38 CROONIAN LECTURES 



his science to his dependence on the certainty 

 of gravitation applied by the balance, so may 

 the physical philosopher expect to find the 

 greatest security and the utmost aid in the 

 principle of the conservation of force. All 

 that we have that is good and safe, as the 

 steam-engine, the electric telegraph, etc., wit- 

 ness to that principle. It would require a 

 perpetual motion, a fire without heat, heat 

 without a source, action without reaction, cause 

 without effect, or effect without a cause, to 

 displace it from its rank as a law of Nature." 



Finally, he says: "By admitting no hypo- 

 thesis, and believing in no assertion of any fact 

 opposed to the principle of the conservation 

 of force, the natural philosopher is prepared to 

 look for effects and conditions as yet unknown, 

 and the way for him is open to any degree of 

 development of the consequences and relations 

 of power. By denying this principle, he opposes 

 a dogmatic barrier to improvement ; whilst, by 

 admitting it, he has a fresh stimulus to investi- 

 gation and a pilot to human science." (P. 450.) 



In my next lectures, I shall show you how 

 far the three stages of ideas on the separability 

 of matter and force can be recognised in the 



