542 



SCIENCE 



[N. S. Vol. XLV. No. 1169 



Fig. .32. Eepresentative Spectra of Bright-line Nebulfe, pliotograplied by Wriglit 

 with the Mills spectrograph and 36-iuch refracting telescope of the Lick Observ- 

 atory. 



and dark lines of hydrogen. There are 

 hundreds of stars whose spectra contain a 

 wide variet3r of bright lines and dark lines. 

 Now and then a star's spectrum consists 

 almost wholly of bright lines, as in the ease 

 of Eta Carinse (Fig. 31). The bright lines 

 in stellar spectra tell us that their stars 

 contain extremely extensive atmospheres of 

 the gases and vapors hydrogen, helium, and 

 so on. A close relationship exists between 

 the Class B stars, with and without bright 

 lines, and a class of stars found extensively 

 in the Milky Way structure whose spectra, 

 containing many bright lines, are known as 

 Wolf-Rayet spectra, after the discoverers of 

 the first few stars in the class. Now, as 

 Wright has shown, the central stars in the 



planetary nebula? are of the Wolf-Rayet 

 type (see Fig. 32, B.D + 30° 3639) in 

 nearly all cases, and in other eases their 

 spectra are closely related to Class B 

 spectra (.see Fig. 32, N.G.C. 2932). It has 

 been shown, also chiefly by Wright, that the 

 spectra of the nebulous parts of the plane- 

 tary nebulffl have manj'' points of connec- 

 tion with the spectra of their central stars. 

 The spectra of the planetary nebulre and 

 the spectra of those large extended nebulse 

 (see Fig. 32, Orion, etc.) which give bright 

 lines are essentially alike in character. The 

 nebulium lines of the nebulfe have never 

 been found to exist in any true star, no mat- 

 ter what its class, and we leave them out of 

 account in this discussion; they do not in- 



