513 
of Edinburgh, Session 1868 - 69 . 
those atmospheric and ethereal vibrations which affect us with the 
sensations of sound and light. 
When I roll a ball along the ground I communicate force to it ; 
this force carries it forward till it encounters a body at rest, to which 
it communicates this force, and the force which came from me, may 
thus be transmitted or handed over, from ball to hall, through a 
lengthened series, subject only to such decrease as may arise from 
friction or other accidental obstructions. 
Mr Wyld called attention to the circumstance— first, that the balls 
successively received something which we call force ; second, that 
it is force which causes their movement, and not their movement 
which gives them their momentum or force. Their movement, 
however, seeing it is the result of the force, may be taken as a just 
measure of the force applied. 
Another instance of the transmission of force we have when we 
direct, what has for convenience been called the electric or galvanic 
fluid, through wire conductors. The transmission of this manifes- 
tation of force may be explained on nearly the same principle as 
the transfer of the momentum of moving bodies, and of the me- 
chanical vibratory force transmitted from molecule to molecule of 
the ethereal medium , which vibratory force we call light, and which 
reaches us after a passage of more than ninety-one millions of miles. 
Mr Wyld considered these to be instances of the action, and 
transmission of what may be called free, an-atomic, or transmissible 
power, which is not to be viewed as a substance or fluid, but either 
as an imponderable immaterial agent, or simply as the action of an 
unseen cause. 
Neither the nature of its origin, nor the nature of its transmission, 
nor the variety of its actions and operations, permit us to consider 
it as a substance. When we disintegrate crystals, when we separate 
the parts of fluids by evaporation, when we dissolve metals, or 
decompose compound bodies, organic or inorganic, we seem to 
obtain that force which held their parts together, in the form of 
free transmissible power. To this power we can by certain arrange- 
ments give a definite direction, and can transmit it through wire 
conductors. We can thus make it available for the production of 
many of the most important natural phenomena, for instance — ■ 
1. The production of intense artificial light. 
