176 Prof. Tait on some Questions in 



which Professor Boltzmann, without doubt justly, claims as 

 his own) is correct under the conditions by which I restricted 

 my investigation. The introduction of the consideration of 

 change of permeability due to the shearing motion involves 

 an alteration of about eleven or twelve per cent, only in this 

 avowedly approximate result. Of this I have assured myself 

 by a rough calculation, and I will work it out more rally 

 when I have leisure. It seems that I have missed this in 

 looking over Meyer's book, and, according to Prof. Boltzmann, 

 all investigators except Meyer have fallen into the same trap. 

 Meanwhile the calculation with which Prof. Boltzmann has 

 furnished me gives an excellent example of his style, for it is 

 altogether unnecessarily tedious. And it seems to contain two 

 gigantic errors which, however, compensate one another. 

 For his integrand contains the factor e~^p. Here / is a 

 signless quantity, and the limits show that x is always posi- 

 tive and p always negative. As written, therefore, the in- 

 tegral is infinite, though in the result it is made to come out 

 finite. The object of the paragraphs 1 and 2, which imme- 

 diately follow, is unintelligible to me. The former seems to 

 suggest the use of an unsound method ; the latter has no 

 discoverable bearing on anything that I have written. Prof. 

 Boltzmann has also afforded an idea of the value which he 

 himself attaches to the terrific array of symbols in the 95 

 pages of his 1881 paper (to which he refers me) by now 

 allowing that he is not prepared to assert that any one of 

 three determinations of the coefficient of viscosity which he 

 quotes (mine, or rather his own, being among them) is to be 

 preferred to the others ! 



Fourth. Prof. Boltzmann refers to my remarks on Mr. 

 Burbury's assertion that a single particle, with which they 

 can collide, would reduce to the special state a group of non- 

 colliding particles. Prof. Boltzmann signified his belief in 

 the truth of this proposition ; and in answer I showed that 

 (were it true) aeons would be required for the process, even 

 if that were limited to a single cubic inch of gas. He now 

 calls this an " entirely new question " and will not " prolong 

 the controversy by its discussion." I do not see that, so far 

 at least as the " controversy" is concerned, it is any newer 

 than the rest. It is contained in the first instalment of his 

 attack. Why, then, should he now desert it ? But Prof. 

 Boltzmann, in thus leaving the subject, takes a step well 

 calculated to prolong the discussion, for he represents me as 

 speaking of the instantaneous reversal of the motions of all 

 the particles, whereas my argument was specially based on 

 the reversal of the motion of the single stranger alone, a con- 



