ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



97 



Watson and Sons' New Mechanical Condenser Mount.* — In this 

 mount (fig. 10) a tube of the universal substage size is fixed below the 



;Fig. 16. 



iris-diaphragm, which can be carried by rackwork out of the optical 

 axis for obtaining effects when testing objectives for oblique illumination. 

 The apparatus includes also a rotating ring to carry dark-ground and 

 oblique light stops. 



Watson and- Sons' Aplanatic Low-power Condenser.! — This 

 condenser (fig. 17) is suitable for low and medium powers, up to a 

 numerical aperture of 0*65. It has a power of § in., and a numerical 



*\j^r 



Fig. 17. 



Fig. 18. 



aperture of 0*5, of which 0'48 is aplanatic. The diameter of the 

 back lens is 0*6 in. 



Watson and Sons' Macro-illuminator.^ — This is a single achromatic 

 combination of 1*25 in. clear aperture and 2 in. focus (fig. 18). It is 

 suitable for illuminating large objects under low powers. The lens is 

 mounted to fit into the substage close to the object, so as to focus the 

 image of the source of light on the objective. 



Watson and Sons' Catalogue, ISth edition, 1907-8, p. 98. 



t Loc. cit. 



t Loc. cit 

 Feb. 19th, 1908 



H 



