of certain inflammable gaseous compounds. 25 
clean copper boiler, 2,5 inches deep and 5 inches diameter, 
slightly concave at bottom, capable of holding rather more 
than a quart of water, with an immersed thermometer, and a 
small vent for steam. It contained two pounds of distilled 
water, which was raised to the boiling point in similar times, 
namely, 20' by each of the flames ; so that it would appear, 
that to raise a quart of water from 50° to 212, 0 at 30 inches 
barometrical pressure, requires 
870 cubical inches of olefiant gas, 
1300 - - oil gas, 
2190 - - coal gas. 
From this experiment it may be inferred, that the air of a 
room equally lighted by oil and coal gas, will be much less 
heated by the former than the latter ; but that the actual 
heating power of the flames is in the direct ratio of the quan- 
tity of olefiant gas. 
9. Having occasion in some of the foregoing experiments 
to produce light of great brilliancy by the combustion of ole- 
fiant gas, and finding it very difficult to measure its intensity 
by a comparison of shadows, in the manner pointed out by 
Count Rumford, I endeavoured to avail myself of Mr. 
Leslie’s photometer ; for this purpose I concentrated the 
light by a plano-convex lens, and placed the blackened ball 
of the instrument in the focus. I found the effect, however, 
so great, as to lead me to believe that I had obtained a focus 
of considerable heating power, and on substituting a delicate 
mercurial thermometer, it rose 4°,5 in In the focus thus 
obtained from the light of a large Argand burner supplied 
with olefiant gas, the elevation of temperature was very sen- 
mdcccxx. E 
