320 MESSRS. R. H. FOWLER, E. G. GALLOP, C. N. H. LOCK AND H. W. RICHMOND : 
The external form of the shells used in the trial is shown in fig. 6. It will be 
observed that at the junction of the body of the shell and the fuze or plug there is a 
distinct cutting edge of plan diameter 2-402 inches. It is clear, therefore, that when 
the impact takes place, a circle of cardboard, 2-40 inches in diameter, is punched out 
and cleanly removed by this edge ; the greater part of the circumference of this inner 
circle is usually removed by the subsequent passage of the body of the shell, which 
cuts the complete hole, but enough remains, in a bruised state, for yaws that are not 
A 
Direction of 
,nose of shell 
Fig. 8. Diagrammatic sketch of a typical hole, for a yaw between 1 degree and 4 degrees, when the 
velocity is low or medium. 
CCC. Inner circle—radius 240 inches, centre 0. 
ABA'B'. Outer circumference of hole. 
QQQ. Bruised part of card. 
AA'. Axis of symmetry or greatest diameter of hole. 
BA'B'. Circumference cut by teeth of driving band. 
BAB'. Ditto cut by nose or shoulder of shell. 
The lengths AA' (346 inches in figure) and OA' (l - 80 inches) each serve to determine the size of 
the yaw. 
The values of the yaw corresponding to the above values are 1 • 6 degrees and 1 • 8 degrees 
respectively, mean 1 • 7 degrees. 
too large, to define the position of the centre of this section of the shell at the 
moment of impact on the card. 
It follows, therefore, that there are two distinct methods by which the value of the 
yaw S can be determined. In the first place, there is a unique relation between the 
greatest diameter of the hole (AA', fig. 8) and the value of S ; secondly, there is a 
unique relation between OA' and S. These relations can be tabulated numerically 
when the plan dimensions of the shell are known, and the value of $ corresponding to 
any measured length AA' or OA' read off. 
