PETER GUTHRIE TAIT. 165 



to the simple fact, ignored by too many professed instructors of the 

 public, that human science has its limits, and that there are realities 

 with which it is altogether incompetent to deal." 



Tait's collected scientific memoirs have been published by the Pitt 

 Press, and embrace between one hundred and two hundred papers 

 relating to a great variety of subjects. It would be out of place in this 

 paper to attempt any detailed examination of these articles. A rapid 

 sketch of the contents of the two volumes already published will 

 however be given. 



A large proportion of each volume is given up to quaternion investi- 

 gations, a subject and method in which Tait remains almost the sole 

 authority. Lord Kelvin has given the following reminiscence of the 

 collaboration in 'Natural Philosophy': "We had a thirty-eight years' 

 war over quaternions. He (Tait) had been captivated by the originality 

 and extraordinary beauty of Hamilton's genius in this respect, and had 

 accepted, I believe, definitely from Hamilton to take charge of quater- 

 nions after his death, which he has most loyally executed. Times without 

 number I offered to let quaternions into Thomson and Tait, if he could 

 only show that in any case our work would be helped by their use. You 

 will see that from beginning to end they were never introduced." In 

 a note in his second volume Tait states that Klein's account of 

 quaternions rests on a misapprehension; and remembering that, 

 though 'the grandest characteristic of quaternions is their trans- 

 parent intelligibility,' men like Cayley and Klein have gone astray, we 

 may be excused from any attempted discussion of them here. Other 

 abstruse papers are those on 'Amphicherial Knots,' and 'Knottedness.' 

 Many addresses and notes of a less technical nature serve, as Lord 

 Eayleigh has remarked concerning his own, 'to relieve the general 

 severity.' Here and there a biographical notice as of Listing, Kirchhoff, 

 Sir Wm. E. Hamilton and Eankine, or the reprint of an encyclopedian 

 article, as on 'Mirage,' 'Force,' etc., gives interest to the miscellany. 

 Tait was a party — and an active party — to many polemical discussions, 

 but very properly all traces of these keen controversies are omitted in 

 his collected papers. 



We have yet to notice the best of his researches. The most note- 

 worthy theoretical discussions are those on the kinetic theory of gases 

 (five papers, Trans. Edin. Roy. Soc, 1886-92), on impact (three papers, 

 1888-92), and on the path of a rotating spherical projectile. These 

 latter were due to his interest in golf, and on this subject he wrote a 

 series of popular articles, which it is said were widely read and appre- 

 ciated. 



His most important theoretical paper is the review of the kinetic 

 theory of gases, in which he analyzed into their logically simplest 

 elements, the first principles of a difficult subject. He gave several new 



