By October 3 a marvelous change had taken place in the appearance of the comet. The train had increased in length and brightness, extending nearly as far as Eta in Ursa Major, and the straight ray or secondary train was still very much in evidence. It was supplemented by another slender ray, as shown in drawings made by Professor Bond on October 4 and 5, but it had vanished by October 6, although its position was indicated, for that date, in the faint suggestion of a ray between the main tail and the outer or secondary tail. The bright star to the left of the nucleus of the comet is Arcturus (in the constellation Boötes), over which the comet passed without perceptibly diminishing its brightness, thus showing of what airy texture the train of a comet is composed. Was it not Sir John Herschel who said that a comet could be easily packed in a portmanteau, and in the recent edition of _The Vault of Heaven_ Sir Richard Gregory gives the following unique illustration of the insignificance of the whole mass of a comet: [Illustration: COMET OF DONATI Photograph taken October 10, 1858, at Harvard College Observatory ] “Suppose we could take a comet, head, tail and all, and put it in one pan of a balance, and we could carve out from the air which surrounds us an object of the same size to put in the other pan, we should find that our aërial body weighed four or five thousand times more than the comet. But though a comet as a whole is lighter than air, it must not be concluded that comets consist solely of gases in a state of extreme tenuity. The head may be, and very probably is, composed of a large number of small but solid bodies; nevertheless, when a comet is taken in its entirety, the mean density is extremely low.” By October 10, the comet was receding from the neighborhood of Ursa Major, drifting across the constellation of Boötes. On this date the comet made its nearest approach to the earth. Its train now resembled that of a widely opened fan, but its outline was already growing dim. It showed strange alterations of dark and bright bands, resembling the streamers which are sometimes seen to break up the continuous outline of an auroral arch. The extreme length of the tail was nearly 64°, the greatest extent observed during the apparition of the comet. The secondary tail was still visible, but extremely faint.