EXAMPLES OP THE EXPLANATION OF LAWS. 537 



quantity of which the vigorous action of the human system 

 partly depends. 



The instances of new theories agreeing with and explaining 

 old empiricisms, are innumerable. All the just remarks made 

 by experienced persons on human character and conduct, are 

 so many special laws, which the general laws of the human 

 mind explain and resolve. The empirical generalizations on 

 which the operations of the arts have usually been founded, 

 are continually justified and confirmed on the one hand, or 

 corrected and improved on the other, by the discovery of the 

 simpler scientific laws on which the efficacy of those operations 

 depends. The effects of the rotation of crops, of the various 

 manures, and other processes of improved agriculture, have 

 been for the first time resolved in our own day into known laws 

 of chemical and organic action, by Davy, Liebig, and others. 

 The processes of the medical art are even now mostly empirical : 

 their efficacy is concluded, in each instance, from a special and 

 most precarious experimental generalization : but as science 

 advances in discovering the simple laws of chemistry and phy 

 siology, progress is made in ascertaining the intermediate links 

 in the series of phenomena, and the more general laws on 

 which they depend; and thus, while the old processes are 

 either exploded, or their efficacy, in so far as real, explained, 

 better processes, founded on the knowledge of proximate 

 causes, are continually suggested and brought into use.* 

 Many even of the truths of geometry were generalizations 

 from experience before they were deduced from first prin- 



* It was an old generalization in surgery, that tight bandaging had a ten 

 dency to prevent or dissipate local inflammation. This sequence, being, in the 

 progress of physiological knowledge, resolved into more general laws, led to 

 the important surgical invention made by Dr. Arnott, the treatment of local 

 inflammation and tumours by means of an equable pressure, produced by a 

 bladder partially filled with air. The pressure, by keeping back the blood from 

 the part, prevents the inflammation, or the tumour, from being nourished : in 

 the case of inflammation, it removes the stimulus, which the organ is unfit to 

 receive ; in the case of tumours, by keeping back the nutritive fluid, it causes 

 the absorption of matter to exceed the supply, and the diseased mass is 

 gradually absorbed and disappears. 



