1908] on the Scientific Worh of Lord Kelvin. 225 



visions of pure reasoning : for there could be little opportunity for 

 making tentative experiments, according to the usual trial methods of 

 inventors, such as, for instance, have so rapidly and brilliantly 

 improved the arrangements for telegraphing across space, after Hertz 

 had taken the preliminary crucial step of discovering, or rather 

 recognising, the electric waves that are concerned in it. The neces- 

 sities of this cable problem led largely to the invention of the 

 fundamental principles of delicate and exact practical electrical 

 measurement ; and though their embodiment in apparatus has 

 naturally been subject to continuous improvement in detail, yet the 

 principles remain largely those evolved in the early days by Thomson 

 and his associates. 



Among the most potent causes of the general improvement in 

 physical modes of thought during the last third of the century, was 

 the appearance, in 1867, of what then purported to be merely the 

 first volume of the ' Treatise on Natural Philosophy,' by W. Thomson 

 and P. G. Tait, which has proved to be a turning point in the ex- 

 position and expression of physical science, at any rate in this country. 

 The preparation of this book, which had gone on for some years, 

 induced frequent visits by Thomson to his friend and disciple Tait, 

 at Edinburgh. Among other things, this treatise revised the ter- 

 minology of dynamics, which had been allowed to grow up, in many 

 respects, in forms that retained only historical meaning ; the impulse 

 thus given, which had indeed already been operating less system- 

 atically in the previous years, and was largely due doubtless to his 

 brother James Thomson, has led, in the hands of Maxwell, Heaviside 

 and others elsewhere, to greater attention to the language of science, 

 the introduction everywhere of expressive terms, which react power- 

 fully in inducing clearness of ideas. Another of the benefits conferred 

 by this work was that it served, in some degree, to focus the scattered 

 fragments of Thomson's own investigations and those of his asso- 

 ciates, and to exhibit his scientific method, as exemplified in the 

 subjects covered in this first instalment, which contained general 

 kinematics and dynamics, general theory of the potential, and theory 

 of elasticity with extensive geodetic application. 



A translation of this book into German, by Helmholtz and 

 Wertheim, appeared in 1871-4. In a preface, Helmholtz pointed 

 out how it satisfied, in very remarkable manner, a most urgent want 

 in higher scientific literature. Previously there had been no resource 

 but to go to original memoirs, difficult of access even if one knew 

 where to find them ; and on this account the recent progress of con- 

 nected mathematical physical thought had been halting. Moreover, 

 as he said, when a worker like Sir William Thomson admits us to 

 participate in the very upbuilding of his ideas, exhibits to us the 

 modes of intuition, the guiding threads, which have helped him, by 

 bold combinations of thought, to control and arrange his refractory 



YoL. XIX. (No. 102) Q 



