553 
The rise of the indicator is noted and compared with a 
table giving the per centage of coal-gas. If we have to 
determine carbonic acid, the fall of the indicator is compared 
with another table to ascertain the per centage present. 
The following results have been obtained in the presence 
of experienced miners by the aneroid indicator : — 
The aneroid indicated 1*5 per cent, of fire-damp. The 
Davy lamp gave no indication. 
The aneroid indicated 3*0 per cent, of fire-damp. The 
gas could be detected by the Davy lamp, which gave a small 
pale blue cap of flame. 
The aneroid indicated 6*0 per cent. The Davy lamp did 
not explode, but its flame elongated greatly. 
The aneroid indicated 8*0 per cent. The Davy lamp 
exploded feebly. 
The aneroid indicated 10*0 per cent. The Davy lamp 
exploded fiercely. 
In the words of a competent critic, "It is impossible to 
conceive a more refined application of science than this, nor 
one that will be found of greater practical utility, as indi- 
cating the presence of fire-damp in collieries, before it becomes 
dangerous from accumulation." 
In a short discussion which followed the reading of the 
communication, 
Mr. Briggs, of Outwood Hall, said the instrument showed 
very readily the quantity of gas which might be present in a 
coal mine. Davy's lamp was sometimes called a safety lamp, 
but it was not a safety lamp. It did not indicate the presence 
of gas. Stephenson's was a safety lamp, because the light 
went out when the gas got to a certain point, and the men 
were then warned to leave their work. Stephenson's lamp was 
rather more expensive than the other. Many of the accidents 
in pits were caused by the improper and careless conduct of the 
