[251] Spencer, "First Principles," p. 128.

[252] Montesquieu, "Spirit of Laws," bk. i. ch. i.

[253] Herschel, "Natural Philosophy," § 27.

[254] "Astronomy and Physics," p. 224.

[255] Thomson and Tait, "Natural Philosophy," vol. i. p. 164; Mayer, "Correlation and Conservation of Forces," p. 335.

[256] Stewart's "Physics," p. 103.

[257] Stewart's "Physics," pp. 114, 353.

[258] Stewart's "Physics," p. 356.

[259] Murphy, "Habit and Intelligence," vol. i. p. 22.

[260] Professor Charles Brooke, in Nature, vol. vi. p. 125.