64 
pose the tint in B darker than A. Take a white porcelain 
lid and elevate it or depress it in B until the tint produced 
is the same as in A, then if the height of the column of 
fluid above the disk be h, and the total length of the 
column H, and p the weight of the substance in A, then the 
weight in B will be . If the tint be stronger in A than 
h 
in B. then the disk must be allowed to sink in A until 
identity of tint is obtained. It will be convenient to have 
the cylinders of equal radii. If they are not so, then if R 
be the radius of B and r the radius of A, the quantity of 
R 2 H 
the substance sought in B will be —r, — p. Instead of sup- 
porting the string attached to the disk by the hand it 
would be more convenient for it to pass over a pulley and 
have a counterpoise at the other extremity 
“ On Explosions of Fire Damp/’ by Robert Raws on. Esq., 
Hon. Member of the Society. 
Mr. Binney has done wisely in calling the attention of 
the Society to the great loss of life in our coalmines by the 
explosion of light carburetted hydrogen. Surely the appli- 
cation of science may do a little good, even if its powers are 
limited to pointing out the advantages of order and obedi- 
ence while contending with a foe so subtle and powerful as 
is carburetted hydrogen, and which is unfortunately so 
plentiful in many of the coalmines® My object now is to 
supplement the excellent rules recommended by Mr. Binney 
with a few observations which struck me in reading Mr. 
Binney is paper on this subject. Fire damp may be regarded 
as an enemy possessing terrible powers — and coalminers on 
the other hand may be regarded as an army whose mission 
