4 20 SCIENCE PROGRESS 



motion, and derived from them a theory of matter which has 

 illumined the whole region of molecular physics. 



To write a full account of Lord Kelvin's work in science is 

 practically to write the history of modern science and to indicate 

 the bearing of modern lines of investigation. In almost every 

 branch of science his work is fundamental. His labours have 

 been extended by later workers and each field developed in 

 detail so that each worker realises the greatness of Lord 

 Kelvin's pioneering achievements only in his own domain. 

 In the presence of so extensive a volume of material no explana- 

 tion is required regarding the subjects dealt with in the following 

 pages other than that they constitute the present writer's main 

 line of interest in the work of Lord Kelvin and fall in best with 

 his experience. The intention is to sketch roughly his own 

 personal work with a view to arriving at the foundation of his 

 attitude to modern views on molecular physics, and to indicate 

 the bearing of his later work, with the developments which it 

 has received since his death in 1907, on modern speculations 

 regarding the mechanism of radiation. 



Some guiding principle is necessary to explain the appar- 

 ently miscellaneous and diverse nature of his earlier papers. 

 The ideas promulgated by Faraday, and his success in establish- 

 ing a relation between Magnetism and Light on the experimental 

 side, the scope of the work of Green, and the development by 

 Stokes of the analogy between equilibrium conditions of elastic 

 solids and viscous fluid motion, accompanied by Lord Kelvin's 

 own success in connecting Flow of Heat with Electrostatics and 

 Attraction, seem to have firmly rooted in his mind the conception 

 of the underlying unity of physical processes and, thus early in 

 his career, made the achievement of uniting the known laws of 

 Nature within a single scheme a dominating ambition of his 

 life. Evidence of this appears throughout his works. One of 

 the most prominent features of his writings is his fondness for 

 mathematical analogies. Almost from the beginning of his 

 writings we can trace the conscious extension of his range 

 along this line towards that " comprehensive dynamics of ether, 

 electricity, and ponderable matter, which shall include electro- 

 static force, magnetostatic force, electromagnetism, electro- 

 chemistry, and the wave theory of light " (Baltimore Lectures, 

 Preface). 



One of his earliest contributions to the Cambridge Math. 



