576 INDUCTION. 



operations of the arts have usually been founded, are 

 continually justified and confirmed on the one hand, 

 or rectified and improved on the other, by the disco- 

 very 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 the 

 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 and 

 Liebig. The processes of the healing art are even now 

 mostly empirical ; their efficacy is concluded, in each in- 

 stance, from a special and most precarious experimental 

 generalization : but as science advances in discovering 

 the simple laws of chemistry and physiology, 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, 

 improved 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 principles. The quadra- 

 ture of the cycloid was first effected by measurement, 



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

 had a tendency to prevent or dissipate local inflammations. This se- 

 quence being, in the progress of physiological knowledge, resolved into 

 more general laws, led to the important surgical invention recently 

 made by Dr. Arnott, the treatment of local inflammation and 

 tumours by means of an equable pressure, produced by a bladder par- 

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

 the part, prevents tKe 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. 



