Solar EcHpse. 30 1 



Among the phenomena, which have been considered as most 

 directly indicating the presence of this atmosphere, are to be 

 reckoned those luminous circles or halos, which, at the time of 

 complete immersion, in total and annular eclipses have been 

 observed concentric with, and immediately surrounding the 

 moon's circumference. No appearance of this nature could be 

 observed on the present occasion ; about 2' indeed after the 

 conjunction, as determined by previous calculation, the dark 

 and hitherto strongly defined outline of the periphery seemed 

 less distinct, but without the slightest appearance of any ex- 

 traneous matter. 



From the original observations, it appears, that these lumi- 

 nous rings seemed to break out from behind the moon, varying 

 in breadth from a digit to -jJ^ of a diameter. They were brightest 

 near the body of the moon, and of a pale, or, as it is expressed, 

 " pearly" light, gradually diminishing in splendour as the dis- 

 tance increased, and apparently " terminated by the extreme 

 rarity of the matter of which they were composed*," 



In order to account for these appearances, three different 

 theories have been proposed. The hypothesis of Cassini, in 

 which it was assumed that they proceed from the effects not of 

 a lunar, but of a solar, atmosphere, appears never to have been 

 generally adopted. The principles of the other two are thus 

 briefly stated by Le Monnier. " Ou bien la lune est envi- 

 ronnee d'une atmosphere tres deliee, et dont la matiere est fort 



* Phil. Trans. Mem. det VAcad. des Sciences. Mem. de Berlin, (Euler). 

 Mem. de V Institut. (LalandeJ. There is a remarkable coincidence in the 

 estimates of the breadth of these circular areas. Flanistead, Halley, 

 Cassini, ^c, stating it as in the text, and others even greater. M. de 

 Ihering'smeasurement it is not now easy exactly to ascertain. *' Un filet de 

 luminicre sciubloit masquer le disc de la lune, et qui s' etendoit a une dis- 

 tance de cornesegal a pen pres a I'espace compris entre trois fils de micro- 

 metre." {Mem. de V Acad, den Sciences, mi. 1748, p. 56.) The colour of 

 these rings does not appear to have been invariably a pale white, but in 

 some instances extremely brilliant: thus Cassini mentions, that at Zurich, 

 " Le sollci fut convert pendant ((uatre minutes, et le bord de la lune parois- 

 soil coninic un anncuii d'lir. Mem, de /' Acad, &C., ««. 1706, p. 347. 



