THE EOYAL ARTILLERY INSTITUTION. 
261 
Second Group. 
Station. 
Altitude. 
Pressure. 
Mean time 
of 
burning. 
Mean 
irregularity. 
s. 
s. 
Ouchy. 
380 m. 
1246-77 Eng. ft. 
731 mm. 
28-78 in. 
9-15 
0-23 
St Pierre . 
1640 m. 
5380-74 Eng. ft. 
628 mm. 
24-724 in. 
10-12 
•29 
CHENA.LLETTES 
2890 m. 
9481 Eng. ft. 
538 mm. 
21-181 in. 
11-09 
•26 
It appears that in both cases the time of burning increases as the pressure 
diminishes. To determine the value of this variation between two specified 
pressures, it is only necessary to divide the increase of time by the whole 
time of burning at the higher pressure, and by the difference of the pressures. 
Thus will be obtained a coefficient which expresses the mean increase on 
unity of the time of burning (I s ) for a decrease of 1 mm. or *0394 in. of 
pressure. The fuzes of the first group were too irregular to allow of my 
using them for the calculation of this coefficient; those in the second group 
give the following values :— 
Between Ouchy and St Pierre .. 0-00104 
„ St Pierre and Chenallettes 0*00108 
These two coefficients which are nearly indentical show that the increase in 
the time of burning is proportional to the diminution in pressure. This 
very simple law has been already pointed out by Mr Prankland, 
To compare the values I have obtained with those of Messrs Mitchell and 
Prankland, it is only necessary to calculate by the aid of their results the 
coefficient (in millimetres) between the limits of pressure most nearly corre¬ 
sponding to those I have used. 
Taking the observations of Mr Mitchell in the Himalayas at the pressures 
of 752 and 584 millimetres, the coefficient is 0-00161; between 752 mm. 
and 609 mm. it is 0*00140. Thus the increase of time was a little greater 
with these fuzes. 
Amongst the six pressures which appear in the experiments of Mr Prankland, 
the two which agree most nearly with the limits I have used are the second 
716-8 mm. (28-189 in.) and the fourth 570*2 mm. (22*441 in.) 
Ml- Prankland has for the times of burning for these pressures 32*25 s. 
37-75 s. 
The coefficient from these results is 0-00116. Between Ouchy and 
Chenallettes my experiments give 0*00111. 
This agreement is very remarkable, and the more interesting because the 
fuzes used by Dr Prankland were different in size, form, and time of burning 
from those which furnished the results given above. 
[vol. III.] 
s 
