386 Scientific Intelligence. 
rendering it heavier than the other ball. The wet ball was then 
more than ordinarily sensitive, while the other, which had become 
dry, was nearly insensible to heat. On removing the air, and so 
much of the vapor that the pressure was less than that due to the 
temperature, the balls became dry, and were no longer sensitive 
to the lamp, although still affected by the ice. When no vapor 
was present, the convection currents reigned supreme, even with 
very small pressures. 
These experiments seem to show that evaporation from a sur- 
face is attended with a force tending to drive the surface back, 
and D 
condensation with a force tending 
one second. In the case of mercury, this force will be only 6 lbs., 
but the latent heat of mercury being only one-thirtieth that of 
water, the same expenditure of heat would maintain nearly three 
times as great a force as in the case of water. In Prof. Crooke’s 
experiments the use of the Sprengel pump to produce a vacuum 
seems to account for the presence of a condensable vapor—PAil. 
Mag., xiviii, 146. a 
8. Index of Refraction of Liquids-MM. Terquem and Tran- 
NIN oo. a new method of determining the index of refraction 
of liquids, 
us and can 
With a Geissler tube containing hydrogen as a source of light, the 
: 3 a Hé. 
about half a minute, and for H¢ about a quarter of a minute. The 
measurements of several liquids are given, agreeing very closely 
a ee 
: 
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