Prof. S. P. Langley on the New Spectrum. 129 



Ultima Thule, this region, which he has ventured to call the 

 " New Spectrum," extends. It will be found between wave- 

 lengths l'S* and 5*3^ on the map. 



The speaker had been much indebted to others for the 

 perfection to which the apparatus, and especially the galvano- 

 meter, had been brought. He was under obligations 

 particularly to Mr. Abbot, for assistance in many ways, 

 which he had tried to acknowledge in the volume ; but 

 before closing this most inadequate account of it, he would 

 like to draw attention to one feature which was not represented 

 in the spectrum map before them, although it would be found 

 in the book. 



During early years the impression had been made upon 

 him that there were changes in the spectrum at different 

 periods of the year. Some of these changes might be in the 

 sun itself. The major portion of those he was iuimediatelv 

 speaking of, he believed, were rather referable to absorptions 

 in the earth's atmosphere. 



Now these early impressions had been confirmed bv the 

 work of the Observatory in recent years, and charts given in 

 the volume would show that (the sun being always supposed 

 to be at about the same altitude, and its rays to traverse 

 about the same absorbing quantity of the earth's atmosphere) 

 the energy spectrum was distinctly different in spring, in 

 summer, in autumn, and in winter. The lateness of the 

 hour prevented him from enlarging on this latter profoundlv 

 interesting subject. He would only briefly point out the 

 direction of these changes, which were not perhaps to be called 

 conspicuous, but which seemed to be very clearly brought 

 out as certainly existing. With regard to them he would 

 only observe, what all would probably agree to, that while 

 it lias long been known that all life upon the earth, without 

 exception, is maintained by the sun, it is only recently that 

 we seem to be coming by various paths, and among them by 

 steps such as these, to look forward to the possibility of a 

 knowledge which has yet been hidden to us of the way in 

 which the sun maintains it. We were hardly beginning to 

 see yet how this could be done, but we were beginning 

 to see that it might later be known, and to see that the 

 seasons, which wrote their coming upon the records of the 

 spectrum, might in the future have their effects upon the 

 crops prevised by means somewhat similar to those previsions 

 made day by day by the Weather Bureau, but in ways 

 infinitely more far-reaching, and that these might be made 

 from the direct study of the sun. 



Phil. Mag. S. 6. Vol. 2. No. 7. July 1901. K 



