362 



Mr. W. Galloway on the Influence 



[Mar. 2, 



the wick until the flame is only about an eighth of an inch high (that is 

 to say, until it has little or no yellow colour remaining), and observe 

 whether it has a " cap " above it or not. The cap is a spindle-shaped or 

 conical blue flame, more transparent than, and appearing to rest upon, 

 the oil-flame; it seems to be due to the combustion of that part of the 

 mixture of firedamp and air which becomes heated to the temperature at 

 which its active constituents can combine. It is known that when the 

 cap is large, there is much firedamp in the air; when it is small that 

 there is little ; and when there is no cap, it is almost, if not quite univer- 

 sally assumed that there is no firedamp present. 



There is not, however, so far as I know, any published information of 

 a definite kind concerning the appearances presented by the cap in mix- 

 tures of firedamp and air in different proportions; I have therefore 

 made a few experiments in order to obtain these data for the purposes 

 of this paper. The experiments were made on the 17th of January, in 

 the cabin near the bottom of the No. 3 Pit, Llwynypia Colliery. The 

 firedamp employed was from the same source as that with which the 

 coal-dust experiments were made, and was obtained from a pipe close to 

 the door of the cabin. The apparatus consisted of a measuring-cylinder, 

 a mixiDg-cylinder, a lamp, a bucket for holding water, and some india- 

 rubber tubes. The measuring-cylinder (fig. 4) is 10 inches long by 







2 inches in diameter ; it has a cock (a and b) in the middle at each end, 

 and a branch cock from each of these (c and d) ; it has also a water- 

 gauge a, opposite which there are marks and figures on the cylinder 

 showing the parts into which its volume can be divided. The mixing- 



