130 Mr Glover on Forms of Induction. 



the mind endeavours to supply this deficiency in its evidence 

 mth respect to the actions of Nature, by feigning the existence 

 of such principles of essentiality, the want of which it must per- 

 ceive. And thus the necessary defect in inductive evidence, which 

 many writers on logic have misplaced, arises from no logical 

 fiction or physical impropriety in regarding one individual of 

 a class as a specimen of its brethren, but from an imperfection 

 in the media of communication between the understanding and 

 external nature. 



Instances which possess an organization so highly organized 

 as to admit of them being taken for specimens of the class to 

 which they belong, are termed by Bacon prerogative. And it 

 is the chief merit of his philosophy, that he perceived their place 

 and their power.* He has not, however, given any clear general 

 definition of them, but abundant examples to shew their uti- 

 lity ; and also a classification of individual instances, in which 

 all the varieties of prerogative facts are minutely described. 

 Here we shall consider them in general, since our object leads 

 us to view them, not as they differ among themselves, but ac- 

 cording to their place in the general theory of induction. 



A good illustration of a prerogative fact is afforded by the 

 famous experiment of the soap bubble, by which Newton dis- 

 covered, in a single instance, the proximate structure upon 

 which the various colours of all bodies are dependent. This 

 instance is composed of several parts. In the first place, an 

 appearance of coloured rings was observed upon the surface of 

 the soap bubble, and their order of appearance in some degree 

 estimated and compared with the thickness of the bubble at 

 different parts ; in the second place, the instance was varied by 

 using a layer of water placed between the object glass of a te- 

 lescope and a flat surface ; thus the thickness of the layer of 

 water could be measured, where the different rings appeared, 

 and also the order of their array became more regular ', in the 

 third place, it tvas found that the condition of the ambient 

 body did not affect the order of appearance, although it did the 

 strength and variety of the colours ; in the next place, it was 

 found that different transparent bodies would not, under the 



* Nov. Org. P. 2, s. 2, Aph. 22. 



