[27] We are aware that a certain class of thinkers regard all matter and combinations of matter as in some unexplained sense alive. We will discuss this doctrine in another place; meanwhile it must be understood that we do not here allude to this peculiar life, which from its very conception must exist as truly in a dead body as in a living one; what we are discussing at present is individual consciousness of the ordinary recognised type. [28] As will be seen in Chap. III., the more important half of the realities of the physical world are forms of Energy, _which cannot exist_ except when associated with Matter. We mention this merely in a footnote now, as we do not wish to diverge too far from our present line of argument. [29] A very striking analogy to this will be found in Chapter III., where it is shown that energy of visible motion often disappears by transformation into the dormant or latent energy of position. [30] See Essay on this subject by the Hon. Sir W. R. Grove, in his book on _The Correlation of Physical Forces_. [31] See _Contributions to Solar Physics_, by De la Rue, Stewart, and Loewy. [32] In Chap. IV. the reader will see that the only attempt to explain the mechanism of gravitation, which can be called even _hopeful_, does not give _rigorously_ the law of the inverse square of the distance. [33] ‘I hope all will be well. And, as for the gate you talk of, all the world knows that it is a great way off our country. I cannot think that any man in all our parts doth so much as know the way to it; nor need they matter whether they do or no, since we have, as you see, a fine, pleasant, green lane, that comes down from our country, the next way into the way.’ [34] This is discussed in Chapter IV. below. [35] It is hardly needful to inform our readers that the word _substance_ is used in this chapter in the ordinary sense. [36] See Thomson and Tait’s _Natural Philosophy_, § 269; or Tait’s _Thermodynamics_, § 91. [37] Thus paraphrased for us:— Nature, bewildering in diversity, Of marvels Marvel most inscrutable, Like Proteus, altereth her shape and mould; But Fate remaineth ever immovable, And, changeless in persistency, outwears The Time of men, the gods’ Eternity. [38] For a more complete statement of Carnot’s work see Tait, _Recent Advances in Physical Science_, 1876. [39] They virtually showed that in a perfect steam-engine with pressure equal to ‘one atmosphere’ in its boiler, and with its condenser at the temperature of melting ice, the ratio of the heat taken in to the heat given out is 1·365 to 1. Hence if the difference between the numbers is to be 100, these must be 374, 274.—_Phil. Trans._, 1854. [40] See Tait, _Phil. Mag._, 1872, I. 338, 516; II. 240. [41] Thomson and Tait’s _Natural Philosophy_, § 300; or Tait and Steele’s _Dynamics of a Particle_, 3d ed. § 299.