CRITICISMS CORRECTED. 393 



our senses as deceiving us in the same way that the eyes do ; and so 

 makes us feel ourselves floating in a world of phantasms, Hadj^Ae- 

 nomenon and appearance no such misleading associations, little, if 

 any, of this mental confusion would result. Or did we in place of 

 them use the term effect, which is equally applicable to all impressions 

 produced on consciousness through any of the senses, and which carries 

 with it in thought the necessary correlative cause, with which it is 

 equally real, we should be in little danger of falling into the insanities 

 of idealism." This caution was intended for the general reader. That 

 it might be needed by one who should undertake to deal with the 

 work ci'itically never occurred to me. Not only, however, does it seem 

 that Professor Birks (who quotes the last three words of the para- 

 graph) needs such a caution, but it further seems that the caution is 

 thrown away upon him. For just those misinterpretations of the 

 words above pointed out, are the misinterpretations he makes. After 

 this I shall, I think, be absolved from examining further his metaphysi- 

 cal criticisms. 



Of his criticisms upon various of the physical doctrines which this 

 work contains, I will notice two only the one because I wish to repu- 

 diate a view which, spite of abundant evidence to the contrary, he 

 ascribes to me ; and the other, because, based as his statement is on a 

 fact which he misinterprets, it is desirable to give the right interpreta- 

 tion of it. On page 188, Professor Birks says : "The essence of the 

 doctrine held by Mr. Grove, Dr. Tyndall, and Mr. Spencer, and which 

 the last has made the foundation of his whole theory of physical fatal- 

 ism, is that there is, every moment, an unchanging total of force, 

 which never varies in amount, while it incessantly changes its form. 

 The force, then, which persists, must be a present existence. But 

 potential energy is nothing of the kind. It is the sum of trillions of 

 trillions of future possibilities of force, ranging through trillions of 

 trillions of different future intervals of time." Now, the tacit implica- 

 tion here is, that I accept the doctrine of potential energy. The men 

 of science named, with many others who might be added, hold that the 

 total quantity of force remains constant. Against these it is urged that 

 energy in becoming potential ceases to exist ; and that, therefore, the 

 doctrine is untrue. And being represented as holding this doctrine in 

 common with them, I am said to have based my general fabric of con- 

 clusions upon a fallacy. In the first place, I have to ask on what 

 authority Professor Birks assumes that I hold the doctrine of potential 

 energy in the way in which it is held by those named ? And in the 

 second place, I have to ask how it happens that Professor Birks, elabo- 

 rately criticising my views step by step, deliberately ignores the pas- 

 sages in which I have repudiated this doctrine ? In the chapter on " The 

 Continuity of Motion " I have, at considerable length, given reasons 

 for regarding the conception of potential energy as an illegitimate 

 one, and have distinctly stated that I am at issue with scientific 



