304 Obsei-vations on the 



of the moon's body, exceeded 7", the apex of the shadow would 

 fall within the mean distance of the node, and consequently a 

 solar eclipse could never happen. The nature of these lumi- 

 nous rings, therefore, seems altogether inexplicable ; at least, 

 the theories which have hitherto been proposed on that subject, 

 leave the question of a lunar atmosphere undecided. 



The evolution of greater light and heat from particular por- 

 tions of the unobscuredpart of the sun's disc, is one of the most 

 interesting phenomena connected with the subject of eclipses, 

 and at the same time appears one of the most inexplicable. 

 Dr. Halley is the first, and indeed the only observer, who dis- 

 tinctly noted the circumstance, and seems to have remarked it, 

 about the time of greatest obscuration only. On the present 

 occasion, however, from the obscuration of 5^ or 6 digits, to 

 the same phase in the egress, it was frequently experienced 

 that more light and heat were transmitted from the western than 

 from the eastern divisions of the sun's disc. This effect was 

 very sensibly felt on the eye and face, when the telescope was 

 pointed in immediate succession, to the respective portions of 

 the unobscured segment, taking care to move it across the 

 moon's dark surface, or below the sun's lower limb ; and to 

 admit into the field, only a small part of the enlightened disc 

 near each cusp. Dr. Halley's statement is somewhat different. 

 " When the first part of the sun remained on his east side, it 

 grew very faint, and was easily supportable to the naked eye 

 even through the telescope, for above a minute of time before 

 the total darkness; whereas, on the contrary, the eye could not 

 endure the splendour of the emerging beams through the teles- 

 cope even for a moment. He ascribes this to two causes, " the 

 dilatation of the pupil during the darkness, which before 

 had been contracted by looking on the sun," and the eastern 

 parts of the lunar atmosphere being replete with vapours raised 

 from a surface exposed during thirty days to the rays of 

 the sun, and from the opposite cause the western parts would 

 be pure and transparent. Neither of these seems a satis- 

 factory explanation; the fact indeed scarce admits of one, but 



