ancients founded their theory, certain it is, they 

 cleanly apprehended, that the planets revolved upon 

 their own axis. Heraclides of Pontus, and Ecphantus, 

 two celebrated Pythagoreans, intimated this truth 

 long ago, and made use of a very apt comparison to 

 convey their idea, saying, that the earth turned from 

 west to east, just as a wheel does upon its axis, or 

 centre. And Plato extended this observation from 

 the earth to the other planets ; for, according to At- 

 ticus, the Platonic, who explains his opinion, " to 

 that general motion which makes the planets describe 

 a circular course, he added another resulting from 

 their spherical shape, which made each of them move 

 about its own centre, whilst they performed the gene, 

 ral revolution of their course." Plotinus also ascribes 

 this sentiment to Plato, for speaking of him he says, 

 that besides the grand circular course observed by all 

 the stars in general, he thought, they each performed 

 another about their own centre. 



3. Cicero ascribes the same notion to Nicetas of 

 Syracuse, and quotes Theophrastus to warrant what 

 he advances ; this is he whom Diogenes Laertius 

 names Hycetas, whose opinion was, that the celerity 

 of the earth's motion about its own axis, and other- 

 wise, was the only cause of the apparent revolutions 

 of the heavenly bodies. 



4. Our secondary planet, the moon, gave the an- 

 cients an opportunity of displaying their penetration. 

 They early discovered that it hud no light of its own, 

 but shone with that which it reflected from the sun, 

 This, after Thales, was the sentiment of Anaxagoras 

 and of Empedocl? s, who thence accounted not only 

 for the mildness of its splendor, but the impcrceptibi. 

 lity of its heat ; which our experiments confirm : for 

 with all the aid of burning glasses, we have never yet 

 found it practicable to produce the least effect of heat 

 from any cpnibination of its rays. 



