THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 117 



pours on all the attempts which he passes under review, that 

 they seek " to prove the Second Law, about v/hich we know 

 something, by means of molecules, about which we know much 



less." * 



55. 



It would appear that even the partial success which has 

 been reached in the attempt to unify by means of dynamical 

 concepts alone the phenomena which lie in the old provinces of 

 Heat and Mechanics, is dependent, at least in the present state 

 of science, upon the use of methods which (in Professor J. J. 

 Thomson's words)! " do not require an intimate knowledge of 

 the system to which they are applied." If we are modest 

 enough to abandon the hope that we may, by the application of 

 dynamics, "discover the properties of such systems [as are 

 investigated in physics] in an altogether d priori fashion," we 

 may yet most usefully employ dynamical methods " to predict 

 their behaviour under certain circumstances after having 

 observed it under others."! "The way in which dynamical 

 considerations may enable us to connect phenomena in different 

 branches in physics," is illustrated by Professor Thomson in the 

 following manner : 



"Let us suppose that we have a number of pointers on a 

 dial, and that behind the dial the various pointers are con- 

 nected by a quantity of mechanism of the nature of which we 

 -are entirely ignorant. Then if we move one of the pointers, 

 A, say, it may happen that we set another, B, in motion. 



" If, now, we observe how the velocity and position of B 

 depend on the velocity and position of A, we can by the aid 

 of dynamics foretell the motion of A when the velocity and 

 position of B are assigned, and we can do this even though we 

 are ignorant of the nature of the mechanism connecting the 



* Op. dt., p. 121. 



t J. J. Thomson, Applications, p. 8. 



| Thomson, op. cit., p. 5. 



