BOOK It.] APHORISMS. 451 



vegetable, We must (I say) consider what species of precept of 

 guide this person would prefer. And firstly, he will doubtless bo 

 anxious to DC shown some method that will neither fail in effect, 

 nor deceive him in the trial of it ; secondly, he will be anxious 

 that the prescribed method should not restrict him and tie him 

 down to peculiar means, and certain particular methods of acting ; 

 for he will, perhaps, be at loss, and without the power or oppor 

 tunity of collecting and procuring such means. Now if there bo 

 other means and methods (besides those prescribed) of creating 

 such a nature, they will perhaps be of such a kind as are in his 

 power, yet by the confined limits of the precept he will be de 

 prived of reaping any advantage from them ; thirdly, he will be 

 anxious to be shown something not so difficult as the required 

 effect itself, but approaching more nearly to practice. 



We will lay this down, therefore, as the genuine and perfect 

 rule of practice, that it should be certain, free, and preparatory, 

 or having relation to practice. And this is the same thing as the 

 discovery of a true form ; for the form of any nature is such, 

 that when it is assigned the particular nature infallibly follows. 

 It is, therefore, always present when that nature is present, and 

 universally attests such presence, and is inherent in the whole of 

 it. The same form is of such a character, that if it be removed 

 the particular nature infallibly vanishes. It is, therefore, absent, 

 whenever that nature is absent, and perpetually testiiies such 

 absence, and exists in no other nature. Lastly, the true form is 

 such, that it deduces the particular nature from some source of 

 essence existing in many subjects, and more known (as they 

 term it) to nature, than the form itself. Such, then, is our 

 determination and rule with regard to a genuine and perfect 

 theoretical axiom, that a nature be found convertible with a given 

 nature, and yet such as to limit the more known nature, in the 

 manner of a real genus. But these two rules, the practical and 

 theoretical, are in fact the same, and that which is most useful 

 in practice is most correct in theory. 



V. But the rule or axiom for the transformation of bodies is 

 of two kinds. The first regards the body as an aggregate or 

 combination of simple natures. Thus, in gold are united tho 

 following circumstances : it is yellow, heavy, of a certain weight, 

 malleable and ductile to a certain extent j it is not volatile, loses 

 part of its substance by fire, melts in a particular manner, is 

 separated and dissolved, by particular methods, and so of the 

 other natures observable in gold. An axiom, therefore, of this 

 kind deduces the subject from the forms of simple natures ; for 

 he who has acquired the forms and methods of superinducing 

 yellowness, weight, ductility, stability, deliquescence, solution, 

 ?jid the like, and their degrees and modes, will consider and 



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