422 BACON 



they are cast into the fire, the aqueous spirit escapes with a 

 crackling noise before flame is produced, which also happens in 

 a less degree in stiff leaves, from the escape of the aqueous part 

 before the oily part has caught fire. This is more particularly 

 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, when 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 not 

 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 own nature, of duration, but is subjected 

 to some violence from the contrary natures which surround it, 

 and is destroyed. 



We may therefore adopt the following instance of the cross. 

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

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

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

 extinction takes place at the sides, where the flame is com- 

 pressed by the air, and is ill at ease ; but the centre of the flame, 

 which is untouched by the air and surrounded by flame, con- 

 tinues the same, and is not extinguished until compressed by 

 degrees by the air attacking it from the sides. All flame, there- 

 fore, is pyramidal, having its base near the source, and its vertex 

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

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

 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 are 

 clearly heterogeneous. 



The instance of the cross will be more accurate, if the ex- 

 periment can be made by flames of different colors. Take, 

 therefore, a small metal sconce, and place a lighted taper in it, 

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

 wine 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 



