EMPIRICAL LAWS. 305 



convinced that it is contingent upon something ; because the homoge- 

 neousness of tlie antecedent with the consequent, the close resemblance 

 of the seedling to the tree in all respects except magnitude, and the 

 graduality of the growth, so exactly resembling the progi'essiv^ly accu- 

 mulating effect produced by the long action of some one cause, leave 

 scarcely a possibility of doubting that the seedling and the tree are 

 really two terms in a series of that description, the first tenn of which 

 is yet to seek. The conclusion is further confirmed by this, that we 

 are able to prove by strict induction the dependence of the gi'owth of 

 tlie tree, and even of the continuance of its existence, upon the con- 

 tinued repetition of certain pi-ocesses of nutrition, the rise of the sap, 

 the absorptions and exhalations by the leaves, &:c., and the same ex- 

 periments would probably prove to us that the growth of the tree is 

 the accumulated sum of the effects of these continued processes, were 

 we not, for want of sufficiently microscopic eyes, unable to obseiTe 

 correctly and in detail what those effects are. 



CHAPTER XVI. ^ 



OF EMPIRICAL LAWS. 



§ 1. Experimental philosophers usually give the name of Empirical 

 Laws to those uniformities which observation or experiment has shown 

 to exist, but upon which they hesitate to rely in cases varying much 

 from those which have been actually observed, for want of seeing any 

 reason why such a law should exist. It is implied, therefore, in the 

 notion of an empirical law, that it is not an ultimate law ; that if true 

 at all, its truth is capable of being, and requires to be, accounted for. 

 It is a derivative law, the derivation of which is not yet known. To 

 state the explanation, the why of the empuical law, would be to state 

 the laws from which it is derived; the ultimate causes upon which 

 it is contingent. And if we knew these, wc should also know what 

 are its limits ; under what conditions it .would cease to be fulfilled. 



The periodical return of eclipses, as originally ascertained by the 

 persevering obsei-vation of the early eastern astronomers, was an em- 

 pirical law, until the general laws of the celestial motions had 

 accounted for it. The following are empirical laws still waiting to be 

 resolved into the simpler laws from which they are derived. The local 

 laws of the flux and reflux of the tides in different places : the succes- 

 sion of certain kinds of weather to certain appearances of sky : the ap- 

 parent exceptions to the almost universal tmth that bodies expand by 

 increase of temperaturej: the law that breeds, both animal and vegeta- 

 ble, are improved by crossing: that gases have a strong tendency to 

 permeate animal membranes : that opium and alcohol intoxicate: that 

 sub:>tanccs containing a veiy high proportion of nitrogen (such as hy- 

 drocyanic acid and morphia) are powcrfid poisons: that when different 

 metals are fused together the alloy is harder than the various elements: 

 that the number of atoms of acid required to neutralize one atom of 

 any base, is equal to the number of atoms of oxygen in the base : that 



