SCIENTIFIC SUMMARY. 
107 • 
9.30 p.m., the fantail was still faintly visible, but the bright jet of light 
was now turned in the contrary direction to the tail and appeared like a 
miniature comet. The aspect of the comet had considerably changed 
since the preceding evening, and the tail appeared to have become broader 
and brighter, and to be connected with the head in a more solid manner. 
No opportunity occurred of viewing the comet before August 31, when a 
great change was observed to have taken place. The head and tail were 
now similar in appearance to those of Donati’s and the great comet of 1861 
— the fantail was brighter than on former occasions : the edges being the 
most brilliant portions ; and the tail was now almost as broad as the head, 
although considerably fainter. Instead of the appearance of a bulbous 
root attached to a slight stem, it had assumed the ordinary shape of large 
comets. It will be seen from the foregoing observations and accompanying 
plate that the position of the fantail, but more particularly that of the 
luminous jet within it, was constantly varying. The same phenomenon has 
been noticed in every great comet observed since the invention of the telescope, 
although it is only of late years that the matter has been thoroughly investi- 
gated. Bessel considered that it was a real oscillation to and fro, dependent 
on the action of the sun. The observations made by M. Chacornac on the 
present comet seem, however, to show that no oscillation takes place, and 
that the jets of light are separate and distinct. Having narrowly watched 
the different phases (on one occasion for upwards of sixteen hours without 
interruption), he comes to the conclusion that, as the comet approaches 
near the sun, the nucleus emits a vaporoirs jet (something like that of 
steam) in the direction of the central luminary. This preserves a recti- 
linear form for some time, showing that considerable force is exerted at 
the time; but this latter subsequently becomes comparatively weakened, 
and the jet takes the form of a cornucopia. It finally becomes foggy 
and diffused, and the active emission appears to have altogether ceased, 
when another ray and fresh jet make their appearance about thirty 
degrees from the first, which, passing through all the changes previously 
undergone by that, finally vanishes away in the lapse of about sixteen 
hours, whilst the original jet again comes into view. It remains to be 
seen whether this curious discovery will be verified by the whole series of 
observations ; at all events, it will put observers on the watch to folloAV 
more narrowly the changes occurring in those (in every respect) erratic 
and mysterious objects. It may be added that the path described by this 
comet bears no resemblance to any previously observed. It passed at its 
shortest distance from the sun on August 23, when its distance from that 
luminary was about ninety-two millions of miles. It moved in an orbit 
inclined sixty-six degrees to the ecliptic, and the head, it was reckoned, 
was about 100,000 miles in diameter. 
Two well-certified disappearances of nebulas have been recorded within 
the last three months. In both cases the original observations have been 
of recent date, so that there can be no suspicion of mistake. The first is 
situate at 3h. 21m. of R.A., and -j- 30° 54' of Decl. A few years since it 
was visible in a two-foot comet-seeker. In 1859, February, it was barely 
visible in a telescope of three-inch aperture ; and, in August of the pre- 
sent year, it was scarcely perceptible in the great Copenhagen refractor. 
