UPON SOJIE OF THE PHENOMENA OE COIklBHSTION. 
631 
These numbers give the following average rates of combustion : — 
At Chamonix 9 ’6 grms. stearin per hour. 
Summit of Mont Blanc 9T grms. stearin per hour. 
Or, omitting the fourth candle, which obviously gave abnormal results, the following 
would be the average rate of combustion : — 
At Chamonix 9-4 grms. stearin per hour. 
Summit of Mont Blanc 9-2 grms. stearin per hour. 
This close approximation of the two results under such widely different atmospheric 
pressure, goes far to prove that the rate of combustion of candles is entirely indepen- 
dent of the density of tlie air^ the slight discrepancy being probably attributable to the 
difference (21° C.) of atmospheric temperature in the two series of experiments. It is 
impossible to repeat these determinations in a satisfactory manner with artificially rarefied 
atmospheres, owing to the heating of the apparatus which surrounds the candle, and the 
consequent guttering and unequal combustion of the latter. But in an experiment with 
a sperm candle, which was burnt first in air under a pressure of 28'7 inches of mercury, 
and then in air at 9 inches pressure, other conditions being as similar as practicable in 
the two experiments, the consumption of sperm was found to be, — 
At pressure of 28-7 inches .... 7'85 grammes of sperm per hour. 
At pressure of 9'0 inches . . . . 9T0 grammes of sperm per hour. 
This experiment, unsatisfactory as it w’as in several respects, tends to confirm, for 
higher degrees of rarefaction, the result previously obtained. 
(3. Of Timefuses. 
In a letter dated January 6th, 1855, an extract from which appeared in the ‘Proceedings 
of the Boyal Society Quartermaster Mitchell communicated the results of a series of 
carefully conducted experiments, proving that the rate of combustion of the fuses of shells 
was subject to considerable retardation, which he attributed to the diminution of atmo- 
spheric pressure at elevated stations, causing a more scanty supply of oxygen. The 
following is a short statement of the results of these experiments, in which three-inch 
fuses were burnt under different atmospheric pressures ; — 
Height of barometer 
at 0® C. 
Elevation above 
sea-level. 
Time of burning. 
inches. 
feet. 
seconds. 
1. Average of G experiments . . 
29-61 
14-25 
2 Average of 6 experiments . . 
26-75 
3000 
15-78 
3 Average of 4 experiments . . 
23-95 
6500 
1710 
4 Average of 2 experiments . . 
22-98 
7300 
18-125 
* Vol. vii. p. 316. 
