44 GENERAL PREFACE TO 



observation than to any other which is used in modern scientific 

 language. 



Of some classes of these instances collections are to be made 

 for their own sake, and independently of any investigation into 

 particular natures. Such, for instance, are the instantise con- 

 formes ; Bacon's examples of which are mostly taken from com- 

 parative anatomy. One of them is the analogy between the 

 fins of fishes, the feet of quadrupeds, and the feet and wings of 

 birds ; another, the analogy of the beak of birds and the teeth 

 of other animals, &C. 1 



The other classes of prerogative instances have especial re- 

 ference to particular investigation, and are to be collected when 

 individual tables of comparence are formed. 



It would seem from this that the theory of prerogative in- 

 stances is intended to guide us in the formation of these tables. 

 But it is difficult to see how the circumstances which give any 

 instance its prerogative could have been appreciated a priori. 

 iAn instantia crucis 2 , to take the most celebrated of all, has its 

 distinguishing character only in so far as it is viewed with re- 

 ference to two contending hypotheses. In forming at the 

 outset of an inquiry the appropriate tables, nothing would 

 have led the interpreter to perceive its peculiar value. 



This theory, whatever may be its practical utility, may sup- 

 ply us with new illustrations of the importance in Bacon's 

 method of the process of exclusions. 



At the head of the list and placed there, we may presume, 

 from the importance of the end which they promote stand the 

 instantise solitariae, whose prerogative it is to accelerate the 

 Exclusiva. 3 These are instances which exhibit the given nature 

 in subjects which have nothing in common, except that nature 

 itself, with the other subjects which present it to us. Thus the 

 colours shown by the prism or by crystals are a solitary instance 

 of colour, because they have nothing in common with the fixed 

 colours of flowers, gems, &c. Whatever therefore is not in- 

 dependent of the particular constitution of these bodies must be 

 excluded from the form of colour. 



Next to the instantiae solitarias are placed the instantiaa 

 migrantes, which show the given nature in the act of appearing 



1 Nov. Org. ii. 27. It does not seem that Bacon added much to whut he found in 

 Aristotle on the subject of these analogies. 



8 Nov. Org. ii. 36. 3 Nov. Org. ii. 22. 



