498 INDUCTION. 



usually have exceptions ; but principles of science, or in 

 other words, laws of causation, have not. " What is thought 

 to be an exception to a principle," (to quote words used on 

 a different occasion,) " is always some other and distinct 

 principle cutting into the former; some other force which 

 impinges* against the first force, and deflects it from its 

 direction. There are not a law and an exception to that law, 

 the law acting in ninety-nine cases, and the exception in one. 

 There are two laws, each possibly acting in the whole hundred 

 cases, and bringing about a common effect by their conjunct 

 operation. If the force which, being the less conspicuous of 

 the two, is called the disturbing force, prevails sufficiently 

 over the other force in some one case, to constitute that case 

 what is commonly called an exception, the same disturbing 

 force probably acts as a modifying cause in many other cases 

 which no one will call exceptions. 



" Thus if it were stated to be a law of nature that all 

 heavy bodies fall to the ground, it would probably be said 

 that the resistance of the atmosphere, which prevents a balloon 

 from falling, constitutes the balloon an exception to that 

 pretended law of nature. But the real law is, that all heavy 

 bodies tend to fall ; and to this there is no exception, not even 

 the sun, and moon; for even they, as every astronomer knows, 

 tend towards the earth, with a force exactly equal to that 

 with which the earth tends towards them. The resistance of 

 the atmosphere might, in the particular case of the balloon, 

 from a misapprehension of what the law of gravitation is, be 

 said to prevail over the law ; but its disturbing efFuct is quite 

 as real in every other case, since though it does not prevent, 

 it retards the fall of all bodies whatever. The rule, and the 

 so-called exception, do not divide the cases between them ; 

 each of them is a comprehensive rule extending to all cases. 

 To call one of these concurrent principles an exception to 

 the other, is superficial, and contrary to the correct principles 



* It seems hardly necessary to say that the word impinge, as a general 

 term to express collision of forces, is here used by a figure of speech, and not 

 as expressive of any theory respecting the nature of force. 



