L. Trouvelot—Sudden extinction of the Light, etc. 85 
y Ursee Majoris 
Be it coincidence-or not, at the moment that this phenomenon 
was occurring, a strong magnetic perturbation was going on in 
Cambridge, where the declination needle oscillated through an 
angle of 1° 27’, although no auroral light was seen; and by 
the kindness of Mr. Cleveland Abbe, of the Signal Corps, I 
learn that no aurora was reported for that night. 
It is not a new thing to see vibrations and pulsations ran- 
ning along the tail of comets. Many observers have seen this 
eeepothen hs among others Longomontanus, Vandelin, Snel- 
ius and Father Cysat, who are reported to have seen undula- 
tions taking place on the border of the Comet of 1618, as if it 
was agitated by the wind. Hevelius observed analogous mo- 
tions in the Comets of 1652 and 1661. Pingré asserted that he 
distinctly saw in the long tail of the Comet of 1769, “des 
ondulations semblables a celles que les aurores boréales pré- 
sentent.”* According to Winnecke, from the 5th to the 12th 
of October, 1858, the rays forming the superior part of Donati’s 
comet spread and contracted suddenly like the rays of the 
aurora, 
Cambridge, Jan. 5, 1877. 
Art. XI.— Sudden extinction of the light of a Solar Protuberauce ; 
by L. TROUVELOT. 
_ ON the 26th of June, 1874, while making my daily observa- 
tions of the sun with the spectroscope at the Harvard College 
Observatory, Il saw an unusual phenomenon, which may be 
worth recording. The narrow slit of the instrument was di- 
rected on the preceding side, about 270°, just above a group of 
Spots which was then very near the limb, when I saw a ril- 
hant protuberance partly projected on the spectrum, on the side 
of the rays of less refrangi bility. In shape, this hydrogen flame 
resembled an elongated comma, having its acute extremity 
directed toward the sun, where it terminated just a little above 
the chromosphere. The chromosphere under this protuberance 
formed several slender and acute aigrette-shaped flames, none 
of which, however, reached it. The large prominence, which 
was slightly inclined to the limb, had a height of 3’ 37”, and 
about 3° in its greatest width. 
* Arago, Astro. pop., vol. ii, p. 439, Paris, 1855. 
