OP ARTS AND SCIENCES. 259 



The only line omitted in this table which was noted in the spectra of 

 a Aurigce or a Bootis is No. 69 of Table VII. This line was meas- 

 ured in Plate 23 as one edge of a dark band in the negative, No. 70, or 

 h, forming the other side. Its wave-length may therefore be taken as 

 about 4090. This is the bright band noted on page 242. The same 

 phenomenon is shown in Plate 24, and even better in Plate 32. It 

 is also noticeable, though in a less marked manner, in the solar spec- 

 trum, as is shown in the photographs of Jupiter and of the Moon. 



Not only do the lines of a Aurigce and a Bootis appear to coincide 

 with those of the Sun in position, but their relative intensity seems to 

 be nearly the same. Of the twelve lines seen in at least seven of the 

 nine spectra of the Moon and Jupiter, every one is contained in the 

 spectra of both a Aurigce and a Bootis. Of the fifteen lines which are 

 so faint as to be contained in but one or two of the spectra of the Moon 

 or Jupiter, only four are contained in the spectrum of a Bootis, and 

 but one in that of a Aurigce. The evidence afforded by the.-e photo- 

 graphs, therefore, points very strongly to the conclusion that tlie spec- 

 tra of these stars, and consequently their constitution, are the same as 

 that of our Sun. 



The measurements of a Scorpii are much less satisfactory than 

 those of the other stars. Plate 73 gives a large number of lines, but 

 the scale of this plate, as already stated, differs from that of the 

 others. Fortunately, a Lyrce was photograped on the same plate, and 

 a curve was accordingly constructed with the measurements of the 

 lines of this star as abscissas, and the wave-lengths taken from the 

 measures of the other plates as ordinates. By this curve the meas- 

 ures of a Scorpii were reduced. Plates 39 and 48 were taken with a 

 wide slit, and the lines are indistinct. A satisfactory comparison 

 could scarcely be made without preparing enlarged paper positions, 

 and marking on them the points measured. This seems scarcely 

 advisable, considering the superiority of Plate 73. The large residuals 

 render the identification uncertain in some cases, since any line would 

 fall near one of those in Plate 73. The correspondence is much less 

 marked than in the other stars. 



A comparison of the measures of the various plates is given in 

 Tabic X. The first column gives the number of the plate ; the sec- 

 ond, the name of the object photographed ; the third, the number of 

 measures made, that is, the number of points of the spectrum noted ; 

 and the fourth column gives the quantity subtracted from each of the 

 measures to reduce them to the same zero. The measures of the ends 

 of the spectra are given in the next two columns, followed by the 

 reduced value in wave-lengths. 



