1871]. Mr. W. Hug-gins on the Spectrum of Encke's Comet. 45 



of water and filtered into two flasks. When cold, one of these was put 

 out at 8.35. At 10.30 the temperature was 35°, and next morning at 

 8 a.m. 31°. The flask was now brought in and left on the mantle-shelf, 

 where it remained some days exposed to dust, and it crystallized from loss 

 of water by evaporation. 



P.S. August 17, 1871. — I may mention that the suggestion made 

 above, that in an open space far from houses the results would be still 

 more perfect, has been realized by exposing in such a space supersaturated 

 solutions of sodic sulphate and of alum in small shallow vessels, quite full, 

 to the action of a strong wind under a cloudy sky, and they did not crys- 

 tallize during half an hour's exposure ; but the moment they were touched 

 with the finger they became solid. Similar solutions were exposed ia 

 small open beakers in an open space during many hours, and at a tempe- 

 rature of about 40° F., without crystallizing. 



VII. "Note on the Spectrum of Encke's Comet." Ey William 

 Huggins, D.C.L., LL.D., V.P.R.S. Received November 16, 

 1871. 



I give the following observations of Encke's comet, and of the spectrum 

 of its light, in the order of the dates of the evenings on which they were 

 made. 



Oct 1 7. The comet presented the appearance of a nearly circular faint 

 nebulosity, in which no condensation could be certainly distinguished. 



Nov. 7. By this time an important change had taken place in the ap- 

 pearance of the comet. There was now a strong condensation of light 

 towards the east. The more condensed part of the comet, which was 

 fan-shaped, was bounded on the eastern side by a tolerably defined con- 

 tour, which approached in form to a parabolic curve. Surrounding this 

 brighter portion of the comet was a much fainter nebulosity, of which the 

 boundary on the eastern side appeared to form a line at right angles to the 

 axis of the comet. 



I suspected a very minute stellar nucleus just within the eastern extre- 

 mity of the brighter condensed part, and to a small extent north of the 

 comet's axis. 



Nov. 8. The description given yesterday is applicable to the comet to- 

 night. The brighter part appears more defined and in stronger contrast 

 to the fainter outlying nebulosity. The nucleus is now visible with cer- 

 tainty. On the western preceding side of the comet, the side towards the 

 sun, the cometary light becomes gradually fainter and more extended until 

 it is lost to view. 



On this evening the light of the comet was examined by the spectro- 

 scope. The larger part of the light was resolved by the prism into a 

 bright band in the green part of the spectrum. The band was defined at 



