CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 233 
values, together with those of the other constants used in equation (30), are given in 
Table IX. 
With regard to the value of X it is necessary to say a few words. If the tensions 
given in Table XVIII.* of our first memoir calculated from (30) be compared with the 
tensions actually observed in the bores of guns given in the same table, or if a com¬ 
parison be made between curves B and C in Plate 24 of the same memoir, it will 
be observed that for densities of the products of combustion of '4 and below, or, in 
other words, for 2f expansions and higher, the tensions actually observed with 
R, L. G. powder are in all cases higher than those calculated from equation (30). 
This, of course, should not be, as those last tensions should in actual practice only 
be reached if there were no loss from windage, vent, or other causes, if there were 
perfect combustion of the charge, and if the charge were expanded in a gun perfectly 
impervious to heat. 
We surmised t as one of the causes of this difference that in our calculations we had 
taken X at its mean value, whereas we pointed out that as the specific heat of the non- 
gaseous products must, according to our hypothesis, increase rapidly with the tempe¬ 
rature, X should for our purposes be taken at a considerably higher value. 
As however the agreement between the observed and calculated tensions was exceed- 
ingly close, as when the calculations were applied to guns, the “ factor of effect ” alone 
would practically be altered, and as, finally, we had not sufficient data to enable us to 
correct this constant with any certainty, we did not feel justified in attempting hypo¬ 
thetical corrections. 
But since the date of the submission of our first memoir to the Royal Society, our 
knowledge of the action of large charges in the bores of guns has been greatly increased; 
not only have charges seven or eight times as great £ as the largest of those then dis¬ 
cussed been fired, but we have submitted to careful calculation, with a full knowledge 
of all the necessary data, the results of a very large number of rounds fired from guns 
of all sizes, from the 100-ton gun down to the smallest gun in IT.B.M.’s service. In 
some of these guns also the charges were so arranged as to suffer a high degree of expan¬ 
sion, and we have thus accumulated data which have enabled us to deduce a corrected 
value of X, and which gives pressures and energies more closely in accordance with the 
whole of the experiments we have discussed. 
* Phil. Trans., 1875, Part I., p. 129. 
t Phil. Trans., loc. cit., p. 131. 
| The highest charge fired by the distinguished Italian artillerists who conducted the recent experi¬ 
ments with the 100-ton guns reached the great weight of 260 kilos. (573 lb.) of Fossano powder—a 
powder singularly well adapted for use in large guns. The velocity given to a projectile of 908 kilos. 
(2001'5 lb.) was (525‘9 metres) 1725'3 feet per second, and the energy of the shot at the muzzle reached 
the enormous amount of (12,800 metre tonnes) 41,333 foot-tons. The highest charge fired from the 80-ton 
gun has been (208'7 kilos.) 460 lb. prismatic powder. This charge gave to a projectile of 1705 lb. a 
muzzle velocity of (495'6 metres) 1626 feet per second and an energy of (9680 metre tonnes) 31,257 
foot-tons. 
MDCCCLXXX. 
2 H 
