42 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
the truth of the dynamical theory of heat beyond all manner of 
doubt. His results have been extended by Helmholtz, Mayer, 
Clausius, and Thomson, till the law of conservation has been shown 
to govern all natural forces. 
Thomson demonstrated that Faraday’s discovery of the rotation of 
the plane of polarization of a polarized ray of light, produced by 
media under the influence of a powerful magnet, involved the 
dependence of magnetism on motion. 
The extension of the principles of the conservation and trans- 
formation of energy to physiological phenomena has been largely due 
to Helmholz and Carpenter. 
There can be no doubt that Maxwell’s electro-magnetic theory of 
light is destined to play no unimportant part in the development of 
the true theory of energy. From data supplied by Weber Maxwell, 
found that electro-magnetic disturbances were propagated with the 
same velocity as light. The explanation of this he held to be that 
electricity like light was due to the undulatory vibrations of the 
mediuin, which is beyond question necessary for the propagation of 
light. Should this hypothesis be found to bea valid one, a very 
clear insight will be obtained into the real connexion between 
electricity, light, and radiant heat. 
From what has preceded, it will be seen that the mysterious, 
all-pervading ether plays an increasingly important part in the 
prevailing physical theories. To such an extent is this the case that 
Tyndall has justly remarked that its relations to the matter of the 
universe must mainly occupy the investigations of future scientists. 
Tn order to form a more definite idea of the properties of this highly 
attenuated substance, which is yet so elastic and incompressible, that 
Stallo has characterised it as an adamantine solid, it is now proposed 
to attempt a calculation of its probable density. To accomplish this 
object, it is necessary to know the amount of radiant energy emitted 
by the sun. This determined by careful observations with the 
pyrheliometer, and expressed by means of Joule’s mechanical equiva- 
lent of heat, amounts to 5,500,000 foot-pounds per second from every 
square foot of the sun’s surface. 
Now, the velocity of light is 186,000 miles per second. " Therefore 
the radiant energy sent forth by the sun during any given second of 
time will at the end of that second be contained between two spheres, 
the smaller 433,000 miles, or the semi-diameter of the sun for radius, 
