ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



649 



mended tlia^t for any soap-bubble solution the ingredients be the best 

 and purest obtainable, and that chemically pure glycerin be used. 



Schafer's Hot-water Circulation Stage and Swift's Regulator. — 

 Prof. E. A. Schafer's hot stage (fig. 105), consists simply of a metal box with 

 a pipe at each end ; hot water entering by the lower end, and flowing 

 away at the upper. 



Messrs. Swift and Son use as a regulator for maintaining an even 

 temperature what is practically the same apparatus as was described in 



Fig 105 



this Journal, 1887, p. 316, a pipe for the gas leading into a tube with 

 mercury, whence it flows by another pipe to the gas-jet beneath the 

 water reservoir, the milled head screw regulating the height of the mercury 

 in the tube in the first instance. 



Bertrand's Refractometer.* — In order to measure the index of refrac- 

 tion of pyroxene, amphibole, &c., which is > 1-69 with this apparatus,! 

 M. E. Bertrand has made the hemispherical lens of flint glass {n = 1 • 962 ), 

 and proposes as moistening fluid methylen iodide (n = 1*75), the 

 refractive index of which might possibly be increased by dissolving 

 other substances in it. 



* Bull. Soc. Fran?. Min., x. (1887) pp. 140-1. 

 t See this Journal, 1887, p. 469. 



