: : ADDRESS. lix 
* of Young; but it continued to hold its ground, and is interwoven into the 
language of science. It is now clearly shown to be self-contradictory ; and 
to lead to the result, that the amount of heat in the universe may be indefi- 
nitely augmented, On the other hand, the identification of radiant heat with 
light, and the establishment of the wave-theory, left little doubt that heat 
eonsisted in a vibratory movement either of the molecules of bodies, or of 
the ether within them, Still, the relation of heat to bodies, and the phenomena 
of conduction, indicate a mechanism of a more complicated kind than that of 
_ light, and leave ample room for further speculation. 
The only mechanical hypothesis (so far as I am aware) which is consistent 
with the present state of our knowledge of the phenomena of heat, is the 
theory of molecular vortices of Mr, Rankine. In this theory all bodies are 
supposed to consist of atoms, composed of nuclei surrounded with elastic 
atmospheres. The radiation of light and heat is ascribed to the transmission 
of oscillations of the nuclei; while thermometric heat is supposed to consist 
in circulating currents, or vortices, amongst the particles of their atmospheres, 
whereby they tend to recede from the nuclei, and to occupy a greater space. 
From this hypothesis Mr. Rankine has deduced all the laws of thermo- 
_ dynamics, by the application of known mechanical principles. He has also, 
from the same principles, deduced relations (which have been confirmed by 
experiment) between the pressure, density, and absolute temperature of 
elastic fluids, and between the pressure and temperature of ebullition of 
liquids. 
The dynamical theory of heat enables us to frame some conjectures to 
account for the continuance of its supply, and even to speculate as to its 
source. The heat of the Sun is dissipated and lost by radiation, and must 
i be progressively diminished unless its thermal energy be supplied. According 
_ to the measurements of M. Pouillet, the quantity of heat given out by the 
_ Sun ina year is equal to that which would be produced by the combustion of 
a stratum of coal seventeen miles in thickness; and if the Sun’s capacity for 
heat be assumed equal to that of water, and the heat be supposed to be 
drawn uniformly from its entire mass, its temperature would thereby undergo 
a diminution of 2°4 Fahr. annually. 
_ On the other hand, there is a vast store of force in our System capable of 
‘conyersion into heat. If, as is indicated by the small density of the Sun, 
and by other circumstances, that body has not yet reached the condition of 
incompressibility, we have, in the future approximation of its parts, a fund 
} of heat probably quite large enough to supply the wants of the human 
family to the end of its sojourn here. It has been calculated that an amount 
of condensation, which would diminish the diameter of the Sun by only the 
ten-thousandth part, would suffice to restore the heat emitted in 2000 years. 
_ Again, on our own Earth, vis viva is destroyed by friction in the ebb and 
flow of every tide, and must therefore reappear as heat. The amount of this 
_ must be considerable, and should not be overlooked in any estimation of the 
