208 NOVUM ORGANUM 



have the two following crossways 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 capa 

 ble, 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 compressed by the air, and is ill 

 at ease; but the centre of the flame, which is untouched by 

 the air and surrounded by flame, continues the 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 sup 

 plied 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 

 experiment 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, 



