[161] Thomson and Tait, "Natural Philosophy," vol. i. p. 194; also Helmholtz, in "Correlation and Conservation of Forces," p. 242.
[162] Winchell, "Sketches of Creation," p. 422. If the whole solar radiation were employed in dissolving a layer of ice inclosing the sun, it would dissolve a stratum ten miles and a half thick in one day.
[163] Helmholtz, "Correlation and Conservation of Forces," p. 245.
[164] Energy is now defined as "the power of doing work," that is, the power, in virtue of its position (as a head of water, a raised mass, a coiled spring) or in virtue of its motion (as a falling mass, a current of wind, a projectile), to do work. The first is called Potential, the second Kinetic Energy. Besides these instances of Visible Energy, there is also Invisible Molecular Energy, divided into, (a) the Energy of electricity in motion; (b) the Energy of radiant heat and light; (c) the kinetic Energy of absorbed heat; (d) molecular potential Energy; (e) potential Energy caused by electrical separation; (f) potential Energy caused by chemical separation. Of these different kinds of Energy, the most available for work is Mechanical Energy, or Energy of visible motions and positions; the least available is universal heat, or radiant Energy.
[165] See article "Energy," in North British Review, May, 1864, and Balfour Stewart's "Treatise on Heat," p. 370.
[166] Stewart's "Elements of Physics," p. 357.
[167] "Die Naturkräfte in ihrer Wechselbeziehung," p. 89.
[168] "Correlation of Physical Forces," p. 187.
[169] American Journal of Science, July, 1864.
[170] Argyll, "Reign of Law," p. 121.