OF ARTS AND SCIENCES. 



245 



TABLE I. — Continued. 



No. 



04 



Date. 



1881-82. 

 July 17 



*G.J July 17 

 i'M July 21 



July 23 



08 July 24 



09 Aug. 8 



70 Aug. 12 



71 Aug. 14 



72 Aug. IG 



73 Aug. 23 



Mar. 23 



Mar. 25 



6[ Mar. 28 



Mar. SO 



Object. 



'78 



1882 

 Aug. 18 



Time. 



a tcorpii 



Moon 



a Lyras 

 JIoou 

 u. Scorpii 



a Aquilae 

 a Aquilas 



a Soorpii 



Jloon 



a Lyrx 

 a Lyrte 



Moon 

 a SJcorpii 



a Lyrse 



Jloon 

 a Scorpii 



a Lyra; 



Ncl'.ul.'i 

 ia Orion 



Nebulii 

 iu Orion 



Nebula 

 in Orion 



Nebula 

 iu Orion 



Moon 

 a Aquilw 



lOh. 



to 



llh. 47m. 



9h. 44m. 



to 

 12h. 7m. 

 llh. 40m. 



to 

 12h 2in. 

 9h. 17ui. 



to 

 lOh. 5Gm. 

 Oil. 30m. 



to 

 lOh. 4Gm. 

 10h.4Im. 



to 



llh. 47m. 

 8U. 27m. 



to 

 81i. 45m. 

 llh. 25m. 



to 



131i. 32m. 

 8h. 7m. 



to 

 lOli. 8m. 

 71i. 23in. 



to 

 9h. 14m. 

 7u. lorn. 



to 

 9h. 27m. 

 7U. 25m. 



to 

 Oh. 25m. 

 71i. 25m. 



to 

 'jh. 25m. 



Expos.' 81it. 



90m. 



15m. 



47m. 

 20m. 

 9Um. 



43m. 



53m. 



20m. 



49m. 

 44 m. 



20m. 

 Iftm. 



46m. 



14m. 



U4m. 



41m. 

 111m. 



131m. 

 120m. 

 120m. 



Im. 

 50m. 



.005 



.005 



.005 

 .005 

 .008 



.008 



.004 



.003 



003 

 .003 



.003 

 .(lOG 



.003 



.003 

 .003 



.003 



.017 



.012 



012 

 .004 



Inst. 



11-in, 



11-in. 

 11-in. 

 11-in. 



11 in 



11-in. 



Kemarks. 



11- 



11-in. 



11-in. 

 11-in. 



11-in. 



11-in 



11-in. 

 11-in 



11-in. 



11-iu 



11-in. 



11-in. 

 11-in. 



Although the night was unusu.-illy clear, 

 there was no impression of tlie spec- 

 trum of a Scorpii. ]t may have been 

 overlapped by the moon. 



a Scorpii very faint. 



At 12 h. 2 m. the sky clouded over. 



The night was not transparent. The 

 haze iu tlie sky sometimes almost con- 

 cealed the star- 

 Notwithstanding there was a white haze 

 in the sky. these spectra are very 

 sharp. 

 Night clouded over. 



At 8 h. 45 m. the night became cloudy. 



After the exposure of a LyrjB, had to 

 wait an hour for the moon to be high 

 enough tn get its spectrum. 



Tlie evening was misty, with clouds to 

 the north. 



This photograph of the spectrum of the 

 Nebula in Orion, and also tlie one of 

 March 25th, were taken without a slit, 

 and with a direct vi.-ion prism in the 

 cone of rays from the objective, before 

 they had reached a focus. 



Tliis spec trum of the Nebula in Orion 

 and the one of March oOth were taken 

 with the two-prism stellar spectro- 

 scope. 



This photograph was taken with a spec- 

 troscope compo.=ed of an Iceland spar 

 prism of two inches aperture, and two 

 quartz lenses of 15 inches focus and 

 also two inches aperture. This spectro- 

 scope is much more transp.-irent to the 

 photographic r.ays than the one witli 

 glass lenses and prisms, but it does not 

 give as good definition. 



Several of these pliotograph.s, as stated above, were taken to the 

 Harvard College Observatory in tlie spring of 1883, when the meas- 

 nrenients described below were made. This work may be divided into 

 throe parts : first, the determination of the relative positions of the 

 lines in the varions spectra in terms of any convenient unit of length ; 

 second!}', from the known spectra of the Moon and Jupiter, a determina- 

 tion of the relation of these measures to wave-lengtlis ; thirdly, a reduc- 

 tion of the measures of the stellar spectra to wave-lengths, and a 



