was one of the most remarkable in the nineteenth century. It was discovered on the 2d of June, by Donati, of Florence, and first became visible to the naked eye about the last of August. The comet attained its greatest brilliancy about the 10th of October, when its distance from the earth was 50,000,000 miles. The length of its tail somewhat exceeded this distance. If, therefore, the comet had been at that time directly between the sun and the earth, the latter must have been enveloped for a number of hours in the cometic matter.
The observations of this comet during a period of five months enabled astronomers to determine the elements of its orbit within small limits of error. It completes a revolution, according to Newcomb, in 1854 years, in an orbit somewhat more eccentric than that of Halley's comet. It will not return before the 38th century, and will only reach its aphelion about the year 2800. Its motion per second when nearest the sun is 36 miles; when most remote, only 234 yards.
It remains to describe some of the most remarkable comets of which we have any record, but of which we have no means of determining with certainty whether they move in ellipses, parabolas, or hyperbolas.
In the year 466 B.C., a large comet appeared simultaneously with the famous fall of meteoric stones near Ægospotamos. The former was supposed by the ancients to have had some agency in producing the latter phenomenon. Another of extraordinary magnitude appeared in the year 373 B.C. This comet was so bright as to throw shadows, and its tail extended one-third of the distance from the horizon to the zenith. The years 156, 136, 130, and 48, before our era, were also signalized by the appearance of very large comets. The apparent magnitude of the first of these is said to have equaled that of the sun itself; while its light was sufficient to diminish sensibly the darkness of the night. The second is said to have filled a fourth part of the celestial hemisphere. The comet of 130 B.C., sometimes called the comet of Mithridates, because of its appearance about the time of his birth, is said to have rivaled the sun in splendor.
In A.D. 178 a large comet was visible during a period of nearly three months. Its nucleus had a remarkably red or fiery appearance, and the greatest length of its tail exceeded 60°. The most brilliant comets of the sixth century were probably those of 531 and 582. The train of the latter, as seen in the west soon after sunset, presented the appearance of a distant conflagration.