DR L. BECKER ON THE SOLAR SPECTRUM. 



129 



At a glance it is apparent, that lines of equal intensity at medium altitudes increase 



differently in blackness as the sun approaches the horizon. If to each class of intensity 



at medium altitude we ascribe that intensity near the horizon, which is shown by the 



maximum number of lines in the preceding table, we obtain the values entered in the 



following table, where two numbers are given whenever the lines are clustered about two 



maxima : — 



Table VI. 





Intensity near Horizon. 



Intensity at Medium 















Altitudes. 



Wave-Length 



Wave-Length 



Wave-Length 



Wave-Length 



Wave-Length 



Wave-Length 





602 to 584. 



584 to 578. 



578 to 572. 



572 to 566. 



553 to 538. 



511 to 498. 







4-5 



3 5 



2-5 



6 



3-5 



6 



3-5 



4-5 



1 



5 



4 



35 



7 



4 



7 



35 



4-5 



2 



6 



4 



4 



8 



4-5 



8 



4 



5 



3 



8 



5 



4 







9 





5 



4 



9-5 

















5 



11 







... 











6 



12 

















From the fact that every class of intensity has a range of ±0*5 we shall show, that, for 

 some of the regions, the values given in this table explain the different behaviour of lines 

 of the same intensity at medium altitudes as exhibited in the Table V. 



Region A = 6020 to 5840. — Since intensity " 3 " for instance ranges from 

 intensity 2*5 to 3 "5, the preceding table shows that lines between 2*5 to 3 "5 at medium 

 altitudes give an intensity between 7 and 9 near the horizon. This range further 

 increases to 6"5 and 9*5 on account of the extent of each class of intensity. Without, 

 therefore, admitting any error in the estimations of intensity, we find thus, that lines 

 of intensity " 3 " at medium altitudes may increase near the horizon to any intensity 

 between 6"5 and 9'5. According to Table V., at least 47 lines out of 65 fulfil this con- 

 dition. But there are errors in the adopted intensities which will increase this range 

 considerably. We have to bear in mind that the single estimations of intensity of the 

 telluric lines vary with the altitude of the sun, and in this region, as we may anticipate, 

 with the amount of water -vapour, and that the adopted intensities are chosen to cor- 

 respond to a uniform altitude of the sun and an average amount of water-vapour. 

 These reductions entail, of course, a considerably larger error than is met with for the 

 solar lines (comp. Table III.). If it be permissible, therefore, to ascribe to every 

 class of intensity a range of ±1 instead of ±0*5 in high sun as well as in low sun, 

 we find, by analogous reasoning, that lines of adopted intensity " 3 " at high sun 

 should develope near the horizon into lines of intensity 5 to 10 '5, with the restriction 

 that the number of lines of each class within this range increases towards the middle 

 of the range. With this extension of our scale there are but 3 lines left out of 65, of 

 which the intensity at low sun falls beyond this range. Two of these three alter but one 

 class of intensity near the horizon, and one as much as eight classes. With regard to 



