ASTRONOMICAL HISTORY. 187 



forming a pyramid, is by an experiment of two flames of 

 different colours. There may also be very great difference 

 between the heat of flame in the heavenly bodies and in 

 ours. For the celestial flame expands freely and serenely, 

 as if in its own medium, ours, as if pent up in another, 

 blazes and rages. For all fire hedged about and impri 

 soned becomes fiercer. In fact the rays of the fires of 

 heaven themselves, after reaching denser and more impene 

 trable bodies, lose their mild quality and become more 

 scorching. Wherefore Aristotle ought not to have appre 

 hended Heraclitus s conflagration for his sphere, even al 

 though he had determined that the stars were real fires. 

 This question then may also be entertained subject to this 

 explanation. 



Another question follows, Whether the stars are kept 

 alive by due sustentation ? and also, whether they are in 

 creased, lessened, generated, extinguished? and in fact 

 one of the ancients supposed, from some vulgar observa 

 tion, that the stars were nourished as fire is, and fed upon 

 the waters, the sea, and the moisture of the earth, and were 

 sustained by their evaporations and exhalations, a notion 

 which seems unworthy to supply matter for any inquiry. 

 For such vapours fall far on this side the height of the 

 stars. Nor is there such a quantity of them as to supply 

 the waters and the land by rains and dews, and besides 

 suffice for repairing so many and so great heavenly orbs, 

 especially as it is evident that the earth and ocean have 

 not suffered diminution in the quantity of liquid for many 

 ages, so that it seems a necessary conclusion that as much 

 is replaced as is absorbed. Nor is the mode of supply so suit 

 able for the heavenly bodies as it is for our fire. For where 

 something perishes and is subtracted, there too something 

 is taken up and assimilated. This species of assimila 

 tion resembles the tartarizations of salts, and derives its 

 source from the contiguity all round it of opposite or dissi 

 milar substances. But in the consubstantial and interior 

 body of the stars nothing of the kind happens, no more 

 than in the bowels of the earth, but they preserve their 

 substance by the law of identity, not assimilation. But 

 with respect to the exterior surface of the starry bodies the 

 question is properly enough proposed ; whether they re 

 main in one and the same state, or steal from and even 

 taint the surrounding ether ? And in this sense we may 

 inquire also respecting the aliment of the stars. 



But it is proper here to subjoin the question with respect 



