' HISTORY OF PHYSICAL ASTRONOMY.

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Powell in tlie analogous case of annular eclipses. The appearancenoticed by Mr. Dunn seems to be totally inexplicable, unless it beassimilated to the dark lines witnessed during the annular eclipse of1830, and other similar occurrences.

It was remarked by several observers of the transits of 1761 and 1760,that both at the ingress and egress, the portion of the limb of the planetthat was off the sun, was visible by means of a faint light surrounding itin the form of a ring. La Chappe, who observed the transit of 1761 atTobolsk, in Siberia , states that the light of the ring was of a very deepyellow near the body of the planet, but that it became more brillianttowards the outer border*. MM. Stromer, Mallet, Bergman, andMelander,who observed the same transit at Upsal, remarked that when three-fourthsof the planet’s limb had entered upon the sun, the remaining fourth wasvisible by means of a faint ring which appeared around itf. A similarphenomenon was observed on the same occasion by Wargeutin at Stock-liolm, by Planman at Ca,jainbourg , and in several other instances J.

Dr. Maskelyne, who observed the ingress of Venus upon the sun’s diskat Greenwich on the occasion of the transit of 1709, states that, when theplanet was little more than half entered upon the sun, he saw her wholecircumference completed, by means of a vivid but narrow and ill-definedborder of light, which illuminated that part of her circumference that wasoff the sun. He adds that it disappeared two or three minutes before theinternal contact §. A similar phenomenon was witnessed during the sametransit, by Wales and Dymond at Hudson’s Bay ||, by Pingre and DeFleurieu at Gape Francis in the Island of St. Domingo IT, and by variousother observers in different places.

Several of the observers of the transits of 1617 and 17G9 remarkedthat, when Venus was wholly entered upon the sun, there appeared a faintring around her limb. Dunn, in his account of the transit of 1769,describes it as a lucid annulus about five or six seconds in breadth, some-what dusky towards the limb of the planet, and at the outer margin tingeda little with blue**. Mr. Hitchins, alluding to the same phenomenon,states that it was excessively white and faint, and that it was brightesttowards the body of the planet ff. Nairne asserts that it appeared brighterand whiter than the body of the sun JJ;.

It is worthy of remark that, in general, those individuals who observed afaint light around the part of the limb of Venus that was off the sun, on theoccasion of the transits of 1761 and 1769, do not seem to have perceived thecomplete annulus around.the limb of the planet when it was wholly enteredupon the sun’s disk. On the other hand, most of those observers whowitnessed the latter phenomenon do not make any allusion to the formeras having been seen by them. The observations of La Chappe, Maskelyne,and several other individuals, are very clear upon this point. It wnuldseem, therefore, that the two phenomena are not of the same nature. Withrespect to the physical origin of either, no satisfactory explanation has yetbeen offered. The appearance noticed when the planet was only partiallyon the sun, has a strong analogy to that alluded to by M. Arago andseveral other persons in France relative to the visibility of the whole ofthe moon’s limb during the progress of the total eclipse of the sun of

* Mem. Acad, des Sciences, 1761, p. 363. + Ibid., p. 364. J Ibid.

§ Phil. Trans., 1768, p. 357. || Ibid., 1769, p. 482. f Ibid., 1770, p. 498.

** Ibid., 1770, p. 71. If Ibid., 1768, p. 363. ff Ibid., p. 364.