ON SCIENCE-LECTURES AND ORGANIZATION. 501 



every time one looks at the sun. These must be provided for, of course ; but 

 the great thing is not to lose time in starting the work in which time plays 

 the most important part. I think the future will show that in its broad 

 outline this work is as follows : — 



a. Observations on the Janssen-Lockyer Method. 



Prominences at limb : — 



1. Number. 



2. Position on sun, with reference to spots and faeulse. 



3. Height and brilliancy. 



4. Materials. 



5. Currents, direction, and velocity. 



6. Thickness of lines at top and bottom. 



Prominences on sun : — 



7. Number. 



8. Position (as above). 



9. Materials. 



10. Rate of elevation or depression. 

 10a. Width of lozenge, 



1 1 . Thickness and briUiancy of lines and associated bright lines in spectrum 

 of photosphere. 



Spots : — 



12. Lines thickened. 



13. Thickness of lines. 



14. Alterations of wave-length. 



15. Variations of spectrum near spots, including bright lines. 



Faeulse : — 



16. Thinning and disappearance of lines. 



17. Bright photospheric lines. 



b. Observations on Kirchhoff' s Method. 



18. Map frequently suspected regions of spectrum to detect changes in 

 Fraunhofer lines. 



19. Determine accurately every three or six months the thickness of the 

 principal Fraunhofer lines. 



20. Note changes in bright lines. 



If the Committee wish, I shall be happy to state at length the reasons 

 which have led me to consider these observations as of high importance and 

 of a secular nature. I may at once, however, very briefly point out, seeing 

 that observations of the spots are considered valuable on all hands, that as 

 the prominences occur in regions where the pressure is less than at the spot- 

 level, they will be likely to afford better indications of the fact of the solar 

 forces being at work ; and as there is reason to believe that they are connected 

 with the spots, we shall get more complete evidence in the same direction as 

 that given by the spots. But we may get very much more than this. We 

 now know that the sun's atmosphere extends 10' at least above the spot- 

 level ; we may therefore hope in this way to catch shorter periods than the 

 sun-spot periods. Again, the spectroscope takes us beyond the fact oi forces 

 being at work. The bright prominences and the lozenges seen on the sun 

 itself, the thickening of lines in spots, and the alterations of wave-length are 



