The old ancestral cannon-ball, fired as it was from a smooth-bore gun, had no means of acquiring this sudden longitudinal twist, and no sooner clear of the muzzle, it found itself involved in the performance of antics whimsical and capricious, turning over and over on its transverse axis, head over heels, side slipping, looping the loop. Again, the cannon-ball, being round, was limited in size to the bore of the gun, so that in addition to the disadvantage just mentioned of possessing no definite material degree of accuracy whilst on its headlong course through the air, it offered the further disadvantage of containing but a comparatively small explosive charge, and the air-resistance it afforded in proportion to its weight affected adversely, and in marked degree as compared with the modern longitudinal shell, its range and potential destructive energy. Reverting then to the modern projectile, and taking as a suitably illustrative example the 6-inch high-explosive shell (for it was on this particular type that Crewe was asked to concentrate), bearing always in mind, too, that the modern gun is rifled or grooved and that the effect of this grooving is to impart a vigorous longitudinal twist or spin to the shell as it flies away, making it gyroscopic and almost uniformly accurate, we notice that the length of this shell is eighteen inches, thus exceeding the diameter in the proportion of three to one, whence it becomes obvious that the capacity available for explosive charge is proportionately greater than that of a cannon-ball of the same diameter. We next find that in place of the rounded wind-resisting surface of the cannon-ball, the front end of the modern shell is pointed like a pencil, the atmospheric resistance being in this way reduced to a minimum. Decrease of wind-resistance naturally spells increase of range, and in this connection tests have in the past been carried out with shells having their bases as well as their noses pointed with a view to obviating the vacuum which is necessarily created by the usual flat base. A cigar-shaped shell, however, never proved satisfactory, for like the Rugby football it was decidedly wobbly in mid-air. How requisite was a superlative degree of accuracy and consequently of skill in the manufacture of the modern high-explosive projectile may, to some extent, be gathered from these briefly stated considerations, and will become more apparent still when we come to glance at the series of component parts of which the whole is built up.