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Some German journalists predicted that it would cross the earth's orbit near the point at which the earth would be at the time, and cause the destruction of our globe. Such was the

degree of alarm excited on this occasion, that M. G***, a professor in Paris, put the question to the Academy of Sciences, whether it did not consider itself bound in duty to refute, as speedily as possible, this assertion. "Popular tertors," he observed, "are productive of serious consequences. Several members of the Academy may still remember the accidents and disorders which followed a similar threat, imprudently communicated to the Academy by M. de Lalande, in May, 1773. Persons of weak minds died of fright, and women miscarried. There were not wanting people who knew too well the art of turning to their advantage the alarm inspired by the approaching comet, and places in paradise were sold at a very high rate. The announcement of the comet of 1832 may produce similar effects, unless the authority of the Academy apply a prompt remedy; and this salutary interven→ tion is at this moment implored by many benevolent persons." It was supposed by some, that if any disturbing cause should delay the arrival of the comet for some months, the earth must pass directly through its head.

In order to dispel such fears, and to illustrate the nature of these bodies, M. Arago published an excellent and popular treatise on comets in the "Annuaire" of 1832. He showed that the result of the calculation was, that the passage of the comet ought to proceed a little within our orbit, and at a distance from that curve, which is equal to four terrestrial radii and two thirds, or about 37,000 miles; that on the 29th Oc tober, 1832, a portion of the earth's orbit might be included within the nebulosity of the comet; but that the earth would not arrive at the same point of its orbit till the morning of the 30th November, or more than a month afterward; and, consequently, that the earth would be more than twenty millions of French leagues (or fifty millions of British miles) distant from the comet. He adds, that "if the comet, instead of crossing the plane of the ecliptic on the 29th October, had not arrived there till the morning of the 30th November, it would have undoubtedly mingled its atmosphere with ours, and perhaps even have struck us!" The earth is considered in more danger, if danger there be, from this comet and that of Encke then from any other. Encke's comet crosses the orbit of the

earth sixty times in the course of a century, and there is certainly a possibility that it might come into collision with the earth, but the probability of its doing so is very small; and, besides, this comet and that of Gambart are so extremely rare, that little danger is to be apprehended, even although a contact were to take place. Gambart's is a small, insignificant comet, without a tail, or any appearance whatever of a solid nucleus, and is not distinguishable by the naked eye.

7. The comet of 1807. This was the first comet on which I had an opportunity of making observations. My first observation was on the evening of October the 8th, 1807, a little after sunset, when it appeared in a northwesterly direction, not far distant from Arcturus, which was then only a little above the horizon. To the naked eye it appeared somewhat like a dim nebulous star of the second magnitude, with a beam of light on one side of it. Through a telescope, its tail presented a pretty brilliant appearance, and occupied a space of consid. erable more than a degree in length. The coma seemed to have a roundish appearance, and appeared more indistinct as the magnifying power was increased. When viewed with an achromatic telescope of thirty-one inches focal distance, and a power of thirty, it presented a very distinct and beautiful appearance, and the nucleus, coma, and tail nearly filled the field of view. When a power of sixty was applied, it was much more indistinct than with the former power, and in all the subsequent observations the lower power was generally preferred. In the course of five or six weeks, or about the middle of November, it disappeared to the naked eye. I traced it with the telescope, as often as the weather would' permit, for two or three months after it had become invisible to the unassisted sight, and found that its apparent motion was pretty rapid, and towards the northeast. About the middle of January, 1808, at eleven P.M., it appeared in a direction northeast by north; and at this time it appeared through the telescope like a small nebulous star, or like those species of comets called bearded comets, having no trace of anything similar to a tail. The last time I saw it was about the end of January, when it was still distinctly visible, like a nebulous star; but cloudy weather for nearly a fortnight prevented any farther observations, and I saw it no more. On the evening in which I had the last peep of it, I detected another comet within eight or ten degrees of it, which appeared like a star of

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the third magnitude, and exhibited a pretty brilliant appearance through the telescope. It had no tail, like the former comet, but appeared surrounded with radiant hairs like the glory which painters represent around the head of our Saviour. It continued visible for several weeks; but I have not seen any particular notices of this second comet, or any special observations on it, which have been recorded by astronomers.

This comet appears to have been first noticed by Herschel and Schroeter about the 4th of October, 1807, who continued their observations upon it for several months. According to Schroeter's observations and estimates, the diameter of the nucleus of this comet was about 4600 miles, or nearly the size of the planet Mars, and appeared to be of considerable density; the diameter of its coma 120,000 miles, but liable, at different times, to variations of increase and decrease; and its rate of motion, at certain periods, 1,333,380 miles a day, or 55,557 miles an hour. Its tail was divided in a very unusual manner into two separate branches; the north side continued much brighter and better defined than the other, and was also invariably convex, while the other side was concave. But what was deemed most remarkable was the variation in length and the coruscations of the tail. Something like coruscation had been observed by the naked eye in the case of preceding comets, and such phenomena appear to have been confirmed by the observations of Schroeter. In less than one second, streamers shot forth to two and a half degrees in length; they as rapidly disappeared and issued out again, sometimes in portions, and interrupted like our northern lights. Afterward the tail varied both in length and breadth, and in some of the observations the streamers shot from the whole expanded end of the tail, sometimes here, sometimes there, in an instant, two and a half degrees long, so that within a single second they must have shot out a distance of 4,600,000 miles. Their light was also sometimes whiter and clearer at the end than at the base, as is occasionally seen in the northern lights. Some have objected to the extreme rapidity of the streamers as here stated, but the fact of coruscations having been seen appears to be confirmed by the observations of this celebrated and accurate observer. The observations of Herschel on this comet differ in some respects from those of Schroeter, particularly in the estimate he makes of the size of the nucleus, which he reckons to be considerably smaller than what has been stated above.

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