It was computed by Olbers that if a comet having a mass of 1/2000th of the earth's mass--which would form a globe of about 520 miles in diameter and of the density of granite--collided with the earth, with a velocity of 40 miles a second, our globe would be shattered into fragments.[200] But that any comet has a solid nucleus of this size seems very doubtful; and we may further say that the collision of the earth with _any_ comet is highly improbable. It seems to be a common idea that harvests are affected by comets, and even "comet wines" are sometimes spoken of. But we know that the earth receives practically no heat from the brightest comet. Even in the case of the brilliant comet of 1811, one of the finest on record, it was found that "all the efforts to concentrate its rays did not produce the slightest effect on the blackened bulb of the most sensitive thermometer." Arago found that the year 1808, in which several comets were visible, was a cold year, "and 1831, in which there was no comet, enjoyed a much higher temperature than 1819, when there were three comets, one of which was very brilliant."[201] We may, therefore, safely conclude that even a large comet has no effect whatever on the weather. From calculations on the orbit of Halley's comet, the next return of which is due in 1910, Messrs. Cowell and Crommelin find that the identity of the comet shown on the Bayeux Tapestry with Halley's comet is now "fully established." They find that the date of perihelion passage was March 25, 1066, which differs by only 4 days from the date found by Hind. The imposing aspect of the comet in 1066 described in European chronicles of that time is confirmed by the Chinese Annals. In the latter records the brightness is compared to that of Venus, and even with that of the moon! The comparison with the moon was probably an exaggeration, but the comet doubtless made a very brilliant show. In the Bayeux Tapestry the inscription on the wall behind the spectators reads: "_isti mirant stella_." Now, this is bad Latin, and Mr. W. T. Lynn has made the interesting suggestion that some of the letters are hidden by the buildings in front and that the real sentence is "_isti mirantur stellam_."[202] The present writer has examined the copy of the Bayeux Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn's suggestion seems very plausible. But the last letter of _stellam_ is apparently hidden by the comet's tail, which does not seem very probable!