36 VIEWS OF HERSCHEL AND WHEWELL. 



but cease whenever that important function is 

 arrested ; as will be shown in subsequent parts of 

 this work.* 



But if it be true that caloric is perpetually 

 radiated from the sun and fixed stars into the 

 boundless regions of space, it must constitute an 

 infinite ocean of aethereal essence ; consequently, 

 there can be no such thing as a vacuum, which, 

 as Aristotle rightly observed, would destroy all 

 motion. Nor is it less obvious, that if caloric 

 be a self-active principle, and is every where 

 present, there can be no such condition of matter 

 as vis inertia, which literally means the power 

 of not acting. And that a single impulse is not 

 competent to maintain the unceasing motion of 

 planets and satellites, is evident from Newton's 



* Such facts have created very strong doubt in the minds of 

 philosophers in regard to the truth of Newton's first law of mo- 

 tion. For example, it is observed by Sir John Herschel that, 

 " to say matter has inertia, is only to say that the cause is ex- 

 pended in producing its effect, and that the same cause cannot 

 continue to produce its effect without renewal." (Nat. Philoso- 

 phy, sect. 234.) And it was humorously argued by the author of 

 Knickerbocker, that " as the projectile force has long since ceased 

 to operate, while its antagonist remains in undiminished potency, 

 the world ought, in strict propriety, to tumble into the sun." Nor 

 would it be difficult to demonstrate, that this catastrophe would 

 occur before it performed one fourth part of its annual revolution, 

 if the force of gravity were counteracted only by a single impulse 

 of equal force. Mr. Whewell also observes in his Bridgewater Trea- 

 tise on Astronomy, that " to say motion must continue the same 

 from one instant to another, because there is nothing to stop it, 

 seems to be taking refuge in words." But there is no one force 



