Page:The story of the comets.djvu/106

70 epoch of the next perihelion passage was fixed for Sept. 26, 1851, but the comet's position then was not favourable owing to its proximity to the Sun, and it escaped observation. Bruhns re-discovered it on March 18, 1857. I remember to have seen it on March 23. It possessed the usual nebulous appearance of telescopic comets generally, and appeared to have a diameter of about 2'. though its position in the morning twilight probably marred its brilliancy. This comet again returned to perihelion in Oct. 1862 (not seen), in April 1868, in Oct. 1873, and in March 1879. The spectroscopic observations on the last-named occasion by Konkoly in Hungary and C. A. Young in America tended to show that the spectra of this comet and of Encke's Comet were identical with one another, and with a hydro-carbon spectrum. This comet escaped notice at its return in Sept. 1884, and was missed again in 1890, although favourably placed and sought for by powerful instruments. It was due to return to perihelion again in Aug. 1895 but was missed, and was again missed in 1900-1 and in 1906, so that it is not very clear whether we are entitled to recognize it as a permanent member of the Solar system. [See Fig. 36, Plate X.]

The period of Brorsen's Comet has been gradually diminishing owing to the effect of planetary perturbation. Thus:—

and this diminution appears to have been going on ever since 1879.

The period being now 5⋅5 years, more or less, it results that the comet is alternately visible in spring and autumn, and the former apparitions are specially favourable for observations, because at this season, in consequence of the great inclination of the orbit, the comet reaches a high