[261] "Familiar Lectures on Scientific Subjects," pp. 469-472.
[262] "Natural Philosophy," vol. i. pp. 190, 191.
[263] Ibid. p. 194.
[264] North British Review, vol. xl. pp. 182, 183.
[265] Helmholtz, "Correlation and Conservation of Forces," p. 245.
[266] This is the hypothesis of Helmholtz, Mayer, and Thomson.
[267] Tyndall, "Fragments of Science," p. 31; Murphy, "Habit and Intelligence," vol. i. p. 23.
[268] Murphy, "Habit and Intelligence," vol. i. p. 43.
[269] Professor Norton, "On Molecular Physics;" American Journal of Science and Arts, vol. iii, 3d Series, pp. 329-331.
[270] Tyndall, "Fragments of Science," p. 76.