286 PETER GUTHRIE TAIT 



become a critic because he quotes, with commendation if you like, a clever piece 

 of analysis or exposition published by another? 



Mr Spencer complains that an American critic (whose estimate is "tacitly" 

 agreed in by Mr Matthew Arnold) says of the "Formula of Evolution": "This 

 may be all true, but it seems at best rather the blank form for a universe than anything 

 corresponding to the actual world about us." On which I remark, with Mr Kirkman, 

 " Most just, and most merciful ! " But mark what Mr Spencer says : 



" On which the comment may be that one who had studied celestial mechanics 

 as much as the reviewer has studied the general course of transformations, might 

 similarly have remarked that the formula 'bodies attract one another directly as 

 their masses and inversely as the squares of their distances,' was at best but a 

 blank form for solar systems and sidereal clusters." 



We now see why Mr Spencer calls his form of words a Formula, and why he 

 is indignant at its being called a Definition. He puts his Formula of Evolution 

 alongside of the Law of Gravitation ! Yet I think you will very easily see that it 

 is a definition, and nothing more. By the help of the Law of Gravitation (not very 

 accurately quoted by Mr Spencer) astronomers are enabled to predict the positions 

 of known celestial bodies four years beforehand, in the Nautical Almanac, with an 

 amount of exactness practically depending merely upon the accuracy of the observations 

 which are constantly being made : and, with the same limitation, the prediction 

 could be made for 1900 A.D., or 2000 A.D., if necessary. If now Mr Spencer's form 

 of words be a formula, in the sense in which he uses the term as applied to the Law 

 of Gravitation, it ought to enable us to predict, say four years beforehand, the history 

 of Europe, with at least its main political and social changes ! For Mr Spencer says 

 that his "formula" expresses "all orders of changes in their general course, astronomic, 

 geologic, biologic, psychologic, sociologic"; and therefore "could not possibly be framed 

 in any other than words of the highest abstractness." 



Of Mr Spencer's further remarks there are but three which are directed specially 

 against myself. (Mr Kirkman is quite able to fight his own battles.) He finds evidence 

 of "idiosyncrasies" and what not, in the fact that, after proclaiming that nothing 

 could be known about the physical world except by observation and experiment, 

 I yet took part in writing the " Unseen Universe " ; in which arguments as to the 

 Unseen are based upon supposed analogies with the seen. He says: "clearly, the 

 relation between the seen and the unseen universes cannot be the subject of any 

 observation or experiment ; since, by the definition of it, one term of the relation 

 is absent." I do not know exactly what " mental peculiarity " Mr Spencer exhibits 

 in this statement. But it is a curious one. Am not I, the thinker, a part of the 

 Unseen ; no object of sense to myself or to others ; and is not that term of relationship 

 between the seen and the Unseen always present ? But besides this, Mr Spencer 

 mistakes the object of the book in question. The theory there developed was not 

 put forward as probable, its purpose was attained when it was shown to be conceivable 

 and not inconsistent with any part of our present knowledge. 



Mr Spencer's second fault-finding is a propos of a Review of Thomson and Tarts 

 Nat. Phil. (Nature, July 3, 1879) by Clerk Maxwell. Maxwell, knowing of course 

 perfectly well that the authors were literally quoting Newton, and that they had 



