242 
CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER, 
factor ‘84. Again, with, the 11-inch gun, when the still larger charge of 235 lb. was 
employed, it will be found from the figures above given that the factor of effect for 
this gun, powder, and charge is about '89. 
Hence the factor of effect with the same powder has gradually increased from about 
'83 in the powder-proof gun, to '84 in the 8-inch gun, to *86 in the 10-inch, and to 
•8.9 in the 11-inch gun. And generally we must point out that not only may the 
factors of effect differ very much with the powders employed, being in this respect 
dependent upon circumstances, such as the density of the powder, its size of grain, 
amount of moisture, chemical composition, nature of charcoal used, &c., but they 
may also vary considerably even with the same powder if the charges be not fired 
under precisely the same circumstances. For example, especially with slow-burning 
powders, the weight of the shot fired exerts a very material influence upon the factor 
of effect, and the reason is obvious : the slower the shot moves at first the earlier in 
its passage up the bore is the charge entirely consumed and the higher is the energy 
realised. The same effect, unless modified by other circumstances, is produced when 
the charge is increased with the same weight of projectile. In this case the projectile 
has to traverse a greater length of bore before the same relief due to expansion is 
attained. The higher pressures which consequently rule react upon the rate of com¬ 
bustion of the powder, and again a somewhat higher energy is obtained. 
But these increased effects, of course, correspond to an increased initial tension of 
the powder gases; but, especially with the smaller guns, a very great difference in the 
realised energy may arise from other causes. Thus, it having been found that with 
certain breechloading guns a superior effect was attained by substituting copper 
rings for lead coating, it was assumed that the cause of this superiority was due to 
the less friction of the copper rings in the passage of the shot up the bore. But it 
occurred to one of us that the superior eflect was in all jwobability not due to less 
friction, and the following experiments were made. 
Three rounds were fired from a 12-centhnetre B. L. gun with 7 lb. B. L. G. powder 
and the ordinary service lead-coated shot. The energy realised per lb. of powder was 
80'65 foot-tons. 
Three more rounds were fired with the lead considerably reduced, and so as barely 
to fill the grooves. The mean energy realised per lb. was 78'68 foot-tons, thus 
showing that no superior effect was thereby obtained. 
Two rounds were then fired with shell fitted with copper rings. The energy 
obtained was 82 foot-tons per lb. and the gain was real, but the chamber pressure ran 
up from a mean of 1G‘8 tons on the square inch to a mean of 18‘6 tons, thus showing 
that, at all events in great measure, the increased effect is caused not by the copper 
bands giving rise to less loss by friction, but to the fact that the increased difficulty of 
forcing the copper bands into the grooves permits the powder to become fully burned 
at an earlier point in the bore, and thus an increased effect from the powder is realised. 
But to show the effect of a greater or less degree of retention of the shot in its 
