Remarks on Inertia. £3 



nication of motion ; and we know this much by experiment 

 only ; and all beyond is mere conjecture. 



There is another passage that immediately follows Profes- 

 sor F's speculations on the causes of inertia, which savours 

 still more of the doctrine of occult causes : " The force of in- 

 ertia, therefore, is, properly speaking, the means of the com- 

 munication of motion from one body to another."* Profes- 

 sor F. however, is not alone in this position : " Itaque con- 

 cludendum nullam esse vim qua motus communicetur, cum 

 nulla sit vis inertiae."t " La fuerza de inercia es un medio 

 para que los cuerpos se comuniquen el movimiento unos a 

 otros."t Now will any person, after a moments reflection, 

 pretend to say, that he knows the means by which motion is 

 communicated from one body to another ? — why a body in 

 motion striking against another, should impart its motion, or 

 how this is done ? We presume not : We believe that no 

 person has ever been able to point out the connexion be- 

 tween cause and effect, however indisputable the existence 

 of such a connexion may be ; at least we have not heard 

 such a discovery announced ; although the squaring of the 

 circle, and the discovery of perpetual motion, are not unfre- 

 quent in our day. What then is the extent of our knowledge as 

 regards the communication of motion? We know that matter 

 is inert, and cannot move itself; and consequently that a force 

 is necessary : but no human mind can explain the connecting 

 link between the application of the force and the reception of 

 motion by the body. A certain body is at rest : it is struck by 

 another body in motion, and immediately also commences 

 moving. The fact we know ; but the rationale of the fact is 

 beyond the powers of the mightiest minds. How then do wri- 

 ters prove that inertia is the means of the communication of 

 motion ? None of those, quoted above, have attempted this 

 except Bails ; who says " no podriamos concebir como se 

 podria comunicar movimiento alguno a un cuerpo que no se 

 nos resistiese."|| The best reason then which has been 

 given, is that we cannot conceive of the thing otherwise, and 

 therefore it is so. But unless we are greatly mistaken, the 



* Cambridge Mechanics, p. 179. 



t R. Cotes, prcefatio in Lee. Edit. Newtoni Princip. 



\ Elementos de Matematica porD. Benito Bails, vol. 4, p. 9. 



|| Elementos de Matematica, Prologo, vol. 4, p. 7. 



