162 NOVUM ORGANUM 



migration, 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 sub 

 jects; 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 understand 

 ing with a false notion of the form from the appearance of 

 such cause, which is never more than a vehicle or convey 

 ance 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 toward 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 dimin 

 ishing of the parts of the glass and water and the insertion 

 of air. Yet this is no slight progress toward discovering 



