92 Mr. C. B. Hastings's Theory of 



results gained by its use were described in a note, " On a com- 

 parison of the spectra of the limb and the centre of the Sun," 

 published in Silliman's Journal, vol. v. (1873), pp. 369-371. 

 I was then a student at Yale College, and soon after left New 

 Haven, when the research was necessarily interrupted. I 

 hoped, however, that the novelty and interest of the observa- 

 tions might lead others, possessed of the necessary apparatus, 

 to develop the results of this method of investigation. But as 

 nothing as been published on this subject since that time, I 

 was glad to have an opportunity to continue the investigation 

 in the summers of 1879 and 1880. The results of my labour 

 are embodied in this paper. 



The method adopted in the recent observations is exactly 

 the same as that described in the article cited ; instead, how- 

 ever, of the equatorial of the Sheffield Scientific School, I 

 used a Clark equatorial of 9*4 in. aperture and 120 in. focal 

 length, which was kindly placed at my disposal by the gentle- 

 men in Hartford, to whom it belongs*. The New-Haven 

 spectroscope, too, of twelve effective prisms, was replaced by 

 one of which the dispersing member was a Rutherfurd grating 

 on speculum-metal, either of 8648 or 17,296 lines to the inch 

 at will. These gratings were of the largest size, having a ruled 

 surface of about If inch square. 



The immediate results I give in order of refrangibility of 

 the lines observed, as no observed variations in them can be 

 attributed to any thing other than the temporary modifications 

 of transparency in our atmosphere. The numbers are the 



places on Angstrom's maps as nearly as could be ascertained 

 without micrometer. 



Line (C) 6561*8 is cleaner and wider at limb ; i. e. the haze on 

 either side of the line as ordinarily seen is much reduced. 



6431 is slightly stronger at centre than at limb. 



6371 is visible at centre but not at limb. 



(D x ) 5894-8 slightly less hazy at limb. 



(D 2 ) 5889*0 decidedly cleaner at limb. 



A line line very close to its more refrangible side is either want- 

 ing or much fainter in spectrum of limb. 



5577'5 is much stronger at limb. 



5440 + (not on Angstrom's chart) is a little stronger at limb. 



The Mg lines 5183-0, 5172*0, 5166-5 (\b 2 bj are cleaner at limb. 

 The line & 3 , belonging to a different element, does not show such a 

 peculiarity. 



5045 (a faint line not in A.) is stronger at limb. 



* My acknowledgments for this courtesy are gratefully accorded to 

 Mr. Edgecomb, its former owner, and to Mr. Howard and Mr. Chapin, its 

 present owners. 



