1881.] On the Spectra of Sun-spots. 203 



o 



to the arc and spark at wave-length 4703 does not appear in Angstrom's 

 map. It is hard to account for its absence, as it is present in Kirch- 

 hoff's map and in Rutherford's photograph. We have noticed, however, 

 that when the spark is taken in hydrogen, the line at wave-length 4570 

 appears stronger than that at wave-length 4703, while the reverse is 

 the case when the atmosphere is nitrogen. It is possible then that 

 the atmosphere may, besides the resistance it offers to the discharge, 

 in some degree affect the vibrations of the metallic particles.. 



When we have made all the simplifications that we can by elimi- 

 nating, as we hope we have done satisfactorily, the hydrogen- magnesium 

 flutings, and by supposing the whole series of triplets to be harmoni- 

 cally related, and possibly some of the single lines also to be similarly 

 related, we have still the fact that the chemical atoms of magnesium 

 are either themselves capable of taking up a great variety of vibra- 

 tions, or are capable by mutual action on each other, or on particles of 

 matter of other kind, of giving rise to a great variety of vibrations of 

 the luminiferous ether; and to trace satisfactorily th 3 precise con- 

 nexion between the occurrence of the various vibrations and the 

 circumstances under which they occur, will require yet an extended 

 series of observations. 



IV. " Note on the Reduction of the Observations of the Spectra 

 of 100 Sun-spots observed at Kensington." By JL Norman 

 Lockyer, F.R.S. Received May 12, 1881. 



[Plate 2.] 



In anticipation of a more detailed communication, I beg to> lay 

 before the Royal Society some of the results of the reduction of the 

 six most widened lines between F and b seen in the spectra of 100 

 sun-spots, observed at Kensington between November 12th, 1879, and 

 September 29th, 1880, limiting my remarks solely to the spectrum of 

 iron. 



In the accompanying map, the Fraunhofer lines agreeing in 

 position with the iron lines given by Angstrom and Thalen are 

 entered in the horizon headed " Sun," in the next are plotted the 

 lines assigned to iron by Angstrom, who used the electric arc in his 

 experiments. In the next horizon are entered the iron lines given by 

 Thalen, who employed the induction coil in his experiments. In these 

 three horizons the lengths of the lines represent their intensities. 



The individual observations of the sun-spots having been plotted out 

 on another map, the number of times each line was seen was ascer- 

 tained, and is entered in the next horizon under " Frequencies in Sun- 

 Spots." 



