KINETIC OR MECHANICAL VIEW OF NATURE. 57 



and Bunsen's spectrum analysis, so in the closely related 

 doctrine of heat, probably no publication did more to 

 establish a general kinetic view of matter and of natural 

 phenomena than Tyndall's celebrated treatise, ' Heat as a 

 Mode of Motion.' In spite of the criticisms which 

 have been levelled against this expression, 1 the book, 

 which appeared in 1863, was to the popular mind a 

 revelation ; it was translated into many foreign languages, 

 ran through many editions, was recommended by thinkers 

 of the first order, and the title coveted as " manifesting 

 far and wide through the world one of the greatest 

 discoveries of modern philosophy." ' 2 It is the popular 

 herald of the kinetic or mechanical view of nature. 



The same great authority who has so generously 

 referred to Tyndall's treatise Lord Kelvin had been 

 inspired from quite a different quarter to suggest the 

 most advanced conception, in this line of thought, of 

 which the human mind has so far been capable : the 



38. 



Tyndall's 

 ' Heat.' 



39. 

 Lord 

 Kelvin's 

 vortex 

 theory of 

 matter. 



1 Notably by Prof. P. G. Tait ; 

 see his volume on ' Heat,' p. 350, 

 also his ' Recent Advances of 

 Physical Science,' which contains 

 as an appendix his lecture on 

 " Force," delivered in Glasgow on 

 the occasion of the meeting of 

 the British Association. He says 

 there : " Heat and kinetic energy 

 in general are no more modes of 

 motion than potential energy of 

 every kind is a mode of rest." 

 "Heat is not the mere motions, 

 but the energy of these motions." 

 There is no doubt that the terms 

 force and motion can be used in 

 very different meanings, and that 

 the early expounders of the me- 

 chanical theory of heat have not 

 been always consistent in the use 

 of words ; though their ideas, wher- 

 ever they appeared in mathematical 



expressions, were definite enough. 

 A good deal of vagueness has ac- 

 cordingly crept into popular text- 

 books and into philosophical treat- 

 ises, and criticisms such as those 

 of Prof. Tait have been useful in 

 helping us towards clearer con- 

 ceptions. We shall come across 

 more of these instances in the next 

 chapter when dealing with the 

 gradual evolution of the conception 

 of energy. 



2 See Lord Kelvin's abstract of 

 lecture, ' ' Elasticity viewed as 

 possibly a Mode of Motion," 1881; 

 'Popular Lectures,' &c., vol. i. p. 

 142. " I have always admired it " 

 (viz. , Tyndall's title) ; " I have long 

 coveted it for elasticity, and now, 

 by kind permission of its Inventor, 

 I have borrowed it for this dig- 



