308 MESSRS. R. H. FOWLER, E. G. GALLOP, C. N. H. LOOK AND H. W. RICHMOND: 
given on the assumption that the centre of gravity is 4*73 inches from the base in the 
3-inch shells used. The value of f R (at zero yaw) is also given for comparison. In 
fig. 5, the corresponding values of f M and f R are given for the shells of external 
fornTB,* the centre of gravity being supposed to be 4*965 inches from the base in the 
3-inch shells used. These values have been corrected as far as possible for the effect 
of the cards (see §2.32), and smooth curves have been drawn through the observations. 
The values of f ’ M and for shell A, and jf M for shell B, are given in the following 
table, Table I., for values of v/a varying by 0*1. These values have been read from 
the smooth curves of the figures. Besides f L , the value of / N , the force coefficient 
Curve I.—The moment coefficient / M (v/a) for 3-inch shells with a centre of gravity 4 • 965 inches 
from the base. 
Curve II.—The drag coefficient / E (v/a) shown roughly on ten times the scale. 
normal to the shell, is also given. These figures and Table I. represent the main 
results of the experiment. The values of f M have a probable error of less than 2 per 
cent., and the values of f L of about 10 per cent. 
The differences in the various curves for f u , f L and f M are very instructive. They 
show the complete impossibility of regarding the ratio of fu/fu, for example, as 
constant for large variations of v/a. Unlike f R ,fu is comparatively unaffected by the 
velocity of sound. It increases only to about 35 per cent, above its low velocity 
value, and does not maintain this increase except for a narrow range of velocities 
near v/a = 1. On the other hand f R increases to two and a-half times its low velocity 
value and maintains this increase. 
* See fig. 6. Form B may be specified thusLength 4 • 34 diameters. Base cylindrical. Head 
with an ogive of 6 diameters radius. Centre of gravity 1 • 655 diameters from base. 
