330 NOVUM ORGANUM. 



xxii. Among Prerogative Instances we shall set forth first, Solitary 

 Instances. Now, Solitary Instances are those which exhibit the 

 Nature under investigation, in subjects which have nothing in common 

 with other subjects except that same Nature ; or again, those which 

 do not exhibit the Nature under investigation, in subjects which are 

 similar to other subjects in every respect except in that same Nature. 

 For it is manifest that Instances of this kind remove ambiguity, and 

 accelerate and strengthen Exclusion, so that a few of them are as 

 good as many. 



For example ; in the inquiry as to the Nature of Colour : prisms, 

 crystalline gems, which exhibit colours not only in themselves, but 

 when cast externally on a wall, are Solitary Instances. So also are 

 dews, c. For they have nothing in common with the fixed colours 

 of flowers, coloured gems, metals, wood, &c. except colour itself. 

 Whence we easily collect that colour itself is nothing but a modifica 

 tion of the image of incident and refracted Light, arising, in the 

 former case, from the different degrees of incidence ; in the latter, 

 from the various textures and structures of the bodies. These 

 Instances, then, are Solitary as regards resemblance. 



Again, in the same investigation, the distinct veins of white and 

 black in marble, and the variegations of colour in flowers of the same 

 species, are Solitary Instances; for the white and black of marble, 

 and the white and purple spots in the flower of the pink, agree in 

 almost every point except colour itself. Whence we easily gather 

 that colour has not much to do with the intrinsic Natures of any body, 

 but merely depends upon the groffer, and, as it were, mechanical 

 arrangement of the parts. And these Instances are Solitary as 

 regards difference. Both kinds we usually call Solitary Instances, or 

 Fcrince, borrowing the term from the astronomers. 



xxiii. Among Prerogative Instances we shall put in the second place, 

 Migrating Instances. Those, we mean, in which the Nature under 

 inquiry migrates towards generation, when it has not previously 

 existed, or else migrates towards corruption when it has previously 

 existed. And so in either such Instances are always twofold ; or 

 rather one Instance in motion or transit is carried out to the opposite 

 extreme. Instances of this kind not only accelerate and strengthen 

 Exclusion, but also force the Affirmative^ or the Form itself, into a 

 narrow compass. For the Form of a thing must necessarily be 

 something that is conferred by Migration of this kind ; or, on the 

 contrary, removed and destroyed by it. And although every Exclusion 

 promotes the Affirmative, yet this is more directly the case in the 

 same subject than in different ones. Now, Form (as is clear from 

 everything we have said), when it betrays itself in one case, leads 

 to its discovery in all. And the simpler the Migration, the more 

 valuable will be the Instance. Besides, Migrating Instances are of 

 great use in practice ; for when they set forth the Form coupled with 

 the Efficient or the Privative, they supply a clear direction for practice 

 in some cases, whence the passage is easy to the cases that come 

 next. There is, however, in these Instances a danger which requires 



