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these returns the earth was not in a position to admit of its being seen. Toward the end of 1845 it again appeared and was observed in November and December. In January, 1846, as it came nearer to the earth and sun, it was found to have separated into two distinct bodies. At first the smaller of these was quite faint, but it seemed to increase in brightness until it became equal to the other.

The next return was in 1852. The two bodies were then found to be far more widely separated than before. In 1846 their distance apart was about two hundred thousand miles; in 1852 more than a million miles. The last observations were made in September, 1852. Although since that time the comet should have completed seven revolutions, it has never again been seen. From the former returns it was possible to compute the position where it should appear with a good deal of precision, and from its non-appearance we conclude that it has been completely disintegrated. We shall, in the next chapter, learn a little more about the matter which composed it.

Two or three comets have disappeared in the same way. They were observed for one or more revolutions, growing fainter and more attenuated on each occasion, and finally became completely invisible.

Of the periodic comets the one that is most frequently and regularly observed bears the name of Encke, the German astronomer who first accurately determined its motion. Its first discovery was made in 1786, but, as was often the case then, its orbit could not at first be