J54* COMMON COAL. 
was, some years ago, adopted in the mines near White- 
haven and Workington, in which a wheel formed of 
steel, and in shape somewhat like that of a razor- 
grinder, was turned round with very rapid motion 
against a series of flints, and in such manner as to yield 
to the miners sufficient light to carry on their work in 
places where the flame of a candle would occasion the 
most dreadful explosions. Sir Humphrey Davy has 
lately invented, for the use of mines where this gas is 
prevalent, what is called a safety lamp. This is a lamp 
enclosed in a wire cylinder, the interstices of which are 
so extremely small as, whilst it gives light, will not ex- 
plode the gas. 
Another injurious exhalation in coal mines arises 
from the formation of carbonic acid gas, or fixed air 
(26), and is called choke damp. It is the property of 
inflammable air to rise to the upper parts ; but this, on 
account of its weight, occupies principally the lower 
parts of mines, and occasions death by suffocation, 
though it is by no means so fatal as the former. In 
some mines a prevention of injury arising from each of 
these gases is attained, by ascertaining the particular 
crevices in the coal from which they issue, confining 
them at those places within a narrow space^ and, if pos- 
sible, conveying them out of the mines, through long 
pipes, into the open air. 
There is yet another danger attending coal mines 
which requires to be provided against, and this is inun- 
dation. Many mines have been destroyed by the flood- 
ing of water, which springs up within them. The modes 
by which this was formerly extracted were extremely 
laborious, and, in numerous instances, entirely ineffica- 
cious. By means, however, of the fire or steam engines 
r.ow in use, the quantity of water raised from mines is 
perfectly astonishing. Four engines in one of the col- 
lieries at Whitehaven discharge more than twenty hogs- 
heads per minute, or upwards of 30.000 hogsheads in 
every twenty-four hours. 
The coal trade, which at present affords so important 
