402 INDUCTION. 



must be an earth : and accordingly it is often said, 

 that the fall of a stone is caused by the earth ; or by 

 a power or property of the earth, or a force exerted 

 by the earth, all of which are merely roundabout ways 

 of saying that it is caused by the earth ; or, lastly, 

 the earth's attraction ; which also is only a technical 

 mode of saying that the earth causes the motion, with 

 the additional particularity that the motion is towards 

 the earth, which is not a character of the cause, but 

 of the effect. Let us now pass to another condition. 

 It is not enough that the earth should exist ; the 

 body must be within that distance from it, in which 

 the earth's attraction preponderates over that of any 

 other body. Accordingly we may say, and the ex- 

 pression would be confessedly correct, that the cause 

 of the stone's falling is its being within the sphere of 

 the earth's attraction. We proceed to a further con- 

 dition. The stone is immersed in water : it is there- 

 fore a condition of its reaching the ground, that its 

 specific gravity exceed that of the surrounding fluid, 

 or in other words that it surpass in weight an equal 

 volume of water. Accordingly, any one would be 

 acknowledged to speak correctly who said, that the 

 cause of the stone's going to the bottom is its exceed- 

 ing in specific gravity the fluid in which it is immersed. 

 Thus we see that each and every condition of 

 the phenomenon may be taken in its turn, and, 

 with equal propriety in common parlance but with 

 equal impropriety in scientific discourse, may be 

 spoken of as if it were the entire cause. And in 

 practice that particular condition is usually styled 

 the cause, whose share in the matter is superficially 

 the most conspicuous, or whose requisiteness to 

 the production of the effect we happen to be insist- 

 ing upon at the moment. So great is the force of 



