CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 
245 
It will be gathered from what has just been said that, with a little experience, if the 
factor of effect and maximum chamber pressure in any gun be known, the behaviour of 
the same powder in other guns, or in the same gun with other charges or weights of 
shot, can be anticipated. It was the consideration of the results embodied in Tables 
X. and XI. that allowed the high energies (more than twice as great as those obtained 
from the same calibres a few years back) to be predicted and realised ; to be realised, 
also, with less strain to the gun than when much smaller charges were fired, without 
attention being paid to the all-important point of the density of the products of explo¬ 
sion at the moment when such explosion may be considered to be completed. 
It will readily be understood from our remarks upon Table XI. that, to the artil¬ 
lerist, two descriptions of factors of effect are useful. One of these factors is employed 
to give the ratio between the work actually realised in a given gun, and the maximum 
work attainable by the charge (its gravimetric density being supposed to be unity). 
The value of this factor shows whether or not the charge is economically employed. 
The other factor is employed to denote the ratio between the work actually realised 
and the maximum work realisable by the charge, in expanding from the gravimetric 
density of the powder chamber to the mean density of the products of explosion, at the 
moment when the projectile leaves the muzzle of the gun. 
With respect to the first class of factors, it would obviously be difficult to lay down 
general rules. The value of the factor depends mainly upon the gravimetric density 
of the charge, but we may remark that, in the most modern guns, even with the 
advantage they possess of great absolute length, the powder is very uneconomically 
burned. With the very high charges and consequent small number of expansions, 
with the low gravimetric density also of the charge, the realised energy per pound of 
powder is necessarily much lower than was the case with the older guns. 
The same difficulty does not exist with regard to the second class of factors of effect. 
With respect to these, it may be enough to state that, in the smaller guns with 
R. L. G. powder, the factors of effect vary with a mild brand of powder from '71 to *76; 
with a specially violent brand, from ’82 to ‘89, the variations being chiefly dependent 
upon the principles we have already explained. 
In 6-incli guns, firing pebble powder of the normal quality, the factors of effect vary 
from 75 to '82; and, as the calibres of the guns are increased, the factors of effect 
likewise gradually increase, until, in the 80 and 100-ton guns, factors of from # 89 to '96 
have usually been reached. 
In concluding this memoir we desire to remark that, although the agreement be¬ 
tween the results of the long and laborious series of experiments and calculations 
which we now bring to a close have far exceeded the expectations we had formed when 
we commenced our task, it would yet be idle to suppose that many of our deductions, 
referring as they do to temperatures and tensions far above the range of ordinary 
research, will not require some subsequent correction. 
