which will happen on Septemler 7, 1 820. 97 



greater accuracv, he should also make a diagram of the appear- 

 ance of the sun and moon, at the timeof the middle of the eclipse; 

 placing a mark against that part of the sun's disc which appears 

 the most vertical to him. The point on the circumference of the 

 Sim's disc (relative to its vertical or horizontal diameter) wiiere 

 the moon leaves it in order to form the annulus, and again where 

 it touches it at the timeof the dissolution of the annulus, should 

 also, if possible, be distinctly noted. M. Le Monnier considers 

 this of considerable importance*. 



It was observed, in the annular eclipse of 1737? that the an- 

 luilus was formed and dissolved verv suddenly. For when the 

 whole body of the moon had entered on the disc of the sun, the 

 last portion that entered appeared to adhere to the concave cir- 

 cumference of the sun's disc for some seconds ; and the moon 

 appeared elongated on that side, till the sun's light suddenly 

 broke round it, when the moon reassumed its regular curvature. 

 In a similar manner, when the disc of the moon approached the 

 concave line of the sun's disc on the other side, they seemed to 

 run together like two contiguous drops of water on a table, when 

 they touch each other. 



It was also observed, in the eclipse of 1737j " that, as the an- 

 nulus was forming, the light appeared to break in several irre- 

 gular spots near the point of contact: and that the limb of the 

 moon seemed to be indented there." These irregular parts 

 seemed likewise to have a kind of motion ; although there was 

 no undulation at the same time in the circumference of the sun. 

 Such appearances of a tremulous motion, in certain periods of 

 solar eclipses, are mentioned by Hevelius and others. It was 

 noticed also in the eclipse of 1748 f. 



In both these eclipses as well as in that of 1764 it was olj- 

 served that, when the annulus was formed, the moon appeared 

 much smaller on the sun than it really ought to be : and indeed 

 much smaller than the calculations seemed to warrant. But 



• In his paper Sitr I'utllif.i den iclip.ies fie soldi (wherein he has drawn 

 many impoitaiit consetiuences from the eclipse of 174B) he remiulis, re- 

 specting the method of determining the limits of the umbra, that " la plii- 

 part des ohservateurs, en pareil cas, suivent les routes ordinaires, et n'ont 

 jamais fait assez d'attention an point de la circonference du limbc dii soleil 

 ■oil se forment les ruptures de Fanneau : desormais ces points de la circonft-- 

 rence du disciue du soleil seront les plus importans, et nous fourniront les 

 limites que nous voudrons bien assigner." — Mem. de I 'Acad. (A'.v Sriciicen for 

 17(>5, page 4G.}. 



t The Rev. Mr. Irwin, who noticed the eclipse of 1 748 at Elgin, says that 

 " the formation and breaking of the annulus were sensibly to be observed, 

 and passed In a momeut; aH'ordiuf/ a very pleasing sight by the irregular 

 treniidons spots of tlu' sun." — Phil. Trans, vol. xlv. page 5!J5. 



Vol.n.l.No. 202. /'V'/'. 1820. G uheiher 



