118 THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 



two pointers." As the generalization of this example we read 

 that " the observation of the motion of B when that of A is 

 assigned may be taken to represent the experimental investiga- 

 tion of some phenomenon in Physics ; while the deduction by 

 dynamics of the motion of A when that of B is assigned may 

 represent the prediction ... of a new phenomenon which is 

 a consequence of the one investigated experimentally."* 



For the application of the method contemplated which is 

 a development of Hamilton's or Lagrange's principle it is 

 only necessary to suppose that the system is possessed of 

 a constant amount of energy which expresses itself by 

 various ''co-ordinates," a term, originally of a strictly 

 limited geometrical significance, which was extended to any 

 quantities which can be used to determine the position of a 

 body in spacej or the spatial configuration of the parts of a 

 systemj and in the present connection is further extended to 

 elements which " fix the configuration " of the system in a wider 

 sense, such as elastic strains, electrical and magnetic phenomena. 

 This constant quantity of energy may be regarded either as the 

 sum of the " kinetic " and " potential " energies of the system, 

 or (in view of the fact that potential energy is a somewhat 

 unsatisfactory term, corresponding directly to nothing Objec- 

 tive^ as the sum of the kinetic energies of the given system 

 (determined by the "positional co-ordinates") and of sub- 

 sidiary connected systems such as the ether (determined by 

 " kinosthenic " or " ignored " co-ordinates). It is clear that 

 terms in this expression for the energy of the system may be 

 contributed by each of the co-ordinates that fix its configura- 

 tion, and that the coefficients of such terms may involve any 

 of the other co-ordinates, and possibly more than one at the 



* Thomson, op. cit., p. 6. Cf. Eayleigh, Theory of Sound, pp. 71 

 and 75. 



t Routh, Rigid Dynamics, i, p. 57. 



1 Rayleigli, op. cit., p. 67. 



Cf. Bradley, Appearance and Reality, pp. 384 et seq. 



