Physics and Chemistry. 105 
9. Of all gases, atmospheric air or its constituents conduct heat most 
perfectly. 
10. The passage of heat is different according to the source from which 
it comes. The rays emitted by boiling _— exhibit the greatest differ- 
iy in their passage through different 
f all colorless gases, ammonia joanna te the least heat; after this 
clefiant gas, 
the application of a tube, the action of the rays of heat can be 
increased like that of rays o 
he character of the walls of the containing vessel changes the 
oo in which rays of heat pass through the gases contained in 
ube. 
he character of the — also changes the proportion in which 
she, rays pass through differen 
. From this, it cong. om. rays s reflected from different surfaces are 
transmitted by gases, with different degrees of facilit 
6. ee, rogen aay erenics rays from different sources of heat, 
in hydrogen mn Ww e gas is s heated from above, does not 
therefore depend upon a “greater capacity of transmission but only on a 
greater conducting pow 
18. The greater conducting power of hydrogen for heat si ag a new 
Teens in favor of the analogy of this substance to the Is 
9. Hydrogen also conducts electricity better than the ‘lik gases.— 
P ae Ann., exii, 351. Ww. G. 
2. Ona new Unit of Electrical Resistance —MartiessEN propose 
employ as a unit of resistance in electrical measurements, the anes 
of a wire composed of two parts by weight of gold and one part of silver, 
having a length of one meter and a thickness of one millimeter. The 
author shows that this alloy conducts electricity with almost equal facility 
at different temperatures between 0° and 100°, that small quantities of 
pe ag do not sensibly affect its conducting’ power, and that the an- 
nealing of the metal is ‘also without sensible influence. The memoir 
contains empirical formulas by which the small differences in conducting 
power occasioned by v ariations in temperature m ay be taken into ac- 
1, with an adjustable slit for the 
other grates of the 
