Sir H. Davy's researches on flame. 6 1 
/ a 
Olefiant gas - - - 1.15 
Coal gas - -55 
Azote - 1.30 
Oxygene - - 147 
^Nitrous oxide - - 2.30. 2.33 
^Carbonic acid gas - 2.45 
Chlorine - 3.6 
It appears from these experiments, that the powers of 
elastic fluids to abstract or conduct away heat from solid sur- 
faces, is in some inverse ratio to their density, and that there 
is something in the constitution of the light gases, which 
enables them to carry off heat from solid surfaces in a diffe- 
rent manner from that in which they would abstract it in 
gaseous mixtures, depending probably upon the mobility of 
their parts.-f The heating of gaseous media by the contact 
of fluid or solid bodies, as has been shown by Count Rum- 
ford, depends principally upon the change of place of their 
particles ; and it is evident from the results stated in the 
beginning of this section, that these particles have different 
powers of abstracting heat analogous to the different powers 
of solids and fluids. Where an elastic fluid exerts a cooling 
influence on a solid surface, the effect must depend princi- 
pally upon the rapidity with which its particles change their 
places : but where the cooling particles are mixed throughout 
a mass with other gaseous particles, their effect must princi- 
* These two last results were observed byMr. Faraday of the Royal Institution, 
(from whom I receive much useful assistance in most of my experiments), when I was 
absent from the Laboratory. 
+ Those particles which are lighest must be conceived most capable of changing 
place, and would therefore cool solid surfaces most rapidly : in the cooling of gaseous 
mixtures, the mobility of the particles can be of little consequence. 
