ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



649 



rectilinearly in the direction of the arrow on to the sensitive plate P in 

 the cassette C. The space in front of P is completely dark when V is 

 closed. For the purpose of long exposures V may be removed. When 

 the operator judges that the proper moment has arrived, he pulls a 

 lever at Gr, thus opening V and allowing the light to fall on the sensi- 

 tive plate at P. The author 

 adds a figure showing how 

 his apparatus is adapted to 

 Zeiss' large photomicrographic 

 camera. The space in front of 

 P is occupied by the bellows, 

 and the light-path from to M 

 has to equal that from to C. 



Fig. 112. 



(5) Microscopical Optics and. Manipulation. 



Simple Arrangement for determining Microscopically the Index of 

 Refraction.* — E. Clerici describes his method of carrying out a simple 

 mode of obtaining the refraction-index with an accuracy sufficient for 

 mineralogical and petrographic purposes. His method involves the use 

 of an object-slide fitted with a cylindrical cell, to the bottom of which 

 is fixed a small glass prism. A ray passed through this will, of course, 

 be refracted, and its duration can be measured by the cross-threads of 

 the ocular micrometer. If the cell be filled in succession with liquids 

 of known refractive indices, and a coverslip added, a curve can be con- 

 structed and the whole arrangement being thus calibrated is adapted for 

 the investigation of an unknown liquid. The author discusses the 

 advantages of several varieties of simple and compound prisms. 



Cheyroton L., and F. Vles.- 

 ultra-violette. 



-Examen de la striation musculaire en lumiere 

 C.R. Soc. Biol. Paris, lxvi. (1909) pp. 1057-9. 



(6) Miscellaneous. 



Telescopic Vision.t — Under the above title Johnston Stoney dis- 

 cusses the defects of the telescope, and inquires into the process by 



* Atti d. Reale Acad, dei Lincei, xviii. ser. 5 (1909) pp. 351-5 (6 figs.). 

 xvi. (1907) p. 336. t Phil. Mag., xvi. (1908) Aug., Nov., Dec. 



See also 



