to the wax. Made by Swift 

 and Son. 



Swift's Condenser for Illuminating Large Objects.* — This combina- 

 tion (fig. 32) is a modification of one of Swift's photographic lenses. It i& 



Fig. 32. 



1^^^ in. in diameter, with an approximate focus of 2 in., and is intended 

 for illuminating uniformly large objects under the lowest powers. The 

 illuminator is mounted in a similar way to the spot lens, and focuses^ 

 fairly close to the object. It is useful for photographing with Planars 

 or any short-focus photographing lens. 



Swift's Simple Hand Polarising Apparatus.f — This apparatus 

 (fig. 33) consists of an analysing and polarising prism, with one lens- 



Fig. 33. 



acting as a simple objective and another as convergent lens. The 

 instrument is constructed for estimating the thickness of sections of 

 minerals when being ground down to any given thickness previous to 

 finishing them off as microscopic sections, the thickness being ascertained 

 by polarising the mineral under observation. 



Herbert Smith Refractometer.| — The effective range of the refrac- 

 tometer (figs. 34, 35) is between 1 • 400 and 1 • 760, and the refractive 



* Swift and Sons' Special Catalogue, 1906, p. 50, fig. 55. 



t Tom. cit., p. 28, fig. 25. $ Tom.cit., p. 27, fig. 24. 



