lx REPORT—1863. 
essentially distinct from force. Dr. Young has shown that even in so dense 
a body as water, these nuclei, if they exist at all, must be so small in relation 
to the intervening spaces, that a hundred men distributed at equal distances 
over the whole surface of England would represent their relative magnitude 
and distance. What then must be these relative dimensions in highly rarefied 
matter? But why encumber our conceptions of material forces by this unneces- 
sary imagining of a central molecule? If we retain the forces and reject the 
molecule, we shall still have every property we can recognize in matter by 
the use of our senses or by the aid of ourreason. Viewed in this light, matter 
is not merely a thing subject to force, but is itself composed and constituted 
of force. 
The dynamical theory of heat is probably the most important discovery of the 
present century. We now know that each Fahrenheit degree of temperature 
in a pound of water is equivalent to a weight of 772 Ibs. lifted 1 foot high, 
and that these amounts of heat and power are reciprocally convertible into 
one another. This theory of heat, with its numerical computation, is chiefly 
due to the labours of Mayer and Joule, though many other names, including 
those of: Thomson and Rankine, are deservedly associated with its develop- 
ment, I speak of this discovery as one of the present age because it has 
been established in our time; but if we search back for earlier concep- 
tions of the identity of heat and motion, we shall find (as we always do in 
such cases) that similar ideas have been held before, though in a clouded and 
undemonstrated form. In the writings of Lord Bacon we find it stated 
that heat is to be regarded as motion and nothing else. In dilating upon 
this subject, that extraordinary man shows that he had grasped the true 
theory of heat to the utmost extent that was compatible with the state of 
knowledge existing in his time. Even Aristotle seems to have entertained 
the idea that motion was to be considered as the foundation not only of heat, 
but of all manifestations of matter; and, for aught we know, still earlier 
thinkers may have held similar views. 
The science of gunnery, to which I shall make but slight allusion on this 
occasion, is intimately connected with the dynamical theory of heat. When 
gunpowder is exploded in a cannon, the immediate effect of the affinities by 
which the materials of the powder are caused to enter into new combinations, 
is to liberate a force which first appears as heat, and then takes the form of 
mechanical power communicated in part to the shot and in part to the pro- 
ducts of explosion which are also propelled from the gun. The mechanical 
force of the shot is reconverted into heat when the motion is arrested by 
striking an object, and this heat is divided between the shot and the object 
struck, in the proportion of the work done or damage inflicted upon each, 
These considerations recently led me, in conjunction with my friend Captain 
Noble, to determine experimentally, by the heat elicited in the shot, the loss 
of effect due to its crushing when fired against iron plates. Joule’s law, and 
the known velocity of the shot, enabled us to compute the number of dyna- 
mical units of heat representing the whole mechanical power in the projectile, 
and by ascertaining the number of units developed in it by impact, we arrived 
at the power which took effect upon the shot instead of the plate. These ex- 
periments showed an enormous absorption of power to be caused by the 
yielding nature of the materials of which projectiles are usually formed ; but 
further experiments are required to complete the inquiry. 
Whilst speaking of the subject of gunnery, I must pay a passing tribute of 
praise to that beautiful instrument invented and perfected by Major Navez of 
the Belgian Artillery, for determining, by means of electro-magnetism, the 
