PRINCIPLES OP GUNNERY. 239 
described by its centre of gravity •”* but it was not until Professor 
Basbforth carried out a* series of systematic experiments with spherical 
and ogival-headed projectiles by means of his Clock Chronograph 
(1865 to 1870) that any accurate knowledge of the subject was 
obtained. A Committee of Reference appointed by the War Office, 
consisting of the Astronomer Royal, Professor Adams (Cambridge 
Observatory), Professor Stokes, of Cambridge, and Captain Andrew 
Noble, F.R.S., of Elswick, reported thus on these experiments:— 
“ The results showed that for moderate variations of velocity the 
resistance may be taken to vary as the cube of the velocity; yet for 
considerable variations of velocity this law no longer holds good; 
and that if for convenience the resistance be still represented by an 
expression of the form cv z , the coefficient c must be taken to vary 
continuously with the velocity. The experiments showed the values 
of the coefficient c of resistance corresponding to values of the 
velocity ranging from 850 to 1600 ft. per second. The coefficient 
is found to attain a maximum value for a velocity of about 1200 f.s. 
Professor Helie^s value of the coefficient of resistance is found to 
be true only for velocities in the neighbourhood of 950 f.s. The 
(cubic) law was stated by Professor Helie in his work published 
in 1865, and it appears to have been in use for some years before that 
time in the School of Artillery at Metz; but Professor Bashforth, 
without being aware of this, independently deduced the same law from 
his own experiments, so far at least as the ' law can be considered 
true—viz., for a limited range of velocity. Professor Bashforth, by 
his valuable experimental determination of the coefficient of resistance 
corresponding to different velocities, has furnished the data which are 
absolutely necessary in order to make the law applicable in practice.”*!* 
Bashfortffis method of experimenting consisted in observing the 
time of the passage of the same projectile through a series of succes¬ 
sive equal distances. J Previous experiments had measured only two 
intervals of time at each round, and in order to obtain the coefficient 
of resistance for different velocities, several rounds were fired with 
varying charges to get the required velocities; whereas Bashforth, 
by arranging 10 screens at intervals of 50 yds. apart, in one round 
determined the coefficient of resistance for a considerable variation 
of velocity—the velocity being gradually reduced in the distance of 
450 yds. by the resistance of the air. 
The Committee of Reference reported with regard to this point that 
e( there is a great advantage in being able to measure several conse¬ 
cutive intervals of time by the same instrument; since in this way 
each experiment supplies the means of testing the accuracy of the 
results, which are wholly wanting when only two intervals of time are 
measured, and that by two different instruments.” 
* Vide “ Traite de Balistique Experimentale,” p. 415. 
f Vide Report of the Committee of Reference (p. 160 of “ Reports on Experiments made 
with the Bashforth Chronograph.”) 
| Vide Bashforth’s “Motion of Projectiles,” p. 29. ^ 
Bashforth’s 
experi¬ 
ments. 
Report of 
Committee 
of Refer¬ 
ence on 
Bashforth’s 
experi¬ 
ments. 
Advantage 
of Bash- 
forth’s 
method of 
experi¬ 
menting. 
