﻿Observations of Comets. 457 



nuous spectrum, and was probably solar light sent to us by ordi- 

 nary reflection. 



Previous telescopic observations bad shown that in several 

 bright comets the light of the head differed from solar light in 

 having a decided blue tint*. In this part of the comet the po- 

 lariscope has generally given but feeble indications of the pre- 

 sence of reflected light. These characters are in accordance 

 with the spectroscopic examination of the light of this part of 

 comets. 



I will now describe the more complete analysis of the blue 

 cometary light which the brighter comets of last summer enabled 

 me to make. 



One of these was Brorsen's comet at its return in 1868, the 

 other a comet discovered by Winnecke-j\ 



Winnecke's comet (Comet II. 1868) presented in the telescope 

 a nearly circular coma surrounding a bright nebulous spot, where 

 probably a true nucleus existed. The faint nebulosity from the 

 margin of the coma could be traced for more than a degree, and 

 formed a tail which was sharply defined on the following edge, 

 but faded away so gradually on the opposite side that no limit 

 could be perceived. In the spectroscopic observations the slit 

 was placed across a diameter of the head. 



The spectrum of this comet, and also that of Brorsen's comet, 

 consisted of three bright bands in similar but not identical parts 

 of the spectrum. The circumstance that the bands were nar- 

 rower than those of the other comet might be due to the smaller 

 intensity of the light of this comet, in consequence of which the 

 bands could not be traced so far in the instrument. If this pos- 

 sible explanation of the difference in breadth of the bands be 

 admitted, there will remain the difference of refrangibility in 

 the strongly marked beginning of the middle bands of the two 



* Sir William Herschel described the head of the comet of 1811 to be 

 of a greenish or bluish- green colour, while the central point appeared to be 

 of a pale ruddy tint. The representations of Halley's comet at its appear- 

 ance in 1835 by the elder Struve are coloured bluish green, and the nucleus 

 on October 9 is coloured reddish yellow. He describes the nucleus on that 

 day thus : — " Der Kern zeigte sich wie eine kleine, etwas ins gelbliche 

 spielende, gliihende Kohle von l'anglicher Form" {Beobachtungen des Hal- 

 ley' schen Cometen, p. 41). Dr. Wmnecke describes similar colours in the 

 bright comet of 1862 : — " Die Farbe des Strahls erscheintmir gelbrothlich, 



die des umgebenden Nebels (vielleicht aus Contrast.) mattblaulich 



Die Farbe der Ausstromung erscheint mir gelblich ; die Coma hat blau- 

 liches Licht" {Memoir es de V Academic Imperiale des Sciences de St.Peters- 

 bourg, vol. vii. No. 7)- 



t For a more detailed account of the observations of these comets and 

 diagrams of their spectra, the reader is referred to papers by the lecturer in 

 the Proceedings of the Royal Society, vol. xvi. p. 386 ; and Phil. Trans. 

 1868, p. 555. 



