PHYSICS: C. G. ABBOT 
387 
projectile a plurality of bell-shaped bores were provided, leading tangen- 
tially from the chamber within the projectile to the rear where they 
emerged into the barrel of the gun. On screwing the aluminum nose 
with its steel boss into the opening of the chamber the whole presented 
the appearance of an ordinary elongated projectile except for the bell- 
mouthed bores visible at the rear. When the gun is fired the propellant 
within the chamber is ignited by priming contained in the tangential 
apertures. 
The outflow of the gases through the bell-mouthed bores, while they 
would give some rotation, owing to their friction within the chamber, 
would fail to give sufficient rotation if it were not that steel pins are 
inserted across the chamber to form a sort of bafHe, so that the outflowing 
gases may react against this baffle and so tend more strongly to rotate 
the projectile. 
It was feared that the combustion would not be completed, or at least 
that the gases would still remain in the chamber at high condensation 
at the time when the projectile left the muzzle of the gun. If this were 
the case it might easily be that owing to some slightly unsymmetrical 
construction of the bell-mouthed bores some tendency to deflect the flight 
of the projectile would be caused thereby by the delayed outrush of the 
residue of gases. In order to avoid this, the end of the barrel was con- 
tinued by a tube extending some 10 inches beyond the former muzzle and 
at the rear of the tube where it joined the barrel there were drilled a 
number of holes so that the gases might escape therefrom, and relieve the 
pressure within the chamber of the projectile while still it was subject 
to guidance from the lengthened barrel of the gun. 
Very satisfactory results have been obtained in firing these special 
projectiles. This method of securing rotation of projectiles appears to 
be suitable not only for trench warfare but for all varieties of ordnance 
larger than 1 inch in diameter. Rotations as great as one rotation in 
18 caHbers have been obtained thereby. It is customary to employ 
about one rotation in 30 calibers in the ordnance of Europe. The United 
States employs one rotation in 25 calibers for a large number of its heavy 
guns. My experiments seem to show that one rotation in 40 or 50 
caHbers is sufficient to prevent any appreciable deflection of the shells 
in flight. 
The experiments have been conducted within the enclosure of the 
Astrophysical Observatory, so that it was impracticable to employ heavy 
charges so as to get very high speeds of flight, but within the range of 
the experiments I have found by shooting through a succession of paper 
screens and observing the holes with a theodoKte that within the length 
