36 MATTER AND FORCE, IN PHYSICAL PHENOMENA. 



towards the latter belief. Heat, for instance, is inter- 

 preted (long ago by partial conjecture) as one mode of 

 motion in the molecules of bodies, communicable in the 

 same form, or convertible into other forms of power, 

 with an exact mensurable equivalence of each and all. 

 This convertibility and equivalence lead us forward 

 to what seems to be a great natural truth. They ex- 

 press the principle, that force, whatever it intrinsically 

 be, is, like matter, never lost in the world perhaps we 

 might say in the universe around us. Translated or 

 altered in mode of action it may be, but not annihi- 

 lated. This is a vast and bold conclusion, yet so far 

 pressed upon us by experimental facts, that it cannot 

 logically be evaded. It moreover connects together 

 the different kinds or exponents of force by a strong 

 natural link one expressive of some higher unity, to 

 which science is now more than ever tending. Heat, 

 electricity, chemical affinities, and the mechanical 

 powers come more especially under this connexion ; 

 and are subjected to formulae, which not only expound 

 but predict results. The indestructibility of matter is 

 an ancient tenet of philosophy 1 that of force may be 

 called a discovery of our own time ; indicated indeed 

 by Newton, as a result of reason, but now amply at- 

 tested by experimental research. 



1 We gather from Plutarch a dogma of Pythagoras : 



. . piiaiQ ovdttb^ iarlv tKaarov, 

 'AXAu fioi'ov fjiiit; Tf Cid\\a%i Tt /itylrrwr. 



To this may be added the well-known lines of Lucretius : 

 ' Haud igitur redit ad Nihilum res ulla, sed omnes 

 Discidio redeunt in corpora Material ; ' 



and elsewhere he states that the Summa of Matter remains ever the 

 same. 



