[32] Principles of Psychology, part vii.
[33] Social Statics, chap. iii.
[34] Principles of Psychology, § 531.
[35] First Principles, § 34.
[36] Only after the foregoing paragraphs were written, did the remark of a distinguished friend show me how certain words were misconstrued by the reviewer in a way that had never occurred to me as possible. In the passage referred to, I have said that sound-waves “finally die away in generating thermal undulations that radiate into space;” meaning, of course, that the force embodied in the sound-waves is finally exhausted in generating thermal undulations. In common speech, the dying-away of a prolonged sound, as that of a church-bell, includes its gradual diminution as well as its final cessation. But rather than suppose I gave to the words this ordinary meaning, the reviewer supposes me to believe, not simply that the longitudinal waves of air can pass, without discontinuity, into the transverse waves of ether, but he also debits me with the belief that the one order of waves, having lengths measurable in feet, and rates expressed in hundreds per second, can, by mere enfeeblement, pass into the other order of waves, having lengths of some fifty thousand to the inch, and rates expressed in many billions per second! Why he preferred so to interpret my words, and that, too, in the face of contrary implications elsewhere (instance § 100), will, however, be manifest to every one who reads his criticisms.
[37] Other examples of these amenities of controversy, in which I decline to imitate my reviewer, have already been given. What occasions he supplies me for imitation, were I minded to take advantage of them, an instance will show. Pointing out an implication of certain reasonings of mine, he suggests that it is too absurd even for me to avow explicitly; saying:—“We scarcely think that even Mr. Spencer will venture to claim as a datum of consciousness the Second Law of Motion, with its attendant complexities of component velocities, &c.” Now any one who turns to Newton’s Principia, will find that to the enunciation of the Second Law of Motion, nothing whatever is appended but an amplified re-statement—there is not even an illustration, much less a proof. And from this law, this axiom, this immediate intuition or “datum of consciousness,” Newton proceeds forthwith to draw those corollaries respecting the composition of forces which underlie all dynamics. What, then, must be thought of Newton, who explicitly assumes that which the reviewer thinks it absurd to assume implicitly?
[38] That I am certainly not singular in this view, is shown to me, even while I write, by the just-issued work of Prof. Jevons on the Principles of Science: a Treatise on Logic and Scientific Method. In vol. ii., p. 141, Prof. Jevons remarks respecting the law of variation of the attractive force, that it “is doubtless connected at this point with the primary properties of space itself, and is so far conformable to our necessary ideas.”
[39] See Essay on “The Genesis of Science,” in the British Quarterly Review for July, 1854, p. 127.
[40] I do not say this at random. The reviewer, who has sought rather to make known than to conceal his identity, took his degree in 1868.
[41] It is true that in Newton’s time, “axiom” had not the same rigorously defined meaning as now; but it suffices for my argument that, standing unproved as a basis for physical deductions, it bears just the same relation to them that a mathematical axiom does to mathematical deductions.