We now proceed to describe The Halo, or Corona; and similar Appearances. - An Halo is a luminous circle surrounding the sun, moon, planets, or fixed stars. Occasionally these circles are white, and sometimes they are coloured like the rainbow. Sometimes one only is visible, and at others several concentric halos appear at the same time. Mr. Huygens observed red next the sun, and a pale blue outwards. Sometimes they are red on the inside, and white on the outside. In France, one was observed in 1683, the middle of which was white; after which followed a border of red, next to it was blue, then green, and the outermost circle was a bright red. In 172b, one was seen of a pale red outwardly, then followed yellow, and then green, terminated by a white. In Holland, M. Mus-chenbroek says, fifty may be seen in the day-time, almost every year; but they are difficult to be observed, except the eye be so situated, that not the body of the sun, but only the neighbouring parts of the heavens, can be seen. Mr. Mid-dleton says, that this phenomenon is very frequent in North America; for that there is generally one or two about the sun every week, and as many about the moon every month. Halos round the sun are very frequent in Russia. M. AEpinus says, that from the 23d of April, 1758, to the 20th of September, he himself had observed no less than twenty-six, and that he has sometimes seen twice as many in the same space of time.

Similar, in some espects, to the halo, was the remarkable appearance which M. Bouguer describes, as observed on the top of Mount Pichinca, in the Cordilleras. When the sun was just rising behind them, so as to appear white, each of hem saw his own shadow projected upon it, and no other. The distance was such, that all the parts of the shadow were easily distinguishable, as the arms, the legs, and the head; but what surprised them most was, that the head was adorned with a kind of glory, consisting of three or four small concentric crowns, of a very lively colour, each exhibiting all the varieties of the primary rainbow, and having the circle of red on the outside. The intervals between these circles continued equal, though the diameters of them all were constantly changing. The last of them was very faint; and at a considerable distance was another great white circle, which surounded the whole. This phenomenon never appeared but in a cloud consisting of frozen particles, and never in drops of rain like the rainbow. When the sun was not in the horizon, only part of the white circle was visible, as M. Bouquer frequently observed afterwards. Similar to this curious appearance, was one seen by Dr. M'Fait in Scotland; who observed a rainbov; round his shadow in the mist, when he was upon an eminence above it. In this situation the whole country round seemed buried under a vast deluge, and nothing but the tops of distant hills appeared here and there above the flood. In those upper regions, the air, he says, is at that time very pure and agreeable. At another time he observed a double range of colours round his shadow. The colours of the outermost range were broad and very distinct, and every where about two feet distant from the shadow. Then there was a darkish interval, and after that another narrower range of colours, closely surrounding the shadow, which was very much contracted. He thinks that these ranges of colours are caused by the inflection of the rays of light, the same that occasions the ring of light which surrounds the shadow of all bodies, observed by M. Maraldi, and others.