

xxvii.] THE IRON ARC IN HYDROGEN. 399 



The tables at the end of the above abstract, show how very 

 simple is the result obtained in Messrs. Liveing and Dewar's 

 very interesting experiments. We get an increase of absorption 

 when the conditions are favourable to the lives of the absorbing 

 molecules, wild tout. 



The results throw light in addition on some of the questions 

 which the experimenters had in their minds when the experi- 

 ments were undertaken, including the theoretical view that alter- 

 ations of temperature cannot put a stop to any of the fundamental 

 vibrations of a molecule. It is clear that the vibrations which 

 produce absorption are put a stop to in the case of iron for 

 instance, when no absorptions are seen, although they exist when 

 the absorption of 140 lines is seen. One inference at all events 

 is that the molecules themselves are " put a stop to " under the 

 conditions of the naked arc. It must be said at the same time 

 however that the " study of phenomena produced by such 

 mixtures of vapour as exist in our crucibles" from which 

 they hoped so much touching the " probable explanation of 

 the variations observed in the spectra of sun-spots and the 

 chromosphere " does not help us in that direction in the least. 



With regard to the sun-spot spectra I may remark, that I 

 have discussed the absorption lines of iron in hydrogen observed 

 by Messrs. Liveing and Dewar in connection with the Kensing- 

 ton sun-spot observations. In the region included from F to b 

 according to Thalen's new list there are 155 lines of iron. Of 

 these fifty-nine have been seen among the most widened lines of 

 iron at the sun-spot minimum. Over the same region Messrs. 

 Liveing and Dewar have seen reversed ten, all of which have 

 been seen among the most widened lines at different times. 

 If temperature then has not put a stop to the vibrations of the 

 remaining 145, it would be interesting to imagine what cause is 

 more probable than the one I have suggested, and it evidently 

 would be a very important experiment to see what the 

 absorption in a larger crucible would give us. 



