THE ROYAL ARTILLERY INSTITUTION. 
219 
With one exception the ranges decrease in a less ratio than the weights of 
the shell increase, indicating a less mean resistance to the heavier and slower 
shells, and proving an appreciable effect of resistance by the fact. On the 
mean of the five comparisons. 
0'962 ^i; 
the differences of weight ranging from 6 per cent, to 25 per cent. 
21. There is another criterion of the existence of an appreciable resist¬ 
ance afforded by the observed times of flight. If the resistance is nil, 
T = / Xtanft . 
v i 9 
and if it is appreciable, this quantity requires to be multiplied by a co¬ 
efficient (B) greater than unity, which has been computed by General Didion 
for all the cases which usually occur in practice.'* The observed times of 
flight are rather irregular, and present discrepancies which prevent our 
relying implicitly upon them. Thus we have t — 15 secs, for a range of 
1468 yds., and t = 16*8 secs, for a range of 1439 yds. at the same elevation. 
The former is certainly an error, perhaps for 16 secs. And on one occasion, 
when Professor Wheatstone's chronoscope was employed, it gave, on the 
mean of five good comparisons, a time of flight of 16*30 secs, as against 
16*95 secs, observed by the watch. Nevertheless, if we suppose the watch 
intervals uniformly 4 per cent, too long, there will still remain an appreciable 
retardation of the shells, due to the resistance of the air. 
Table IY. 
Observed Times of Flight compared with the Times due to the same 
Ranges in vacuo . 
Range 
X. 
0 
Observed time. 
D. 
Range 
X. 
0 
Observed time. 
D. 
/Xtancp 
v'TY 
/Xtancp 
By 
watch. 
By chro¬ 
noscope. 
B 7 
watch. 
By chro¬ 
noscope. 
V a 9' 
yds. 
degs. 
secs. 
secs. 
sees. 
yds. 
degs. 
secs. 
secs. 
900 
m 
13-0 
— 
13-73 
0-947 
1711 
48* 
19-0 
— 
18-98 
1-001 
1277 
48* 
17-0 
— 
16-40 
1-034 
1732 
48* 
20-0 
— 
19-10 
1-057 
1439 
42* 
16-8 
16-0 
15-68 
1-071 
2100 
45 
20-0 
— 
19-78 
1-011 
1468 
42* 
— 
16-1 
15-84 
— 
2120 
45 
21-5 
— 
19-99 
1-075 
1491 
42* 
16-1 
16-0 
15-96 
1-009 
2270 
48* 
24-0 
_ 
21-88 
1-097 
1525 
42* 
16-9 
16-6 
16-14 
1-047 
2323 
45 
21-0 
— 
20-81 
1-009 
1623 
42* 
17-3 
16-3 
16-65 
1-039 
2758 
45 
:24‘5 
— 
22-67 
1-081 
1681 
42* 
17-5 
16-6 
16-95 
1-032 
2759 
45 
23-0 
_ 
22-68 
1-014 
1700 
45 
17-75 
17-80 
0-998 
— 
— 
— 
— 
— 
T) = ratio of the observed time of flight to time in vacuo taken as unity. 
* See C[ Traifce do Ballistique,” Table XIII., or Table CXXXYIL of Captain W. H. Noble’s 
Second Report on Ballistics. 1865, 
