S06 
Numerous spiculae of sponges are also found, the most 
common of which are simple, smooth, and pointed at each 
end. Others are bulbed at one end and pointed at 
the other; sometimes of considerable length, but usually 
broken. I have also found one much branched, quadrifid, 
with two or more of the extremities bifid. 
In some sections I have observed fragments of a brown 
colour, apparently vegetable, and having a similar structure 
to portions of AlgcB, 
ON THE USE OF THE BAROMETER IN COAL MINES, AND A 
CHEAP FORM OF INSTRUMENT FOR THAT PURPOSE. 
, BY W. SYKES WARD, ESQ., F.C.S., OF LEEDS. 
Mr. Ward commenced by observing that he should not 
on that occasion attempt to discuss the necessity of 
using the barometer to prognosticate the state of the 
air in coal mines, as that had been proved in a paper 
by Mr. West. His object was to introduce the barometer 
to prevent accidents in mines. It is not the absolute 
height at which the barometer stands which will indicate 
danger, but the amount of diminution of pressure or 
rarefication of air which has taken place within a given 
time. Suppose the waste or goaf of a mine contain ten 
times the cubic capacity of the parts of the mine regularly 
worked and ventilated, if the barometer fall even as low as 
28 inches, so that it fall very gradually, the ventilation may 
carry away the carburetted hydrogen issuing from the goaf 
and fissures, and no danger be perceived. But if the 
barometer suddenly fall one-tenth of an inch, the gas in 
the goaf would expand one-hundredth part, throwing into 
the workings one-tenth of its volume, and producing an 
explosive mixture. To guard against that there should be 
a regular series of barometric observations taken in each 
