problem, and it is undoubtedly fraught with the most important
consequences to both attack and defense. Difficult as it has been to
obtain an exact estimate of the force of different explosives under
water, the problem is far greater out of the water and under the
ordinary conditions of shell fire; the principal obstacle being in the
fact that it is physically impossible to control the force of large
quantities in order to measure it, and small quantities give irregular
results. Theoretically, the matter has been accomplished by Berthelot,
the head of the French government "Commission of Explosives," by
calculating the volume of gas produced, heat developed, etc.; and this
method is excellent for obtaining a fair idea of the specific pressure
of any new explosive that may be brought forward, and determining
whether it is worth while to investigate it further; but the
explosives differ so much from each other in point of sensitiveness,
weight, physical condition, velocity of explosive wave, influence of
temperature and humidity, that we cannot determine from mere
theoretical considerations all that we would like to know. Various
methods of arriving at comparative values have been tried, but the
figures are very variable, as will be seen by the following tables.
Berthelot's commission, some ten years ago, exploded ten to thirty
grammes of each in 300 pound blocks of lead and measured the increased
size of the hole thus made. The relative result was:

No. 1 dynamite 1.0
Dry gun-cotton 1.17
Nitro-glycerine 1.20

Powder blew out and could not be measured.

Mr. R.C. Williams, at the Boston Institute of Technology, in the