382 INDUCTION. 



Scientifically speaking, that title is employed in a 

 more restricted sense, to designate the uniformities 

 when reduced to their most simple expression. Thus 

 in the illustration already employed, there were seven 

 uniformities ; all of which, if considered sufficiently 

 certain, would, in the more lax application of the 

 term, be called laws of nature. But of the seven, 

 three alone are properly distinct and independent ; 

 these being pre-supposed, the others follow of course : 

 the three first, therefore, according to the stricter 

 acceptation, are called laws of nature, the remainder 

 not ; because they are in truth mere cases of the 

 three first ; virtually included in them ; said, there- 

 fore, to result from them : whoever affirms those 

 three has already affirmed all the rest. 



To substitute real examples for symbolical ones, 

 the following are three uniformities, or call them 

 laws of nature : the law that air has weight, the law 

 that pressure on a fluid is propagated equally in all 

 directions, and the law that pressure in one direction, 

 not opposed by an equal pressure in the contrary 

 direction, produces motion, which does not cease 

 until equilibrium is restored. From these three uni- 

 formities we should be able to predict another uni- 

 formity, namely, the rise of the mercury in the 

 Torricellian tube. This, in the stricter use of the 

 phrase, is not a law of nature. It is a result of laws 

 of nature. It is a case of each and every one of the 

 three laws ; and is the only occurrence by which they 

 could all be fulfilled. If the mercury were not sus- 

 tained in the barometer, and sustained at such a height 

 that the column of mercury were equal in weight to a 

 column of the atmosphere, of the same diameter; 

 here would be a case, either of the air not pressing 

 upon the surface of the mercury with the force which 



