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glass), when brought into contact in minute portions, exhibit 

 whiteness from the unequal refraction of the rays 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 white- 

 ness is only generated by transparent bodies, which supposi- 

 tions are both false, and proved to be so by many exclusions ; 

 nay, it will rather appear (without any particular regard to air 

 or the like), that all bodies which are even in such of their parts 

 as affect the sight exhibit transparency, those which are uneven 

 and of simple texture whiteness, those which are uneven and of 

 compound but regular texture all the other colors except black, 

 but those which are uneven and of a compound irregular and 

 confused texture exhibit blackness. An example has been 

 given, therefore, of an instance migrating towards generation 

 in the required nature of whiteness. An instance migrating 

 towards corruption in the same nature is that of dissolving froth 

 or snow, for they lose their whiteness and assume the trans- 

 parency of water in its pure state without air. 



Nor should we by any means omit to state, that under mi- 

 grating instances we must comprehend not only those which 

 pass towards generation and destruction, but also those which 

 pass towards increase or decrease, for they, too, assist in the dis- 

 covery of the form, as is clear from our definition of a form and 

 the Table of Degrees. Hence paper, which is white when dry, 

 is less white when moistened (from the exclusion of air and 

 admission of water), and tends more to transparency. The rea- 

 son is the same as in the above instances. 



24. In the third rank of prerogative instances we will class 

 conspicuous instances, of which we spoke in our first vintage 

 of the form of heat, and which we are also wont to call corusca- 

 tions, or free and predominant instances. They are such as 

 show the required nature in its bare substantial shape, and at 

 its height or greatest degree of power, emancipated and free 

 from all impediments, or at least overcoming, suppressing, and 

 restraining them by the strength of its qualities ; for since every 

 body is susceptible of many united forms of natures in the con- 

 crete, the consequence is that they mutually deaden, depress, 

 break, and confine each other, and the individual forms are 

 obscured. But there are some subjects in which the required 

 nature exists in its full vigor rather than in others, cither from 

 the absence of any impediment, or the predominance of its qual- 

 ity. Such instances are eminently conspicuous. But even in 

 these care must be taken, and the hastiness of the understand- 

 ing checked, for whatever makes a show of the form, and forces 

 it forward, is to be suspected, and recourse must be had to 

 severe and diligent exclusion. 



