LETTER FROM MAXWELL 115 



If not, you may write 



w = A + Br* + C*r* cos 2<f> + C t r* cos 4</> + etc., 

 where x = ar cos and y = br sin 6 and then 



and you satisfy (2) the best way you can when r= i. 



As to Ampere of course you may lay on d l (anything) where d^ is with 

 respect to the element of a circuit. Have you studied H" on the potential ' of two 

 elements? or Bertrand? who, with original bosh of his own rushes against the 

 thicker bosches of H*'s buckler and says that H 8 believes in a force which does not 

 diminish, with the distance, so that the reason why Ampere or H" or Bertrand 

 observe* peculiar effects is because some philosopher in a Centauri happens to be 

 completing a circuit. XQq D [tails]' as I am surrounded by Naturals and cannot 

 give references. 



In introducing 4nions s do so by blast of trumpet and tuck of drum. Why 

 should V. a/3y come in sneaking without having his style and titles proclaimed by 

 a fugleman ? Why even . should be treated with due respect and we should be 

 informed whether he is attractive or repulsive. 



What do you think of " Space-variation " as the name for Nabla ? 



It is only lately under the conduct of Professor Willard Gibbs that I have been 

 led to recant an error which I had imbibed from your 6k.cs, namely that the 

 entropy of Clausius is unavailable energy, while that of T' is available energy*. The 

 entropy of Clausius is neither one nor the other. It is only Rankine's Thermo- 

 dynamic Function.... 



I have also a great respect for the elder of those celebrated acrobats, Virial 

 and Ergal, the Bounding Brothers of Bonn. Virial came out in my paper on Frames, 

 R. S. E. 1870 in the form 2Rr = o, when there is no motion. When there is 

 motion the time average of $2,Rr = time average of ^Mv\ where R is positive 

 for attraction. 



But it is rare sport to see those learned Germans contending for the priority 

 of the discovery that the 2nd law of O&cs is the Hamiltonsche Princip, when 

 all the time they assume that the temperature of a body is but another name for the 

 vis viva of one of its molecules, a thing which was suggested by the labours of Gay 



1 The reference is to H(ermann) H(elmholtz)'s electrodynamic investigation which supplied 

 the true criterion in place of the hasty generalisation of 385 in the first edition of Thomson 

 and Tait. 



* The [tails] are drawn as arrow-headed wiggles of various lengths and forms. 



1 See the chapter on Quaternions for other remarks by Maxwell on Tail's quaternion 

 work. Maxwell was reading Kelland and Tail's Introduction to Quaternions which he reviewed 

 in Nature shortly after. 



4 Tait suggested in the first edition of his Thermodynamics (contracted into Obcs by Maxwell) 

 that the word Entropy should be used in this sense. In the second edition he went back to 

 the original meaning as given by Clausius. 



152 



