60 Royal Society : — 



intense the dark gaps produced by the vapours in the stronger light 

 of all refrangibilities which is evidently present. 



What is the source of the light in the umbra which gives the con- 

 tinuous spectrum ? May the dense and intensely heated gases, which 

 probably form the inner substance of the sun, emit, in some cases, 

 lines so greatly expanded as to form, when numerous spectra are 

 superposed, a sensibly continuous spectrum ? Dr. Balfour Stewart 

 has suggested that, as gases possess a power of general absorption 

 of light, a heated mass of gas, if sufficiently dense to be opaque or 

 nearly so, would give a continuous spectrum as well as the spectrum 

 of bright lines peculiar to it. 



" On the Spectrum of Brorsen's Comet, 1 868." By William 

 Huggins, F.R.S. 



In January 1866 I communicated to the Royal Society the result 

 of an examination of a small comet visible in the beginning of that 

 year*. I examined the spectrum of another small and faint comet 

 in May 1867. The spectra of these objects, as far as their very feeble 

 light permitted them to be observed, appeared to he very similar. In 

 the case of each of these comets, the spectrum of the minute nucleus 

 appeared to consist of a bright line between b and F, about the po- 

 sition of the double line of the spectrum of nitrogen, while the ne- 

 bulosity surrounding the nucleus and forming the coma gave a spec- 

 trum which was apparently continuous. 



Unfavourable weather prevented me from obtaining an observa- 

 tion of Brorsen's comet, at its present reappearance, before April 29. 

 Since that evening I have examined it on May 2, 4, 6, 7, 12, 13. 

 As I have not noticed any change in its spectrum during this time, 

 I will put together the results of my observations on different nights, 

 in order to avoid the repetition which would occur if the observa- 

 tions were arranged in the order in which they were made. 



I tried various spectroscopes upon this object. The best views 

 of its spectrum were obtained with a spectroscope of the form already 

 described in my former paperst, and furnished with one prism of very 

 dispersive flint glass, with a refracting angle of 60°. Some measures 

 were taken with a similar spectroscope with two prisms of 60°. 



The comet appears in the telescope as a nearly round nebulosity, 

 in which the light increases rapidly towards the centre, where on 

 some occasions I detected, I believe, a small stellar nucleus. Gene- 

 rally this minute nucleus was not to be distinguished from the bright 

 central part of the comet. I suspected two or three bright points in 

 the coma. May 7, I perceived a small extension of the faint sur- 

 rounding nebulosity in a direction opposite to the sun, so as to form 

 a short tail. 



The spectrum of this comet consists for the most part of three 

 bright bands. The length of the bands in the instrument shows that 

 they are not due alone to the stellar nucleus, but are produced by 

 the light of the brighter portions of the coma. 



* Proceedings of the Royal Society, vol. xv. p. 5. 

 t Philosophical Transactions,. 1864, p. 415, &c. 



