OF ARTS AND SCIENCES. 141 



Yale College, and soon after left New Haven, when the research was 

 necessarily interrupted. I hoped, however, that the novelty and 

 interest of the observations might lead others, possessed of the neces- 

 sary apparatus, to develop the results of this method of investigation. 

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

 was glad to have an opportunity to continue the investigation in tlie 

 summers of 1879 and 1880. The results of my labor are embodied 

 in this paper. 



The method adopted in the recent observations is exactly the same 

 as that described in the article cited ; instead, however, of the equa- 

 torial 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 gentlemen 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 Rutherford grating on 

 speculum metal, either of 8,648 or 17,296 lines to the inch, at will. 

 These gratings were of the largest size, having a ruled surface of 

 about If in. square. 



The immediate results I give in the order of the refrangibility of 

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

 to anything other than the temporary modifications of transparency in 



o 



our atmosphere. The numbers are the places on Angstrom's maps, 

 as nearly as could be ascertained without a 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. 



(Z)i) 5894.8 slightly less hazy at limb. 



(Z)^) 5889.0 decidedly cleaner at limb. 



A fine line very close to its more refrangible side is either wanting 

 or much fainter in spectrum of limb. 



5577.5 is much stronger at limb. 



o 



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



The Mg. lines 5183.0, 5172.0, 5166.5 {b^ b.^ b^) are cleaner at 

 limb. The line b^, belonging to a different element, does not show 

 such a peculiarity. 



5045 (a faint line not in Angstrom) 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. 



