276 PETER GUTHRIE TAIT 



1. The work is far too much a mere display of mathematical skill. It soars above 

 such trifles as historical details, while overlooking in great measure the experimental 

 bases of the theory ; and it leaves absolutely unnoticed some of the most important 

 branches of the subject. 



(Thus, for instance, Sadi Carnot gets far less than his due, Rankine is not alluded 

 to, and neither Thermodynamic Motivity nor the Dissipation of Energy is even 

 mentioned !) 



2. It gives an altogether imperfect notion of the true foundation for the reckoning 

 of absolute temperature. 



3. It completely ignores the real (i.e. the statistical) basis of the Second Law of 

 Thermodynamics. 



On March 24, Poincar gave his reasons why, in the cases cited, he did 

 not discuss the questions in the way desired by Tail. A final letter from 

 Tait on April 7 ended the discussion. As was customary in such discussions, 

 Tait sent a proof of this letter to Kelvin. The proof has been preserved, 

 and is interesting inasmuch as it shows that Kelvin was in entire agreement 

 with Tait. In his first letter Poincair had referred to the distinction between 

 true and apparent electromotive forces ; and Tait replied : 



It is necessary to add that I made no reference whatever to M. Poincar's 

 distinctions between " true " and " apparent " electromotive force ; simply because 

 I regard these, along with many other celebrated terms such as " disgregation " etc., 

 as mere empty names employed to conceal our present ignorance. 



Kelvin underlined the words " regard these " and wrote in the margin 

 "So do I, K." Other annotations were even more definite in their expression, 

 and Kelvin's general acquiescence in the position taken by Tait was indicated 

 by the brief note appended to the sheet, "Netherhall, Mar. 28/92 OT OK K." 



Tait's review of A. McAulay's Utility of Quaternions in Physics 

 appeared in Nature, Dec. 28, 1893 (Vol. XLIX) under the title "Quaternions 

 as an Instrument in Physical Research." The following are some of the 

 characteristic passages : 



Just as "one shove of the bayonet" was truly said to be more effective than any 

 number of learned discussions on the art of war: this really practical work, giving 

 genuine quaternion solutions of new problems as well as largely extended developments 

 of old ones, is of incomparably greater interest and usefulness than the recently 

 renewed, but necessarily futile, attempts to prove that a unit vector cannot possibly be 

 a quadrantal versor.... 



Here, at last, we exclaim, is a man who has caught the full spirit of the quaternion 

 system : " the real aestus, the awen of the Welsh bards, the divinus afflatus that 

 transports the poet beyond the limits of sublunary things !"... Intuitively recognising 



