4 ,6 *SVr H. Davy’s researches on flame. 
treat of my subjects under four heads. In the first I shall 
discuss the effects of rarefaction, by partly removing the 
pressure of the atmosphere upon flame and explosion. In 
the second, I shall consider the effects of heat in combustion. 
In the third, I shall examine the effect of the mixture of 
gaseous substances not concerned in combustion upon flame 
and explosion. In the fourth, I shall offer some general views 
upon flame, and point out certain practical and theoretical 
applications of the results. 
I. On the effect of rarefaction by partly removing the pressure , of 
the atmosphere upojifla?ne and explosion. 
The earlier experimenters upon the Boylean vacuum ob- 
served that flame ceased in highly rarefied air: but the 
degree of rarefaction necessary for this effect, has been diffe- 
rently stated. Amongst late experimenters, M. de Grotthus 
has examined this subject. He has asserted that a mixture 
of oxygene and hydrogene ceases to be explosive by the elec- 
trical spark when rarefied sixteen times, and that a mixture 
of chlorine and hydrogene cannot be exploded when rarefied 
only six times, and he generalises by supposing that rare- 
faction, whether produced by removing pressure or by heat, 
has the same effect. . 
I shall not begin by discussing the experiments of this 
ingenious author. My own results and conclusions are very 
different from his ; and the cause of this difference, will I 
think be obvious in the course of these inquiries. I shall pro- 
ceed in stating the observations which guided my researches. 
When hydrogene gas slowly produced from a proper mix- 
ture was inflamed at a fine orifice of a glass tube, as in the 
