254 NOTICES OF THE MEETINGS (Feb. 11, 
WEEKLY EVENING MEETING, 
Friday, February 11. 
Tue Duke or NorTHUMBERLAND, K.G., F.R.S., President, 
in the Chair. 
Joun Tynpatt, Esa., Ph. D., F.R.S. 
On the influence of Material Aggregation upon the manifestations 
of Force. 
THERE are no two words with which we are more familiar than 
matter and force. The system of the universe embraces two things,— 
an object acted upon, and an agent by which it is acted upon ;— the 
object we call matter, and the agent we call force. Matter, in cer- 
tain aspects, may be regarded as the vehicle of force; thus the 
luminiferous ether is the vehicle or medium by which the pulsations 
of the sun are transmitted to our organs of vision. Or to take a 
plainer case; if we set a number of billiard ballsin a row and impart 
a shock to one end of the series, in the direction of its length, we 
know what takes place ; the last ball will fly away, the intervening 
balls having served for the transmission of the shock from one end 
of the series to the other. Or we might refer to the conduction of 
heat. If, for example, it be required to transmit heat from the fire 
to a point at some distance from the fire, this may be effected by 
means of a conducting body — by the poker for instance: thrusting 
one end of the poker into the fire it becomes heated, the heat makes 
its way through the mass, and finally manifests itself at the other 
end. Let us endeavour to get a distinct idea of what we here call 
heat; let us first picture it to ourselves as an agent apart from the 
mass of the conductor, making its way among the particles of the 
latter, jumping from atom to atom, and thus converting them into a 
kind of stepping-stones to assist its progress. It is a probable con- 
clusion, even had we not a single experiment to support it, that the 
mode of transmission must, in some measure, depend upon the man- 
ner in which those little molecular stepping-stones are arranged. 
But we need not confine ourselves to the material theory of heat. 
Assuming the hypothesis which is now gaining ground, that heat, 
instead of being an agent apart from ordinary matter, consists in a 
motion of the material particles; the conclusion is equally probable 
that the transmission of the motion must be influenced by the man- 
ner in which the particles are arranged. Does experimental science 
furnish us with any corroboration of this inference? It does. More 
than twenty years ago MM. De la Rive and De Candolle proved that 
heat is transmitted through wood with a velocity almost twice as 
great along the fibre as across it. This result has been recently 
expanded, and it has been proved that this substance possesses three 
