1868.] 



Constitution of the Sun and Stars. 



17 



Section III. — Of the Outer Atmosphere of the Sun. 

 27. Such, then, is the order in which we should expect to find that 

 those of the elements which exist in the sun's atmosphere succeed one 

 another, — the atmosphere of hydrogen far overlapping all the rest ; then, 

 at a profound depth, sodium and magnesium, reaching nearly to the same 

 height, since the masses of their molecules are nearly equal ; next, at a 

 great distance further down, calcium ; then, in a group reaching nearly to 

 the same height, chromium, manganese, iron, nickel, and cobalt ; then, 

 within a moderate distance of these, copper and zinc ; and lastly, after a 

 vast interval, barium. These are all the elements as yet known to exist in 

 the sun's atmosphere. Let us now compare with the observations this 

 anticipation founded on the molecular constitution of the elements, bear- 

 ing in mind that the order is likely to be in some few cases incorrect, 

 owing to our having occasionally erred in assigning the foregoing masses to 

 the vapour-molecules. To make this comparison most effectually, Table II., 

 opposite top. 32, of the intensities of the solar lines observed by Kirchhoff 

 will be of use. In this Table the lines of each known constituent of the 

 solar atmosphere are placed in the order in which they occur in the parts 

 of the spectrum mapped by Kirchhoff, which extend between wave-lengths 

 43 and 77 eighth-metres, that is from the indigo about G to the extreme 

 crimson beyond A*. Each spectral line is represented by a number, 



* The reader should have by him Kirchhoff's maps of the solar spectrum in illustra- 

 tion of this paper. They have been published in a separate form by Messrs. M'Millan 

 and Co. It will make a reference to these exquisite maps much easier, not only for the 

 purposes of this memoir, but also for many other purposes, to mark with pencil-dots 

 upon Kirchhoff's arbitrary scale each of the following positions of an absolute scale, 

 founded upon Angstrom's determinations of the wave-lengths of 70 lines (see Poggen- 

 dorff s ' Annalen,' 1864, vol. iii., or Phil. Mag. 1865, vol. i.). 



Positions upon Kirchhoff* s scale of the principal points of a scale xvhich expresses the 

 lengths of the light-waves in air. 

 (N.B. Those positions which have a note of interrogation after them are doubtful, as 

 they are too distant from rays measured by Angstrom to admit of a safe interpolation.) 



Wave-lengths 







Wave-lengths 







in 







in 







eighth-metres, 

 i. e. metres di- 





Kirchhoffs 



eighth-metres 





Kirchhoff's 





arbitrary 



i. e. metres di- 





arbitrary 



vided by 10 s . 





scale. 



vided by 10 s . 





scale. 



43 corresponds to 2873-1 



44-30 





2651-5 



43-10 





2855-0 



45 





2553-2? 



43-20 



J5 



2837-0 



46 



j> 



2422-0? 



43-30 



J5 



2819-0 



47 



>> 



2292-5 ? 



43-40 



J) 



2801-1 



48 



>> 



2164-0? 



43-50 



JJ 



2783-4 



48-50 



>> 



2099-8 



43-60 



5> 



2766-0 



48-60 



>> 



2086-7 



43-70 





2748-8 



48-70 



>> 



2073-7 



43-80 



>> 



2732-0 



48-80 





2060-8 



43-90 



>> 



2715-7 



48-90 





2047-9 



44 



5> 



2699-6 



49 





2035-2 



44-10 





2683-7 



49-10 





2022-6 



44-20 



5> 



2667-6 



49-20 





2010-2 



VOL. XVII, C 



