VOL. XLVIII.] PHILOSOPHICAL TRANSACTIONS. 311 



and quotes both Theon and Cleomedes in confirmation of the opinion. Theon 

 perhaps had Cleomedes's words in view; but neither of these authors have cir- 

 cumstances enough to determine what eclipse in particular they meant. The 

 passage of Theon is in his chapter concerning the moon's parallax, where 

 he says that Hipparchus, being in doubt whether the sun had any parallax at all, 

 supposed, in the first book of his treatise concerning magnitudes and distances, 

 that the earth, in respect of the sun, was only a point ; whence, by means of an 

 eclipse there set down by him, he framed two distances of the sun, a less and a 

 greater. All then that is here said is, that the eclipse made use of by Hippar- 

 chus, was at the Hellespont ; but at Alexandria in Egypt a little more than 5 

 digits only. But he has neither given the asra of Nabonassar, the place of the 

 luminaries, nor any one circumstance besides, by which we might form any con- 

 clusion what year this eclipse was in. 



Cleomedes, who perhaps saw the same treatise of Hipparchus, is as uncircum- 

 stantial as Theon. He says only, that the diameter of the moon's shadow at the 

 earth is something more than 4000 stadia. By the quantity of obscuration he 

 mentions, this seems to have been the same eclipse with that quoted by Theon 

 from Hipparchus ; but as the place of observation in both these authors appears 

 to have been Alexandria in Egypt, it must have been after that place was built. 

 Consequently it was probably observed there by Hipparchus himself, and there- 

 fore could not have been the eclipse foretold by Thales. Besides, if this eclipse 

 was total on the banks of the Hellespont, I know not what reason there is for 

 supposing, that the battle between the Lydians and the Medes was fought there. 

 It should rather seem, that the engagement was on the confines of the two king- 

 doms : consequently in a more southern latitude, and in a longitude more to the 

 east of Alexandria, this eclipse could not have been total ; nor therefore (as He- 

 rodotus said it did) turn day into night. 



Sir Isaac Newton, in his chronology, likewise supposes the eclipse meant to 

 have been that in May, a. c. 585. But in this perhaps he rather follows others, 

 than adopted it after any examination of his own. That treatise never had the 

 finishing hand of its great author, and it is well known now in what manner it 

 came abroad. 



According to Riccioli, this eclipse was central at the Hellespont, and at Sardes 

 fell out at 6 in the afternoon ; and therefore is rejected by Mayer, in the Peters- 

 burg acts, as being too late in the day. 



According to my computation, the apparent time of the true conjunction was 

 at Greenwich, May 28, 4^35"' 15^; the beginning of the general eclipse 2*^3"' 

 30'; the end of the same 7^ l"" 46\ And by calculating the path of the pe- 

 numbra's centre over the earth's disk, it pretty plainly appears, that the centre of 

 the shadow passed so far from any place, where we can reasonably suppose the 



