204 THE USE OF THE MICROSCOPE 



the use of daylight glass (Gage) or tungsten-to-daylight 

 film (Wratten); the making of a special series of colored 

 glasses (Chance); and the improvements in electric hghts 

 which resulted in the C-Mazda, the tungsarc (or point of 

 light), and the 6- volt, thick coil or tungsten-ribbon lamp, 

 with pyrex glass. 



THE FUTURE OF THE MICROSCOPE 



This is of course speculation, and is no doubt tinged with 

 the individual preferences of the writer, even when he tries 

 to be impartial. 



Superfluities. — It is the writer's opinion, as already said, 

 that the following are, for the worker in biological matters 

 (including usually the bacteriologist), superfluous on the 

 modern standard microscope for high-power work: 



1. The Concave Mirror. — Petri dishes are probably best 

 examined with the Greenough, where the concave mirror 

 is useful. (The amplification of the Greenough has lately 

 been extended.) The concave mirror may then perhaps 

 well be omitted on the standard monocular microscope or 

 the monobjective binocular. 



2. The Uncorrected Condenser. — This is optically a relic 

 of the early days of Koch, nearly 50 years ago. It has been 

 retained, partly because its focus need not be changed 

 much, and partly no doubt because of the name of Abbe 

 which has somehow become attached to it, rather than to 

 his good achromatic condenser. The discovery that the 

 source of light must be small for the successful use of l-i or 

 %Q condenser cones, and that such cones give the best 

 representation of the object, apparently renders the uncor- 

 rected condenser an anachronism for high-power work. 



3. The Large Centering Suhstage. — This is intended to 

 correct the errors of centering of objectives and condensers. 

 Such errors in objectives on the nosepiece may be reduced 

 to a minimum by the opticians. Errors of importance in 

 centering of condensers and the sleeve of the substage 

 should not exist. For condensers with large lenses, special 

 centering may be not often needed; unless there has been 



