40 MATTER AND FOECE, IN PHYSICAL PHENOMENA. 



The word Force, with all the adjuncts that have been 

 impressed upon it, still looms before us, as a mysterious 

 symbol, rather than an intelligible reality. 



What I have said as to heat applies alike to other 

 forms or agents of force, into which it is more or less 

 directly convertible. The manifestations of these powers 

 are in matter, but we cannot affirm that they are iden- 

 tical with or originate in matter. In truth, the material 

 theory of heat, so ably expounded by Tyndall, em- 

 bodies more of proof than we can bring to any other 

 of the so-called natural forces. In chemical actions, 

 indeed, including crystallisation, we interpret the phe- 

 nomena through atomic motions and changes, strictly 

 defined by laws of number, proportion and figure. 

 Though we know that light as an agent pervades and 

 affects matter in its intimate atomic structure, the evi- 

 dence here is less complete than that regarding heat. 

 Of electricity as a force I have spoken in another of 

 these papers. In all these innumerable and subtle 

 phenomena of attraction, repulsion, polarisation, &c. 

 we see a general concurrence of actions, derived from 

 what we must call force, in default of other and better 

 name. If this be primarily resident in the atoms them- 

 selves, still must we recognise it by some name as a 

 principle of motion and change. 



Mechanical force, whether derived from gravita- 

 tion or other cause, has been a favourite topic even 

 from the infancy of science partly from its practical 

 value, partly because lending itself to certain abstruse 

 conceptions, grateful to the genius of ancient philo- 

 sophy ; and indeed descending, by a sort of compulsion, 



