Josephus tells us that the destruction of Jerusalem in 69 A.D. was caused by no less than the sword shaped comet which pierced the heavens above the city!
A story is sometimes told of the great consternation caused in Europe in 1456 at the appearance of Halley's comet. This great shaft of light moving across the sky so disturbed the equanimity of Pope Calixtus that he instituted a form of prayer ("Lord, deliver us from the devil, the Turk and the comet") as a protection against its baleful influence. But the comet remained, and, with his people mightily afraid, the pope himself was forced "to interfere, exorcise and expell" the malignant one from the skies.
Halley's comet has always been a most interesting comet. The last time that it appeared, in 1910, the earth rolled right through its beautiful, highly diffused tail, and although the experience was of interest to astronomers, it affected not a whit the affairs of the populace; indeed, but few people knew about it.
In 1680, Halley, an English astronomer and mathematician, while on a passage to France, was the first to observe this great comet, and later made observations with Cassini at Paris, where he observed its appearance with great care and painstakingly computed the elements of its orbit. From the nature of its orbit, he predicted that it would return at regular intervals of 75 years. He even traced this comet back on his historical table of comets, and found that the comets of 1607, 1531 and 1456 had the same orbit as the one which had appeared in 1680. Seventy-five years after, true to his prediction, the comet returned, thus proving that comets may travel in elongated orbits and appear periodically. Halley has the honor of being the first to predict the return of a comet.
It is now known that some comets require hundreds and even thousands of years to perform a revolution around the sun; Donati's comet, one of the most famous comets, which appeared
[236]
