nB Sir Humphry Davy on the combustion of 
even coal gas, or the contact of the same mixture with an 
extensive heated surface. An iron wire of of an inch and 
8 inches long red hot, when held perpendicularly in a stream 
of coal gas, did not inflame it, nor did a short wire of one sixth 
of an inch produce the effect held horizontally; but wire of the 
same size, when six inches of it were red hot, and when it was 
held perpendicularly in a bottle, containing an explosive mix- 
ture, so that heat was successively communicated to portions 
of the gas, produced its explosion. 
A certain degree of mechanical force which rapidly throws 
portions of cold explosive mixture upon flame, prevents 
explosions at the point of contact ; thus on pressing an explo- 
sive mixture of coal gas from a syringe, or a gum elastic 
bottle, it burns only at some distance from the aperture from 
W'hich it is disengaged. 
Taking all these circumstances into account, there appears 
no difficulty in explaining the combustion of explosive mix- 
tures within and not without the cylinders ; for a current is 
established from below upwards, and the hottest part of the 
cylinder is where the results of combustion, the water, car- 
bonic acid, or azote, which are not inflammable, pass out. 
The gas which enters is not sufficiently heated on the outside 
of the wire, to be exploded, and as the gases are no where 
confined, there can be no mechanical force pressing currents 
of flame towards the same point. 
It will be needless to enter into further illustrations of the 
theoretical part of the subject: and I shall conclude this Paper 
by stating, what I am sure will be gratifying to the Society, 
that the cylinder lamps have been tried in two of the most 
