Page:The story of the comets.djvu/102

66 The Rev. H. C. Key, speaking in the first instance of what he saw on December 3. said :—

The return of 1871 was also important because it was found not to have been accelerated in accordance with the Resisting Medium theory as previous returns had been, since the first discovery of the comet in 1786. Von Asten's conjecture as to this is that in 1869 the comet might have come into collision with some minor planet which violently deranged and modified its orbit in some degree.

Passing over the returns of 1875 and 1878 we come to that of 1881, in which year the comet passed through perihelion on Nov. 18. Common, using a 3-ft. reflector, noted the comet to be about 2' in diameter, very faint even in an instrument of that size, and with slight indications of an increased brightness in the centre. Tacchini found the spectrum exhibiting bright bands in the yellow, green, and blue respectively, coinciding with the 3 principal bands seen in the spectra of the hydro-carbons. As in the case of some other comets, the bands were shaded off to the blue. A faint continuous spectrum was also detected. The spectrum was considered to have undergone no change since the previous examination in 1878.

Since 1881 Encke's Comet has returned and been observed