506 Proceedings of Societies . [July, 
removed from the truth for the principal powders with which 
they then experimented. The authors then discuss the constants 
in the equation, expressing the relation between the tension of 
the products of explosion and the volume these products occupy, 
as stated by them in their first memoir, and give values of those 
constants, corredted from the analyses and experiments made 
since the publication of that memoir, concluding their remarks 
upon this part of their subject with a table which gives in terms 
of the mean density of the powder products the tensions which 
would exist in the bores of guns were perfectly dry powder of 
normal composition suffered to expand, with or without produc- 
tion of work. The tensions are expressed in kilogrammes per 
square centimetre, tons per square inch, and atmospheres. The 
authors call attention to the great utility of a table (XI.) showing 
the theoretic work which a charge of gunpowder is capable of 
effecting in expanding to any value, v . The table given by them 
exhibits the theoretic work for all necessary volumes of v, from 
v=i to 21=50. The authors then discuss the causes which in 
the bore of a gun affedt the energy realised by gunpowder, and 
point out that this energy varies very much with the powders 
employed, being in this respedt dependent upon circumstances, 
such as the density of the powder, its size of grain, the amount 
of moisture, chemical composition, nature of charcoal used, &c., 
but that the energy 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 fadtor of effedt, 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 effedt, unless modified by other cir- 
cumstances, is produced when the charge is increased with the 
same weight of projedtile. In this case the projedtile has to 
traverse a greater length of bore before the same relief due to 
expansion is attained. The higher pressures which consequently 
rule read! upon the rate of combustion of the powder, and again 
a somewhat higher energy is obtained. Both these increased 
effedls, 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. The authors draw attention to the effedt of retaining 
the shot in its seat for a greater or less time, thus giving rise in 
the former case to a more perfedt and earlier combustion of the 
charge. They cite experiments to show that from this cause 
alone differences of energy in guns having a calibre of 12 centims. 
of 13 to 14 per cent have been obtained. It is pointed out that 
from the principles laid down it is possible, if the maximum 
chamber-pressure be known, to fix, very approximately, the posi- 
tion of the shot in the bore when the combustion of the charge 
