112 



SUMMARY OF CUEEENT EESEAECHE8 EELATING TO 



to penetrate to the object or be of use for illumination. Still, 

 again, experience seems to prove very conclusively that the most 

 effective as well as the simplest arrangement for securing oblique 

 light (otherwise than from the mirror alone) is by the prism, the 

 traverse lens, the Wenham ' half button,' or other immersion sub- 

 stage illuminators. These considerations lead strongly to the 

 conclusion that the swinging of the substage is useless." 



Ranvier's Microscope-Lamp.* — This (Fig. 21) is described as 

 consisting essentially of a metal globe, which covers the cobalt glass 

 lamp chimney " and prevents the radiation of heat." Four openings 

 with plano-convex lenses conduct the light to four Microscopes. 

 " The light can be so subdued that it is possible to work a long time 



Fig. 21. 



in the evening without straining the eyes, for which reason the lamp 

 is preferable to all other kinds of illuminating apparatus. The 

 cobalt glass is an essential feature, because the yellow-colour of the 

 lamp-light is thereby obviated, and the sensation of white is produced. 

 Certiin shades of yellow and blue, as is well known, stand in 

 relationship to each other as complementary colours, that is they 

 produce white." 



Hollow Glass Sphere as a Condenser, f — Mr. F. Eitton describes 

 the effects of using a glass globe filled with water for the purpose of 

 condensing light upon the object. This was used by some of the early 

 microscopistsjj though it appears soon to have fallen into disuse, as it 



* Thanhoffer's ' Das Mlkroskop und seine Anwendung,' 1880, pp. 73-4 (1 fig.), 

 t Sci.-Gossip, 1881, pp. 274-5 (1 fig.). 



X Hooke, ' Micrographia,' 1665 ; Ledermiiller, ' Mikroskopische Gemiitbs- und 

 Augen-Ergozung,' 1762. 



I 



