[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. [42] The above letter, written after absence at Easter had involved a week’s delay, and written somewhat hurriedly to prevent the delay of a second week, was less carefully revised than it should have been. The words in square brackets, obviously implied by the reasoning, and specifically implied by the illustrations, were not in the letter as originally published. [43] Here, in explaining the genesis of special space-intuitions, I have singled out a group of experiences which, in _Nature_, May 28, Mr. Hayward had chosen as illustrating the absurdity of supposing that the scientific conception of proportionality could be reached as alleged. He said:― “It is hardly a parody of Mr. Collier’s remarks to say:—‘A child discovers that the greater the angle between his legs the greater the distance between his feet, an experience which implicates the notion of proportionality between the angle of a triangle and its opposite side;’ a preconception, as it appears to me, with just as good a basis as that whose formation Mr. Collier illustrates, but one which, as I need hardly add, is soon corrected by a conscious study of geometry or by actual measurement.”