August 4, 1881] 



NA TURE 



o-'o 



indications of excessively complex groupings which are ju-t dying 

 at the temperature we are using at the time. So that if it may 

 be permitted ta coin terms I should like to call some of the 

 short lines hot-short lines, and others cold-slurt lines. Wesha'l 

 see the reason by and by. 



Now if this order of things is in any way as I have stated it, 

 the first test that we have to employ is one of excessive sim- 

 plicity. The differences between terrestrial and solar spectra 

 indicate that if the view be correct differences should be seen in 



the spectra of the same substances observed in different parts of 

 the sun. 



We should now have a very distinct notion of the enormous 

 difference of temperature between the highest and lowest 

 reaches of the solar atmosphere. The lowe t region of the 

 solar atmosphere that we can get at must be far hotter than the 

 highest part «e can get at, at all events in times of eclipses ; the 

 lines that we should see therefore in the hottest region of the 

 sun should bring us very near to the effects of this transcendental 



SPARK THALEN 



-'" 'FREQUENCIES 



50 1 SUN SPOTS 



^o\ KENSINGTON 



teaiperature to which I have referred, and the spectrum of iron 

 seen in this way should bring us in presence of the result of the 

 highest temperature. 



Let Us take then the storms as giving us the spectrum of the 

 hottest part of the sun. "Where are we to find the record of the 

 coolest part ? Now to get to this point we have had naturally 

 to dimiss all the observations which have been made of the 

 lines visible in solar prominences, of the lines thickened in solar 

 spots and the like, because we kaow that in these prominences 



and spots we really are dealing witli phenomena local to par- 

 ticular and highly heated regions. 



Dealing with the whole solar spectrum we know that we are 

 dealing with the whole of the solar atmoiphere, however great, 

 however high that atmosphere must be. Therefore we know 

 that the solar atmospheric spectrum, the Frauahofer spectrum, 

 cannot by any possibility give us what is going on in any parti- 

 cular region— it must naturally be the summation of what is 

 going on in every region where any absorption of any kind 



