226 NOVUM ORGANUM 



more easily observed by night than by day: for contempla 

 tions of this kind may be considered as carried on by 

 night, from the minuteness and perpetual burning of our 

 watch-light. 



The same must be attempted with inanimate objects, 

 which we have ourselves done by inquiring into the open 

 ing of liquids by fire. For the mode in which water ex 

 pands is different from that observed in wine, vinegar, or 

 verjuice, and very different, again, from that observed in 

 milk and oil, and the like; and this was easily seen by boil 

 ing them with slow heat, in a glass vessel, through which 

 the whole may be clearly perceived. But we merely men 

 tion this, intending to treat of it more at large and more 

 closely when we come to the discovery of the latent process; 

 for it should always be remembered that we do not here 

 treat of things themselves, but merely propose examples. 72 



XLII. In the nineteenth rank of prerogative instances 

 we will class supplementary or substitutive instances, which 

 we are also wont to call instances of refuge. They are such 

 as supply information, where the senses are entirely defi 

 cient, and we therefore have recourse to them when appro 

 priate instances cannot be obtained. This substitution is 



72 The itinerant instances, as well as frontier instances, are cases in which 

 we are enabled to trace the general law of continuity which seems to pervade 

 all nature, and which has been aptly embodied in the sentence, &quot;natura non 

 agit per saltum.&quot; The pursuit of this law into phenomena where its applica 

 tion is not at first sight obvious, has opened a mine of physical discovery, and 

 led us to perceive an intimate connection between facts which at first seemed 

 hostile to each other. For example, the transparency of gold-leaf, which per 

 mits a bluish-green light to pass through it, is a frontier instance between 

 transparent and opaque bodies, by exhibiting a body of the glass generally 

 regarded the most opaque in nature, as still possessed of some slight degree 

 of transparency. It thus proves that the quality of opacity is not a contrary 

 or antagonistic quality to that of transparency, but only its extreme lowest 

 degree. 



