98 Memoir relative to the Annular Eclipse of the Sun, 



whether this phaenomenon arises from an apparent enlargement 

 of the sun's disc, or from an apparent diminution of the moon's 

 disc, or from both, does not seem clearly decided. M. Du Se- 

 jour has discussed this subject, with his usual ability, in his Traite 

 analytique dcs mouvemens apparens des corps celestes, vol. i. 

 page 'JOo, &c.: but he has not come to any precise determina- 

 tion thereon. The observations have not been made with suffi- 

 cient accuracy, nor are they sufficiently numerous to enable us 

 to determine so nice an element in the calculation of eclipses. 

 It is hoped therefore that the attention of astronomers will be 

 more drawn towards this subject in the ensuing eclipse*. 



In tlie eclipse of 1737, Maclaurin observes that about 20 seconds 

 " before the annuliis was complete, a remarkable point or speck 

 of pale light appeared near the middle of the part of the moon's 

 circumference that was not yet come upon the disc of the sun : 

 and a gleam of light, more faint than that point, seemed to ex- 

 tend from it to each horn." 



In the eclipse of 17^8, it was noticed that there was, " about 

 the middle of tiie eclipse, a remarkal)]y large spot of light, of an 

 irregular figure and of a considerable brightness, about T or 8' 

 within the limb of the moon." Mr. Short states that this eclipse 

 was not quite annular at Aberdour Castle: the cusps seemed to 

 want about one-seventh of the moon's circumference to be joined, 

 yet a brown light was plainly observed both by my Lord Morton 

 and myself to proceed or stretch along the circumference of the 

 moon, from each of the cusps, about one-third of the whole di- 

 stance of the cusps from each cusp; and there remained about 

 one-third of the whole distance of the cusps not. enlightened by 

 this brown light." — " I observed at the extremity of this brown 

 light, which came from the western cusp, a larger quantity of 

 light than in any other place, which at first surprised me ; but 

 afterwards I imagined it must have proceeded from some cavity 

 or valley made by two adjoining mountains on the edge or limb 

 of the moon. I had often formerly observed mountains on the 

 circumference of the moon, more or less every where round it, 

 but never saw them so plain as during the time of this eclipse. 

 The mountainous inequalities on the southern limb of the moon 

 were particularly remarkable ; in some parts mountains and val- 

 leys alternately; others extended a considerable way along the 



* See Lalande's Aitfronomie, vol. ii. page 445 ; Delambre's Astronomh, 

 vol. ii. page 423; and also M. Le Monnier's memoir Sur les eclipses totales 

 du soldi, in the Mcni. dc I'Acad. des Sciences for 1781, page 243. In this 

 memoir there is a map of the path of the moon's umbra in the total eclipse 

 of May § J, 1 724, and wliich appears to have proceeded over great part of 

 England : nevertheless I cannot find any observation of it in this country. 



circum- 



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