170 Mr. J. N. Lockyer. Researches in Spectrum [Dec. 12, 



brightness might be changed, and C might be the brightest and the 

 most persistent, and at a still higher temperature E." 



On these grounds Professor Stokes, while he regarded the facts I 

 mentioned as evidence of the high temperature of the sun, did not 

 look upon them as conclusive evidence of the dissociation of the mole- 

 cule of calcium. 



Since that paper was sent in, however, the appeal to the stars to 

 which I referred in it has been made, and made with the most admir- 

 able results, by Dr. Huggins. 



The result of that appeal is, that the line which, according to Pro- 

 fessor Stokes's view, should have prevailed over all others, as Sirius 

 is acknowledged to be a hotter star than our sun, if it exists at all in 

 the spectrum, is so faint that it was not recognised by Dr. Huggins 

 in the first instance. 



In Sirius, indeed, the H line due to one molecular grouping of cal- 

 cium is as thick as are the hydrogen lines as mapped by Secchi, while 

 the K line, due to another molecular grouping, which is equally thick 

 in the spectrum of the sun, has not yet made its appearance. 



In the sun, where it is as thick as H, the hydrogen lines have vastly 

 thinned. 



While this paper has been in preparation, Dr. Hnggins has been 

 good enough to communicate to me the results of his most important 

 observations, and I have also had an opportunity of inspecting several 

 of the photographs which he has recently taken. The result of the 

 recent work has been to show that H and h are of about the same 

 breadth in Sirius. In a Aquilas, while the relation of H to h is not 

 greatly changed, a distinct approach to the solar condition is observed, 

 K being now unmistakably present, although its breadth is small as 

 compared with that of H. I must express my obligations to Dr. 

 Huggins for granting me permission to enrich my paper by reference 

 to these unpublished observations. Hrs letter, which I have permis- 

 sion to quote, is as follows : — 



" It may be gratifying to you to learn that in a photograph I have 

 recently taken of the spectrum of a Aquilas there is a line correspond- 

 ing to the more refrangible of the solar H lines [that is K], but about 

 half the breadth of the line corresponding to the first H lines. 



" In the spectra of a Lyrse and Sirius the second line is absent." 



Professor Young's observations of the chromospheric lines, to which 

 I shall afterwards refer, give important evidence regarding the pre- 

 sence of calcium in the chromosphere of the sun. He finds that the H 

 and K lines of calcium are strongly reversed in every important spot, 

 and that, in solar storms, H has been observed injected into the chromo- 

 sphere seventy-five times, and K fifty times, while the blue line at 

 W. L. 4226*3, the all-important line at the arc temperature, was only 

 injected thrice. 



