1888.] of the various Species of Heavenly Bodies. 



49 



A recent photograph of the region in Cygnus, previously known to 

 contain four spectra exhibiting bright lines, has served to bring to 

 our knowledge four other spectra of the same kind. One of these is 

 that of the comparatively bright star P Cygni, in which bright lines, 

 apparently due to hydrogen, are distinctly visible. This phenomenon 

 recalls the circumstances of the outburst of light in the star T Corona?, 

 especially when the former history of P Cygni is considered. Accord- 

 ing to Schonfeld, it first attracted attention, as an apparently new 

 star, in 1600, and fluctuated greatly during the seventeenth century, 

 finally becoming a star of the fifth magnitude, and so continuing to 

 the present time. It has recently been repeatedly observed at the 

 Harvard College Observatory with the meridian photometer, and does 

 not appear to be undergoing any variation at present. 



Another of the stars shown by the photograph to have bright lines 

 is D.M. + 37° 3821, where the lines are unmistakably evident, and 

 can readily be seen by direct observation with the prism. The star 

 has been overlooked, however, in several previous examinations of 

 the region, which illustrates the value of photography in the detection 

 of objects of this kind. 



The other two stars first shown by the photograph to have spectra 

 containing bright lines are relatively inconspicuous. The following 

 list contains the designations according to the ' Durchmusterung,' of 

 all eight stars, the first four being those previously known: — 35° 

 4001, 35° 4013, 36° 3956, 36° 3987, 37° 3821, 38° 4010, 37° 3871, 35° 

 3952 or 3953. Of these 37° 3171 is P Cygni, and 37° 3821, as above 

 stated, is the star in the spectrum of which the bright lines are most 

 distinct. 



[Received March 28, 1888.] 



Part IY. — Sub-groups and Species of Group II. 

 1. General Discussion of Duner's Observations. 



In the paper communicated to the Royal Society last November 

 I pointed out that the so-called " stars " of Class Ilia were not masses 

 of vapour like our sun, but swarms of meteorites ; the spectrum being 

 a compound one, due to the radiation of vapour in the interspaces and 

 to the aborption of the light of the red- or white-hot meteorites 

 by vapours volatilised out of them by the heat produced by colli- 

 sions. 



I also showed that the radiation was that of carbon vapour, and 

 that some of the absorption was produced by the chief fiutings of Mn 

 and Pb. 



These conclusions were arrived at by comparing the wave-lengths 

 of the details of spectra recorded in my former paper with those of 



VOL. XLIV. E 



