of the molecules of matter, shown by the uniform pressure of the air in this room;
(10) of the combination and dissociations of molecules, as shown respectively by any combustion and any electrolytic decompositions.
2. Phenomena not hitherto explained.
That the physical properties demanded for the mechanical explanation of the ten phenomena illustrated, as well as others, exist, is certain.
But it is equally certain, that, hitherto, they had not been found, in spite of all attempts.
3. Theories of the transmission of light.
In place of explanations there have been the theories of Huygens and Newton, two hundred years ago, put forward as explaining, in some measure, the transmission of light; and again, the modification of Huygens' theory, by Dr Young, a hundred years ago, which latter up to the present time has carried all before it.
Thus for the last hundred years the idea of the structure of the universe, or the luminiferous ether, which has prevailed, is that of space occupied by an incompressible elastic jelly yielding to tangential stress, having a density which is all but indefinitely small.
And so the idea which has alone prevailed
