156 THE LIMITATIONS OF SCIENCE 



tion of matter is always proportional to the amount of 

 matter acting, and does not differ in any way from the 

 inertia of mass except in our method of apprehending 

 it. By inertia of matter is meant, that a body can be 

 changed from its previous condition of rest or motion 

 only by this material force. It is evident that he 

 regarded inertia as an inherent and inalienable prop- 

 erty of a body, independent of the influence of any 

 other body or ether, and forming the connecting link 

 between ourselves and the external world. Such being 

 the case, how may we decide what is the mass of any 

 particular body? If a number of individuals measure 

 experimentally a mass, or even if one of them measures 

 it several times, no two observations will agree. Which 

 observation gives the correct value? Newton would 

 have answered, none of them. Data of objective phe- 

 nomena can never be known exactly ; each value we ob- 

 tain approximates to the truth, and the approximation 

 is the closer, the greater the number so obtained and 

 the greater the care exercised. The final result must 

 be deduced from all the observations, according to a 

 well developed mathematical theory of errors. The 

 same reasoning was held to apply to observations on 

 the space dimensions of a body and on the time occur- 

 ring during any event. 



While the idea was advanced in this mechanics that 

 the position and motion of any body could be deter- 

 mined only from the position of some other body, 



