222 
POPULAR SCIENCE REVIEW. 
.actual temperature at any moment may be read off' without disturbing 
either of the others. The instrument is used at several meteorological 
stations in Switzerland and Russia, and gives great satisfaction. 
The Evaporation of Volatile Liquids . — The “ Philosophical Magazine,” 
No. 46, states that M. Stefan has lately conducted a series of researches on 
this subject. In the following experiments, to avoid the great lowering of 
the temperature at the surface, narrow tubes were chosen for evaporating 
vessels, instead of the wide vessels hitherto used ; with them he arrived at 
the following results : — (1.) The velocity of the evaporation of a liquid 
from a tube is inversely proportional to the distance of the level of the 
liquid from the open end of the tube. This law holds with rigorous exactness 
when the distance of the level a little exceeds 10 mm . (2.) The velocity of 
the evaporation is independent of the diameter of the tube. This result 
was obtained from experiments with tubes the diameter of which varied 
from 0 - 3 mm to 8 mm . (3.) The velocity of the evaporation increases with the 
temperature, so far as with this the vapour-pressure of the liquid rises. If 
p be the maximum of elasticity of the vapour corresponding to the tempera- 
ture of the observation, P the atmospheric pressure under which the liquid 
evaporates, the velocity of the evaporation is proportional to the logarithm 
of a fraction of which P is the numerator and P -p the denominator. If 
the pressure of the vapour becomes equal to that of the air, this logarithm 
becomes infinitely great, and signifies that under this condition the liquid 
bpils. 
Interruptions to the Atmosphere's Lower of Conducting Sound . — One of the 
most interesting and important papers that have appeared in that Journal 
for some years is that by Professor Tyndall on his experiments on the con- 
veyance of fog-signals (P.R.S. 149). It will be found in full at p. 175. 
Incandescent Substances Transmitting Electricity. — M. Donlot contributes a 
paper on this subject to the “ Comptes Rendus ” (December 22, 1874). He 
says that carbon and platinum act oppositely. Thus, a cylinder of glowing 
charcoal being substituted for the ball of an electroscope, if one bring near 
a positively charged body, the leaves will quickly diverge till they are dis- 
charged by the metallic balls on either side ; then diverge again, and be 
again discharged ; and so on, as long as the electrified body is held near. If 
it be removed before the leaves reach the balls, they remain apart, with 
positive electricity ; thus the carbon has allowed the negative electricity to 
flow off. The results are different where a negatively electrified body is 
used. The electroscope is affected only at a very small distance ; the leaves 
separate less quickly, and they come together promptly, whenever the source 
of electricity is withdrawn. These phenomena are quite opposite to those 
observed by M. Erman with the uphlogistic lamp — that is, with an incan- 
descent platinum wire — which indicate that incandescent platinum allows 
positive electricity to flow away more readily than negative. 
A Physical Society was much wanted in London, and now it is established. 
A numerously-attended meeting was held on Saturday, Feb. 14, 1874, in 
the Physical Laboratory at the Science Schools, South Kensington, for the 
purpose of establishing a Physical Society in London. The chair was 
taken by Dr. J. H. Gladstone. The bye-laws prepared by the Organising 
Committee appointed on Nov. 29 were received and amended. The fol- 
