260 
MINUTES OF PROCEEDINGS OF 
In order to avoid this source of error I used an electric machine for 
registering the duration of combustion. * 
The fuze was lighted by a pistol, the hammer of which in falling interrupted 
an electric current. 
The burning out of the fuze fired a small quantity of gunpowder, and the 
explosion caused the fall of a bar of metal, which re-established the electric 
current. 
The time of burning was thus noted on the register by the interval 
between two continuous currents ; this interval is easily expressed in time by 
a well-known process, which it is useless to explain. 
Some preliminary experiments were made to determine the degree of 
accuracy of which the method and the apparatus were capable. It appeared 
from these trials that the error could not exceed T V second. 
Two groups of fuzes were tried under five different pressures, varying 
from 730 millimetres (28*7411 in.) to 538 millimetres (21T811 in.). The 
fuzes were not so exactly similar as to give the same time of burning under 
the same pressure. 
To arrive at the influence exerted by the density of the atmosphere, 
it was necessary to burn a certain number of fuzes at the same station, and 
to take the mean time of burning; a comparison of these means should show 
the influence of the pressure. 
In order to neutralize as much as possible the difficulty arising from the 
want of regularity of the fuzes, the mean times of burning were taken at 
each station after eight or ten trials. Sixty-eight fuzes were burnt at five 
stations. 
The elevated point “ des Chenallettes ” just above the convent of St Bernard, 
9700 pieds above the level of the sea, is the highest station in the series. 
After some difficulty the instruments were set up on the rocky ridge which 
terminates this high point. 
The first group of fuzes were very irregular, the second less so. 
The means obtained were as follows :—■ 
First Group. 
Station. 
Altitude. 
Pressure. 
Mean time 
of 
burning. 
Mean 
irregularity. 
OlJCHY . 
380 m. 
728 mm. 
s. 
9-96 
0-52 
1246-77 Eng. ft. 
28-66 in. 
Gourze ...... 
920 m. 
3018-42 Eng. ft. 
685 mm. 
26-968 in. 
10-11 
•64 
St Pierre ... 
1640 m. 
5380-74 Eng. ft. 
628 mm. 
24-72 in. 
10-52 
•60 
St Bernard 
2478 m. 
8130- Eng. ft. 
568 mm. 
22-363 in. 
11-20 
•55 
