i6 4 POPULAR SCIENCE MONTHLY. 



ophy. Through the works and the personal influence of Hamilton he 

 was led to the study of quaternions, to which he gave much attention. 



In 1860 he was elected to the chair of natural philosophy in Edin- 

 burgh, resigning it in February, 1901, on account of a lingering illness, 

 which resulted in his death four months later. It is estimated that 

 about ten thousand students passed through his class-room during 

 those forty years, and few could do so without carrying away some 

 impress from this notable teacher. Among the first of his 'researchers' 

 were a remarkable trio — Eobert Louis Stevenson, Wm. Eobertson 

 Smith, the distinguished Scottish Biblical scholar and orientalist, and 

 Sir John Murray, the well-known publisher. Great must have been the 

 attraction of Tait's personality to bring together three men so highly 

 distinguished, yet so utterly different. 



About the time of his appointment to the Edinburgh chair, Tait 

 became acquainted personally with Lord Kelvin, who, though also 

 a Peterhouse man, had left Cambridge before Tait came up, "and was 

 already independently and in conjunction with Joule, and concurrently 

 with Eankine and Clausius, writing his classical memoirs on the theory 

 of energy. The first edition of Tait and Steele's 'Dynamics of a 

 Particle/ published in 1856, does not contain either of the words work 

 or energy. In its original form it was founded on Pratt's 'Mechanical 

 Philosophy/ and written on the old-fashioned Cambridge lines, which 

 knew not of Lagrange and Hamilton. Six years later it is on record 

 that in his introductory lecture Tait handled the notions of the 

 energetic school with freedom and laid down the foundations of a 

 thoroughly modern course in physics. Probably, therefore, he had come 

 under the influence of Joule and Kelvin before he met the latter per- 

 sonally." The conjunction with Kelvin produced the famous treatise 

 on 'Natural Philosophy' by Thomson and Tait in 1867, which began 

 a new era in mathematical physics. Dozens of men nourished by the 

 strong meat of its pages have written treatises in continuation of the 

 lines there laid down. 



Tait's contributions to text-book literature include, besides the two 

 works just mentioned, 'Elements of Quaternions/ 1867; 'Introduction 

 to Quaternions' by Kelland and Tait, 1868; 'Recent Advances in 

 Physical Science/ 1876; 'Thermodynamics/ 1868; 'Light/ 'Heat/ 

 1884; 'Properties of Matter/ 1885 (revised to 1899), and 'Dynamics/ 

 1895. 



Although Tait rarely spoke on religious topics, and in general 

 avoided theological controversy, his friends were aware that he held 

 decided views on such matters. He was the joint author with Balfour 

 Stewart of the 'Unseen Universe' (first printed privately in 1875), a 

 book showing, to use Tait's own words, how baseless is the common 

 belief that science is incompatible with religion. "It calls attention 



