54 ON THE FIRE-DAMP OF COAL-MINES, 
opening in the form of a short tube. The heat of the air is- 
suing from an aperture of this size, with a flame such as has 
been described, I found to be 370°, the bulb of the thermome- 
ter being in the current exactly at the orifice ; when introdu- 
ced entirely within the aperture, and immediately above the 
flame, it rose to 465°. Air of this temperature, it is obvious, 
cannot inflame fire-damp, or any mixture of it. 
No very accurate adjustment is required with regard to the 
size of the tube conveying the air into the lantern. It is suf- 
ficient to have it wide enough; the state of the flame is then 
regulated entirely by the size of the upper aperture, and any 
slight excess of width in the tube beneath is of no importance. 
I find that with a lantern and lamp of the above size, a tube 
‘three-fourths of an inch in diameter interior measure, and three 
feet and a half in length, answers very well. This circum- 
stance, of no accurate adjustment being necessary, gives an ad- 
vantage to this method in actual use. Where the safety of the 
lamp depends on such an adjustment, it is difficult to construct 
it in such a manner that it shall burn with a bright flame, and 
steadily, so as not to be liable to be extinguished by move- 
ment, or by the least failure either in the current of air, or in 
its purity. The bringing the air from the floor renders any 
such adjustment unnecessary, and allows, therefore, of a more 
bright and steady flame being produced with entire safety. 
And by the lamp being thus always supplied with the purest 
part of the air, it will continue to burn where any safety-lamp 
on a different principle must be extinguished, and of course 
will enable the miner to work in situations where no other will 
be of any use. 
In fixed lamps, the length of the tube must be regulated by 
the height of the passages. The thickness of the two beds of 
coal at Newcastle is about six feet each. But it is unequal, 
and. 
