148 
MITCHELL: EXPLOSIVES USED IN MINING. 
should be provided for the workmen, so that they may be able to 
protect tliemselves from injuries from falls of roof and sides and other 
accidents of a similar nature, but the light must be at the same time 
so protected that it may be able to withstand an explosive atmosphere 
at a great velocity and to be self-extinguishing. 
The conclusion that the Midland Institute came to was, that a 
lamp of the Mueseler type, fitted with a "bonnet", was the most 
suitable. This type of lamp was tested under the direction of a Com- 
mittee especially appointed for the purpose at Aldwarke, and their 
conclusion was that gas could not be ignited outside this lamp at any 
velocity up to 3000 feet per minute, which was the maximum velocity 
attained. 
As no current in a mine in its ordinary course travelled at any 
such speed as 3000 feet per minute, it was clear they had arrived at 
something like a fair and proper safety lamp for the protection of the 
workmen, as against previous safety lamps. 
The next question to be considered was, how-to test the lamp prior 
its being sent into the mine? Some difficulty had arisen and some 
speculation as to the real safety of sending a lamp in without being 
properly tested, and several ingenious ways of testing had been sug- 
gested and tried, but I do not know of any so simple and practical as 
one that I have adopted at Mitchell Main Colliery, which is to place 
the lamp in a current of such a velocity as to exceed that of any 
current of air in the mine. This is done by means of an apparatus 
consisting of a long wooden tube with glass sides, and the current is 
created by a steam jet. In the apparatus several lamps can be tested 
at the same time. 
The reason I have adopted this system of testing is because in 
the various tests we found that if the flame was aff*ected to such 
an extent as to cause the light to flicker, we were able to explode it, 
but if the light of the lamp remained quiescent in a current of from 
23 to 26 feet per second it was safe for all ordinary purposes. The 
apparatus is very simple, and worthy the consideration of all colliery 
managers. 
The next thing the Committee dealt with was a very important 
one, viz. : — that of firing shots in mines. They had practically con- 
