326 Geological Society : — 



8. At times, D puts on the appearance of the limiting line of a 

 channelled-space spectrum, the " easing off " of the absorption being 

 now on one side and now on the other. 



9. Should all these phenomena be ultimately referred to the 

 causes which produce a channelled-space spectrum (one of which 

 undoubtedly is the tendency to a unilateral instead of a bilateral 

 widening), a line-spectrum will be regarded as a special case merely, 

 and not as an entirely different spectrum, as it has been hitherto ; 

 and the range of molecular combinations in any one element from 

 which line-spectra may be produced is extended. 



10. The question further arises, whether many of the short lines 

 in spectra are not remnants of channelled-space spectra. 



June 18. — Joseph Dalton Hooker, C.B., President, in the Chair. 



The following communication was read : — 



l * Researches in Spectrum-Analysis in connexion with the Spec- 

 trum of the Sun." — No. IV. By J. Norman Lockyer, F.R.S. 



Maps of the spectra of calcium, barium, and strontium have been 

 constructed from photographs taken by the method described in a 

 former communication (the third of this series). The maps com- 

 prise the portion of the spectrum extending from wave-length 3900 

 to wave-length 4500, and are laid before the Society as a specimen 

 of the results obtainable by the photographic method, in the hope 

 of securing the cooperation of other observers. The method of 

 mapping is described in detail, and tables of wave-lengths accom- 

 pany the maps. The wave-lengths assigned to the new lines must 

 be considered only as approximations to the truth. Many of the 

 coincidences between lines in distinct spectra recorded by former 

 observers have been shown, by the photographic method, to be 

 caused by the presence of one substance as an impurity in the 

 other ; but a certain number of coincidences still remain undeter- 

 mined. The question of the reversal of the new lines in the solar 

 spectrum is reserved till better photographs can be obtained. 



GEOLOGICAL SOCIETY. 



[Continued from p. 243.] 



May 27th, 1874. — John Evans, Esq., F.R.S., President, 



In the Chair. 



The following communications were read : — 



1. " On the last Stage of the Glacial Period in North Britain." 

 By T. F. Jamieson, Esq., F.G.S. 



In this paper the author arranged the Glacial phenomena of Scot- 

 land under the following three heads : — 



1. The great early glaciation by land-ice (maximum effects of 

 glaciation). 



2. The period of glacial marine beds containing remains of 

 Arctic Mollusca, when most of the country was covered by 

 the sea. 



