Remarks on Oljections to Experiments on Vegetation. 213 
length must be joined to aa, reaching beyond the possible ex- 
tension of the flame. To prevent inflammation at the lower part 
of the fire, there must be only one aperture below the grate, into 
which an air-pipe must be closely fitted. This must extend 
above the top of the pit, and be of sufficient width to admit a 
free passage for the air downwards to the fire. By this means 
the remotest possibility of danger would be avoided either from 
a coke or a coal fire ; the rarefaction of the air would be depen- 
dent on the heated surface of the stove. 
I have ascertained by experiment, that a small current of pure 
hydrogen gas will inflame at the distance of nearly two inches 
above the apex of a newly-snuffed candle, but will not inflame 
when passed over the chimney of a lamp where paper would be 
scorched without ignition. We may by this means have a metre 
of the length of chimney necessary to prevent the inflammation 
of gas, according as the materials burned may evolve more or 
less flame. 
Where the apertures ee are used without the air-pipe, they 
may be covered with double wire-gauze, which might prevent 
any inflammation under the grate communicating with the air of 
the mine. With these precautions one or more fires might be con-_ 
stantly burning near the upcast shaft, and by increasing the 
quantity of heated surface, we may accelerate the ascent of air 
more rapidly than by an open fire as at present used, 
So long as the fire continues to burn, the air in the mine will 
never pass down the chimney or reach the fire from above; and 
were the hydrogen to inflame when the air is admitted through 
the apertures ee; if they are clothed with wire-gauze, the flame 
will be confined to the under part of the grate, and may be in- 
stantly extinguished by closing the apertures. 
The simplicity of this safety furnace will, J trust, recommend it 
to the early notice of coal proprietors; and should it be found to 
lessen the dangers to which the workmen in mines are exposed, 
my object in this communication to your valuable publication wil] 
be fully answered. 
I am, dear sir, yours, &c. 
13, Tavistock Street, Bedford Square, Rogt. BAKEWELL. 
Sept. 5, 1817. 
XXXV. Remarks on Mr. Murray’s Objections to Experiments 
on Vegetation detailed in the Phil. Mag. for July last. By 
Mr. J. Tatum. 
To Mr, Tilloch. 
Sir, — Your correspondent Mr. Murray has, in your last 
Number, objected not only to the manner in which I conducted 
03 the 
