In 1843 another comet came up from the south, and presently returned thither.  It was, indeed, only seen during its return, having, like the comet of 1668, been only discovered a day or two after perihelion passage.  Astronomers soon began to notice a curious resemblance between the orbits of the two comets.  Remembering the comparative roughness of the observations made in 1668, it may be said that the two comets moved in the same orbit, so far as could be judged from observation.  The comet of 1843 came along a path inclined at apparently the same angle to the earth’s orbit plane, crossed that plane ascendingly at appreciably the same point, swept round in about two hours and a half that part of its angular circuit which lay north of the earth’s orbit plane, and, crossing that plane descendingly at the same point as the comet of 1668, passed along appreciably the same course toward the southern stellar regions!  The close resemblance of two paths, each so strikingly remarkable in itself, could not well be regarded as a mere accidental coincidence.

[Illustration:  The Constellations, though unnamed, can readily be identified, when it is noted that the Comet’s course, as here represented, began in the constellation of the Crane.]

However, at that time no very special attention was directed to the resemblance between the paths of the comets of 1843 and 1668.  It was not regarded as anything very new or striking that a comet should return after making a wide excursion round the sun; and those who noticed that the two comets really had traversed appreciably the same path around the immediate neighborhood of the sun, simply concluded that the comet of 1668 had come back in 1843, after 175 years, and not necessarily for the first time.

It must be noticed, however, before leaving this part of the record, that the comet of 1843 was suspected of behaving in a rather strange way when near the sun.  For the first observation, made rather roughly, indeed, with a sextant, by a man who had no idea of the interest his observation might afterward have, could not be reconciled by mathematicians (including the well-known mathematician, Benjamin Pierce) with the movement of the comet as subsequently observed.  It seemed as though when in the sun’s neighborhood the comet had undergone some disturbance, possibly internal, which had in slight degree affected its subsequent career.

According to some calculations, the comet of 1843 seemed to have a period of about thirty-five years, which accorded well with the idea that it was the comet of 1668, returned after five circuits.  Nor was it deemed at all surprising that the comet, conspicuous though it is, had not been detected in 1713, 1748, 1783, and 1818, for its path would carry it where it would be very apt to escape notice except in the southern hemisphere, and even there it might quite readily be missed.  The appearance of the comet of 1668 corresponded well with that of the comet of