Ofl NOYUM OKGANUM. [BOOK It. 



observed in quicksilver, which is not improperly called mineral 

 water, and which, without any inflammation, nearly equals the 

 force of gunpowder by simple explosion and expansion, and is 

 said, vhen mixed with gunpowder, to increase its force. 



Again, let the required nature be the transitory nature of 

 flame and its momentaneous extinction ; for to us the nature of 

 flame does not appear to be fixed or settled, but to be generated 

 from moment to moment, and to be every instant extinguished ; 

 it being clear that those flames which continue and last, do net 

 owe their continuance to the same mass of flame, but to a con 

 tinued succession of new flame regularly generated, and that the 

 same identical flame does not continue. This is easily shown by 

 removing the food or source of the flame, when it at once goes out. 

 We have the two following cross- ways with regard to this nature : 

 This momentary nature either arises from the cessation of the 

 cause which first produced it, as in light, sounds, and violent 

 motions, as they are termed, or flame may be capable, by its ow i 

 nature, of duration, but is subjected to some violence from tha 

 contrary natures which surround it, and is destroyed. 



We may therefore adopt the following instance of the cros*. 

 We see to what a height the flames rise in great conflagrations ; 

 for as the base of the flame becomes more extensive, its vertet 

 is more lofty. It appears, then, that the commencement of th-3 

 extinction takes place at the sides, where the flame is compresse&amp;gt;l 

 by the air, and is ill at ease j but the centre of the flame, whic i 

 is untouched by the air and surrounded by flame, continues tha 

 same, and is not extinguished until compressed by degrees by 

 the air attacking it from the sides. All flame, therefore, is pyra 

 midal, having its base near the source, and its vertex pointed 

 from its being resisted by the air, and not supplied from tli3 

 source. On the contrary, the smoke, which is narrow at tha 

 base, expands in its ascent, and resembles an inverted pyramid, 

 because the air admits the smoke, but compresses the flame ; for 

 let no one dream that the lighted flame is air, since they axa 

 clearly heterogeneous. 



The instance of the cross will be more accurate, if the expe 

 riment can be made by flames of different colours. Take, there 

 fore, a small metal sconce, and place a lighted taper in it, the:i 

 put it in a basin, and pour a small quantity of spirits of win* 

 round the sconce, so as not to reach its edge, and light the spirit . 

 Now the flame of the spirit will be blue, and that of the taper 

 yellow ; observe, therefore, whether the latter (which can easily 

 be distinguished from the former by its colour, for flames do not 

 mix immediately, as liquids do) continue pyramidal, or tend 

 more to a globular figure, since there is nothing to destroy or 

 compress it. If the latter result be observed, it must be con 

 sidered as settled, that flame continues positively the same, whilst 



