DR L. BECKER ON THE SOLAR SPECTRUM. 



137 



work on the solar spectrum. It comprises the whole region from A to b, and gives the 

 solar lines as well as the water-vapour and dry-gas lines. M. Thollon has observed 

 (in the years 1883 to 1887?) not only the positions and intensities of the lines but 

 also their breadth in various altitudes of the sun. They are reduced to four states. 

 The first refers to a zenith-distance of the sun of 80° when the air contains little 

 water- vapour ; the second and third correspond to a zenith-distance of 60° when the 

 air is either almost saturated with water-vapour or very dry the fourth gives the 

 solar lines only. The charts are drawn by M. Thollon, and are really a work of art. 



As the observations are not reduced to wave-lengths we could not compare the positions 

 of the lines with our own, but to judge from the maps the agreement appears to be very 

 close in all the parts compared. M. Thollon finds the same groups of water- vapour lines 

 as we have given above. There are, however, some telluric lines which our observations 

 do not attribute to atmospheric absorption, as for instance lines between A = 5295 and 

 5292 i.U. 



As to detail, we must say that the Rowland grating, combined with the large collimator 

 and viewing telescope, has proved its superiority over a prismatic train. M. Thollon 

 employed a spectroscope with a set of bisulphide of carbon prisms. The telluric lines are 

 also more numerous in our observations. This we are inclined to attribute to the great 

 depth of atmosphere in which our observations were obtained. This is shown by the 

 following summary : — 





Number of Solar and 



Number of Telluric 







Telluric Lines. 



Lines. 





Portion of the Spectrum. 









Thollon. 



Becker. 



Thollon. 1 



Becker. 



6020-5840 



456 



574 



326 



376 



Rain-band 



5840-5780 ) 

 5780-5720 V 

 5720-5660 ) 



370 



613 



( 23 



<^ 66 

 ( 44 



109 ( 

 117 j ) 

 76 j 



Supposed oxygen band 

 Water-vapour band 8. 



5660-5530 



246 



396 



1 



2 





5530-5390 



314 



447 



46 



106 



Water-vapour band £. 



5390-5250 



328 



428 



9 



19 





5250-5167 



178 



272 









1 On p. A15, loc. cit, there is a table of water-vapour lines in which the figures do not agree with those given above. 

 M. Thollon gives 107 telluric lines more than we counted from the hook. We reproduce his summary : — 



Longueurs d'ondes. 



Nombre de raies 

 telluriques. 



Mixtes. 



0-597-0-585 

 0-578-0-567 

 0-548-0-542 



319 



118 

 40 



72 

 15 

 18 



