470 INDUCTION. 



of necessity, moves towards the west as the moon 

 followed by the nearer of the tide waves advances 

 towards the east: and yet both these motions are 

 equally effects of the moon's motion. 



That the oscillations of the pendulum are caused 

 by the earth, is proved by similar evidence. Those 

 oscillations take place between equidistant points on 

 the two sides of a line, which, being perpendicular to 

 the earth, varies with every variation in the earth's 

 position, either in space or relatively to the object. 

 Speaking accurately, we only know by the method 

 now characterized, that all terrestrial bodies tend to 

 the earth, and not to some unknown fixed point lying 

 in the same direction. In every twenty-four hours, 

 by the earth's rotation, the line drawn from the body 

 at right angles to the earth coincides successively 

 with all the radii of a circle, and in the course of six 

 months the place of that circle varies by nearly two 

 hundred millions of miles ; yet in all these changes of 

 the earth's position, the line in which bodies tend to 

 fall continues to be directed towards it : which proves 

 that terrestrial gravity is directed to the earth, and 

 not, as was once fancied by some, to a fixed point of 

 space. 



The method by which these results were obtained, 

 may be termed the Method of Concomitant Variations : 

 it is regulated by the following canon : 



FIFTH CANON. 



Whatever phenomenon varies in any manner when- 

 ever another phenomenon varies in some particular 

 manner, is either a cause or an effect of that phenomenon, 

 or is connected with it through some fact of causation. 



The last clause is subjoined, because it by no 

 means follows when two phenomena accompany each 



