OF NATURAL PHILOSOPHY. 187 



in themselves, or of the attraction of the earth " by 

 the corporeal mass thereof, as by a collection of 

 bodies of the same nature." If it be so, he says, 

 " it will follow that the nearer all bodies approach 

 to the earth, the stronger and with the greater 

 force and velocity they will tend to it; but the 

 farther they are, the weaker and slower:" and his 

 experiment consists in comparing the effect of a 

 spring and a weight in keeping up the motions of 

 two " clocks," regulated together, and removed al- 

 ternately to the tops of high buildings and into the 

 deepest mines. By clocks he could not have meant 

 pendulum clocks, which were not then known, (the 

 first made in England was in 1662,) but^y-clocks, 

 so that the comparison, though too coarse, was not 

 contrary to sound mechanical principles. In short, 

 its principle was the comparison of the effect of a 

 spring with that of a weight, in producing certain 

 motions in certain times, on heights and in mines. 

 Now, this is the very same thing that has really been 

 done in the recent experiments of professors Airy 

 and Whewell in Dolcoath mine: a pendulum (a 

 weight moved by gravity) has been compared with 

 a chronometer balance, moved and regulated by a 

 spring. In his 37th aphorism, Bacon also speaks of 

 gravity as an incorporeal power, acting at a distance, 

 and requiring time for its transmission ; a consider- 

 ation which occurred at a later period to Laplace, 

 in one of his most delicate investigations. 



(197.) A well chosen and strongly marked cru- 

 cial instance is, sometimes, of the highest import- 

 ance ; when two theories, which run parallel to each 

 other (as is sometimes the case) in their explan- 



