884 CALORIFIC RELATIONS OF HYDROGEN AND OTHER GASES. 
«3. The temperature is also higher in this gas than in a vacuum ;- 
and the denser the gas employed, the higher the temperature. 
‘4. Hydrogen, therefore, conducts heat like a metal. 
«5. In all other gases the final temperature, as shown by an en- 
closed thermometer, is lower than in a vacuum; and the denser 
these gases become, the lower the temperature falls. 
«6. It must not be concluded from this, however, that the gases 
in question do not conduct heat at all ; but only that their powers of 
conduction are so feeble, as to be unable to overcome the opposition 
offered by their substance to the transmission of heat. 
«7. The striking conductibility of hydrogen is not only manifested 
when the gas is entirely free, so to say, within itself, but also when 
the enclosing vessel is filled with eider-down or other flocculent 
matters by which the free motion of the hydrogen is more or less 
hindered. 
«8, All gases, including hydrogen, offer a certain opposition to 
the passage of heat-rays; and the denser the gas, the greater this 
opposition. 
«9, Of all gases, atmospheric air, (and its constituents) offers the 
least opposition to the passage of heat. 
“10. The transmission of heat varies according to the source from 
which the heat comes. The rays which proceed from boiling water 
exhibit the greatest variation as regards their passage through 
different gases. 
“11. Of all colourless gases, Ammonia transmits the least heat. 
Next to this stands Olefiant gas. 
“12. The action of rays of heat, like those of light, may be in- 
creased by the employment of a tube. 
“13. The nature or condition of the inner surface of the tube 
affects the transmission of these rays. 
“14. The character of this surface changes also the conditions 
under which the rays are transmitted through different gases. 
“15. It follows consequently, that rays reflected from different sur- 
faces are transmitted through gases with different degrees of facility. 
“16. The rays transmitted from different sources of heat always 
pass through hydrogen gas with greater difficulty than through 
atmospheric air. 
“17. The high temperature indicated by a thermometer placed in. 
hydrogen gas into which heat is transmitted from above, does not. 
