NOVUM ORGANUM. 127 



reduce affirmation, or the form itself to a narrow compass. 

 For the form must be something conferred by this migra 

 tion, or on the contrary removed and destroyed by it. And 

 although all exclusion advances affirmation, yet this takes 

 place more directly in the same than in different subjects. 

 But if the form (as it is quite clear from what has been 

 advanced) exhibit itself in one subject it leads to all. The 

 more simple the migration is, the more valuable is the 

 instance. These migrating instances are, moreover, very 

 useful in practice, for since they manifest the form, coupled 

 with that which causes or destroys it, they point out the 

 right practice in some subjects, and thence there is an easy 

 transition to those with which they are most allied. There 

 is, however, a degree of danger which demands caution, 

 namely, lest they should refer the form too much to its 

 efficient cause, and imbue or, at least, tinge the under 

 standing with a false notion of the form from the appear 

 ance of such cause ; which is never more than a vehicle or 

 conveyance of the form. This may easily be remedied by 

 a proper application of exclusion. 



Let us then give an example of a migrating instance. 

 Let whiteness be the required nature. An instance which 

 passes towards generation is glass in its entire and in its 

 powdered state ; or water in its natural state, and when 

 agitated to froth. For glass when entire, and water in its 

 natural state, are transparent and not white, but powdered 

 glass and the froth of water are white and not transparent. 

 We must inquire, therefore, what has happened to the glass 

 or water in the course of this migration. For it is manifest 

 that the form of whiteness is conveyed and introduced by 

 the bruising of the glass, and the agitation of the water. 

 But nothing is found to have been introduced but a dimi 

 nishing of the parts of the glass and water, and the inser 

 tion of air. Yet this is no slight progress towards disco 

 vering the form of whiteness, namely, that two bodies in 

 themselves more or less transparent (as air and water, or air 

 and glass), when brought into contact in minute portions 

 exhibit whiteness, from the unequal refraction of the ravs 

 of light. 



But here we must also give an example of the danger 

 and caution of which we spoke. For instance; it will 

 readily occur to an understanding perverted by efficients, 

 that air is always necessary for producing the form of 

 whiteness, or that whiteness is only generated by transpa 

 rent bodies, which suppositions are both false, and proved 



