184 



Mr. J. Norman Lockyer. 



will not fill the interspaces to the same degree that the hydrogen does, 

 there will be no masking of the dark lines by radiation. 



4. The Widening and Thinning of certain Lines. — In consequence of 

 the great difference of velocity and direction of the meteorites enter- 

 ing a swarm, the spectrum lines involved will in general be broader, 

 and therefore dimmer, so far as this cause is concerned, than in stars 

 where bombardment has ceased. Such a broadening was specially 

 noticeable in the spectrum of Nova Aurigaa, as I pointed out in a 

 paper communicated to the Royal Society on February 11, 1892.* 



The conditions, however, may vary considerably in different cases, 

 according to the character of the parent nebula. In the case of a 

 swarm which originally had a spiral structure, the chief movement 

 will be very similar to one of rotation ; if the axis of rotation be 

 directed towards the earth, such a movement will produce little or 

 no effect on the widths of the lines, but if the axis be not so placed, 

 different amounts of broadening would be produced, according to the 

 inclination and radial velocity. In these cases, lines which would be 

 sharp at the edges when there was no movement, would remain 

 sharp at the edges when broadened and dimmed. 



When the original nebula was of less regular form, the influx of 

 meteorites towards the centre will take place in a greater variety of 

 directions, so that the broadening effects will be less regular. 



Actions of this kind, in addition to those already referred to in 3, 

 are probably to some extent responsible for the generally greater 

 breadth of the metallic lines in bodies of increasing temperature as 

 compared with those in cooling stars of the same mean temperature. 



£ Tauri is an interesting case in point. "While the lines of 

 nydrogen are quite sharp and not very broad, those of the cleveite 

 gases are greatly distended and relatively dim. In this case, there- 

 fore, it would appear that the cleveite gases are more involved than 

 hydrogen in the highest temperature collisions. In /3 Lyrae, also, 

 the bright lines of the cleveite gases are more intense than those of 

 hydrogen, and here we have another indication that these gases are 

 among those chiefly involved in the spectral phenomena at the 

 highest temperature ; further, there is direct evidence that there are 

 at least two bodies in the system of ft Lyree, and the variability is 

 probably due to collisions between the outlying meteorites. 



It may, on the other hand, be that the lines in the spectra of some 

 cooling stars may be broadened as an effect of rotation, as suggested 

 by Professor Pickering in the case of a Aquilae. My own photo- 

 graphs show that the spectrum of this star is almost identical with 

 that of /3 Arietis, except that all the lines are broadened. In this 

 and similar spectra, such as a Ophiuchi and cc Cephei, the broadening 

 is accompanied by a reduction in intensity. 



* ' Koy. Soc. Proc.,' vol. 50, p. 434. 



