HISTORY OF PHYSICAL ASTRONOMY.

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the moment, that the edge of the moon was formed of some dark,glutinous substance, which by its tenacity adhered to certain points ofthe sun’s limb, and by the motion of the moon was thus drawn out intolong threads, which suddenly broke and wholly disappeared*.

Mr. Baily remarks that the scene so riveted his attention, that he couldnot take his eye away from the telescope to note down anything duringthe progress of the phenomenon. He estimated, however, that the wholetook up six or eight seconds or ten at the utmost. The same phenomenonoccurred in a reverse order at the dissolution of the annulus. While thelimb of the moon was yet at some distance from the edge of the sun, anumber of long, black, thick, parallel lines suddenly darted forward fromthe moon, and joined the two limbs as before. As these dark lines gotshorter, the intervening bright parts assumed a more circular and irregularshape, and at length terminated in a fine curve line of bright beads, as atthe commencement, till they ultimately vanished, and the annulus ceasedto exist.

Mr. Baily also states that, although the parallel dark lines ought not tohave exhibited any perceptible difference of length, the outer lines imme-diately before their rupture seemed to he nearly double the length ofthose in the middle. This circumstance manifestly indicated a pro-tuberance on the moon’s limb at the point where it had just entered uponthe sun’s disk. A similar phenomenon had been noticed on the occasionsof the transit of Venus across the sun’s disk in the last century.

The phenomenon of which Mr. Baily gave so vivid a descriptionexcited great interest among astronomers, and future opportunities ofverifying it were anxiously looked forward to. The annular eclipse ofFeb. 18, 1838, which was visible in the United States of North America ,was peculiarly favourable for this purpose. On this occasion, however,the phenomenon was only partially observed. In several instances, theheads witnessed during previous annular eclipses at the instants of theformation and rupture of the annulus, were plainly visible, but no trace ofthe long black threads alluded to by Mr. Baily could be discerned by anyobserver. Moreover, it was found that even the heads were not per-ceptible in every case, their visibility seeming to be dependent on thecolour of the screen glass employed in observing the sun. With a redglass the phenomenon was generally perceived; but, when a green glasswas used, only a faint trace of it could be obtained, and in many cases itwas altogether invisible. Thus Prof. Henry, who observed the eclipseat Princeton College, New Jersey , with a 3| feet achromatic telescope,and a red screen glass, states that “ an appearance similar to a row ofbeads was regarded as the formation of the ring.” He adds that thedrops endured only for a second or twoj. On the other hand, Mr. R. T.Paine, who observed the eclipse at Washington with a telescope having agreen glass applied to it, was unable to discern the slightest vestige of thephenomenon. “The ring,” he remarks, “formed instantaneously, andbroke nearly so. No beads were seen, nor the dark lines mentioned byMr. Baily, nor the light round the moon, although all were looked for.No distortion of the moon’s limb could be seen, and the cusps of the sun,before the ring formed, were as sharp as needles.”];

It was expected that the observations of the total eclipse of July 8,

* Mem. Ast. Soc., vol. x., p. 7.

I Silliman’s Journ., vol. xxxviii., p. 167. f Ibid., vol. xxxviii., p. 164.