TAIT'S FIRST REPLY TO SPENCER 281 



This argument cleverly evades the real question by attacking a some- 

 what infelicitous way of stating the important principle that, apart from 

 experiment and observation, the human mind cannot formulate the laws of 

 nature. In its assumption of the meaning of the word axiom, it disregards 

 the obvious meaning of Thomson and Tail's statements in the very paragraph 

 quoted ("T and TV 243). Spencer seemed to have recognised this, for 

 he no longer contended that Thomson and Tait gave any support to his 

 view; but he still continued to assert that Newton must himself have regarded 

 the Laws of Motion as a priori principles (Replies to Criticisms, p. 326). 

 In response to Spencer's challenge Tait now entered the field and penned 

 the following short letter to Nature, March 26, 1874. 



HERBERT SPENCER -versus THOMSON AND TAIT. 



A friend has lent me a copy of a pamphlet recently published by Mr Herbert 

 Spencer, in which certain statements of mine are most unsparingly dealt with, 

 especially in the way of attempted contrast with others made by Sir W. Thomson 

 and myself. I am too busy at the present season to do more than request you to 

 reprint one of the passages objected to (leaving it to your readers to divine to what 

 possible objections it is open), and to illustrate by a brief record of my college days 

 something closely akin to the mental attitude of the objector. 



" Natural Philosophy is an experimental, and not an intuitive science. No a 

 priori reasoning can conduct us demonstratively to a single physical truth " (Tait, 

 Thermodynamics, p. i). 



One of my most intimate friends in Cambridge, who had been an ardent 

 disciple of the late Sir W. Hamilton, Bart, and had adopted the preposterous notions 

 about mathematics inculcated by that master, was consequently in great danger of 

 being plucked. His college tutor took much interest in him, and for a long time 

 gave him private instruction in elementary algebra in addition to the college lectures. 

 After hard labour on the part of each, some success seemed to have been obtained, 

 as my friend had at last for once been enabled to follow the steps of the solution 

 of a question involving a simple equation. A flush of joy mantled his cheek, he 

 felt his degree assured, and he warmly thanked his devoted instructor. Alas, this 

 happy phase had but a brief duration ; my friend's early mental bias too soon 

 recovered its sway, and he cried in an agony of doubt and despair, " But what if x 

 should turn out, after all, not to be the unknown quantity?" 



Compare this with the following extract from Mr Spencer's pamphlet: 



"... if I examine the nature of this proposition that 'the properties of matter 

 might have been ' other than they are. Does it express an experimentally-ascertained 

 truth? If so, I invite Prof. Tait to describe the experiments!" 



P. G. TAIT. 



In his reply published in Nature, April 2, Spencer complained that 

 T. 36 



