HISTOEY OF PHYSICAL ASTEONOMY.

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Halley’s account of the total eclipse of the sun which happened atLondon in 1715, corroborates the testimony of preceding observers withrespect to the existence of the luminous ring, and also contains some in-teresting particulars relative to its physical aspect. “ A few seconds,”says he, “ before the sun was all hid, there discovered itself round themoon a luminous ring about a digit, or perhaps a tenth part, of the moon’sdiameter in breadth. It was of a pale whiteness or rather pearl colour,seeming to me a little tinged with the colours of the Iris , and to be con-centric with the moon.” He remarked, moreover, that the ring appearedmuch whiter and more brilliant near the body of the moon than at a dis-tance from it, and that the exterf&r boundary was very ill defined, seem-ing to be determined only by the extreme rarity of the luminous matter *.

The account of the appearance of the ring on this occasion, given bythe French astronomer Louville, tends to confirm the truth of Halley’sremarks. lie has stated, however, that there were interruptions in itsbrightness, causing it to resemble the radial glory with which painters en-circle the heads of the saints. He asserted with confidence that it ap-peared to be concentric with the moon f.

The luminous ring formed a conspicuous feature of the total eclipse ofthe sun w'hich occurred on the 22nd of May, 1724. Maraldi has stated,that at the commencement of the total immersion, the ring appearedbroader on the east than on the west side; but, on the other hand, that atthe end of the total immersion, it appeared broader-on the west side. Heremarked also that the breadth of the ring where it bordered upon thenorthern limb of the moon, was greater than the breadth at the part bor-dering upon the southern limb J.

The luminous ring appeared with great splendour on the occasion of thetotal eclipse of 1733. A great many interesting observations relative toit, due chiefly to Lutheran pastors, are to be found in the fourth volume ofthe Transactions of the Royal Society of Sweden §. The following are a

* Phil. Trans., 1715, p. 249.

+ Mem. Acad, des Sciences, 1715, p. 90. t Ibid., 1724, p. 178.

§ Nothing can be more praiseworthy than the zeal with which the clergymen in therural districts of Sweden responded to the invitation of the Royal Society of that countryto note the various phenomena connected with the occurrence of the total eclipse of1733. The observations transmitted by them to the Society on this occasion, were allarranged methodically by Celsius, previous to their insertion in the volume referred toin the text. Although they cannot pretend to much precision, still it may be assertedwithout hesitation, that they form the most complete description of a total eclipse of thesun which is to be found in the records of astronomical observation previous to the totaleclipse of 1842. This is more especially remarkable, as only a few years previously,other two total eclipses of the sun had happened (in fact, during the intermediate periodthe moon’s node in the one ease had made only half a revolution, and in the other notmore than a whole revolution), by means of which the inhabitants of the two countries ofwestern Europe, which boast of their superior civilization, had an opportunity of makingsimilar observations. With respect to the total eclipse of 1715, the account given byHalley is the only one due to an English observer which contains a single remark of aphysical nature. The other descriptions, relating to the duration and magnitude of theeclipse, merely served the purpose of enabling Halley to determine the precise track ofthe lunar shadow as it passed over England. Something might have been expectedfrom Cotes, who observed the eclipse at Cambridge; but, according to Halley, he hadthe misfortune to be oppressed with too much company. The accounts given by theFrench observers of the total eclipse of 1724, are still more meagre and unsatisfactory;since in this case there is not even one description which might compensate, in somedegree by its merits, for the barrenness of the others.