632 DE. E. EEANEXAJfD ON THE INELHENCE OF ATMOSPHEEIC PEESSUEE 
Comparing the amount of retardation with the corresponding reduction of pressure, we 
have the folio wmg results : — 
Numbers of experiments between 
which comparison is made. 
Diminution of ‘ ‘ 
pressure. 
Eetardation of 
combustion. 
inches. 
seconds. 
1 and 2 
2-86 
1-53 
2 and 3 
2-80 
T32 
3 and 4 
•97 
1'025 
Although these results, as I shall presently endeavour to show, are perfectly com- 
patible with those obtained with candles under similar circumstances, yet the subject 
seemed to me of sufficient technical importance to warrant a repetition and extension 
of these experiments in artificially rarefied air. For this purpose a large iron cylinder 
was connected on the one hand with an air-pump, and on the other with a piece of gas- 
pipe 6 feet long and 4 inches internal diameter, the opposite end of the pipe being 
furnished with an arrangement by which the end of the fuse to be ignited could be 
introduced air-tight within the pipe, whilst the closed end of the fuse projected about 
2 inches into the external air. The fuses were ignited at a given instant by a voltaic 
arrangement, consisting of ten cells of Geove’s battery, an instantaneous contact maker, 
and a piece of thin platinum wire which was inserted into the priming of the fuse. In 
order to ascertain with precision the moment when the deflagration was finished, the 
lateral hole at the posterior end of the fuse was bored through to the opposite side : a 
piece of thread was passed vertically through this aperture, and secured above to a 
convenient support, whilst an iron ball was affixed to its lower extremity at a distance 
of a few inches above an iron plate, upon which the ball fell when the fire reached the 
thread, thus indicating the moment when, under ordinary ch’cumstances, the fire of the 
fuse would be communicated to the contents of the shell. The pressure was indicated 
by a mercurial gauge inserted into the gas-pipe. 
The experiments were made with 6-inch fuses (for which I was indebted to the kind- 
ness of Mr. Abel of the Woolwich Eoyal Arsenal), in the following manner. The fuse 
being inserted into the end of the gas-pipe, and the necessary degree of exhaustion in 
the iron cylinder and pipe having been obtained, the fuse was ignited at a given signal. 
During the continuance of its deflagration, an assistant worked the air-pump so as to 
prevent any great rise in pressure, whilst another observed the vacuum-gauge at the 
moment when the u'on ball dropped. The mean between the pressure at the commence- 
ment of the deflagration, and that at the end, was assumed to be the mean pressure under 
which the fuse had been burnt ; but it is obvious that this assumed mean pressure can 
only be approximative, although the gauge fell very regularly and gradually during the 
continuance of the deflagration. 
The following results were obtained : — 
I. At a barometrical pressure of 30‘4 inches, fuse No. 1 burnt 31 seconds*. 
* The first three fuses were burnt in the open air, hut the arrangements for their ignition and for de- 
termining the cessation of combustion, were the same as in the other determinations. 
