'200 DISCOURSE ON THE STUDY 



mathematical expression. Such a case, for instance, 

 is the elliptic motion of a planet, which is a general 

 proposition including the statement of an infinite 

 number of particular places, in which the laws of its 

 motion allow it to be some time or other found, and 

 for which, of course, the law of force must be so 

 assumed as to account. 



(212.) With regard to the first process of the 

 three above enumerated, it is in fact an induction 

 of the kind described in 185.; and all the re- 

 marks we there made on that kind of induction 

 apply to it in this stage. The direct assumption 

 of a particular hypothesis has been occasionally 

 practised very successfully. As examples, we may 

 mention Coulomb's and Poisson's theories of elec- 

 tricity and magnetism, in both which, phenomena 

 of a very complicated and interesting nature 

 are referred to the actions of attractive and re- 

 pulsive forces, following a law similar in its expres- 

 sion to the law of gravitation. But the difficulty 

 and labour, which, in the greater theories, always 

 attends the pursuit of a fundamental law into its 

 remote consequences, effectually precludes this me- 

 thod from being commonly resorted to as a means 

 of discovery, unless we have some good reason, 

 from analogy or otherwise, for believing that the 

 attempt will prove successful, or have been first 

 led by partial inductions to particular laws which 

 naturally point it out for trial. 



(213.) In this case the law assumes all the cha- 

 racters of a general phenomenon resulting from an 

 induction of particulars, but not yet verified by com- 

 parison with all the particulars, nor extended to all 



