OF ARTS AND SCIENCES. 



253 



employed. As this instrument is corrected for the photographic rays, 

 the spectra are of nearly uniform width, becoming slightly narrower 

 at the ends. The other plates measured were obtained with the 

 28-inch reflector. As such an instrument is free from chromatic aber- 

 ration, the spectra are of uniform width. 



The measurements of the various spectra are given in Table VII. 

 The first column gives a number for reference, followed by the meas- 

 ures of the corresponding lines in the columns headed by the number, 

 of the plates. The second part of each portion of the table gives the 

 mean wave-length of each line, found by reducing the corresponding 

 measures to wave-lengths by means of the curve and correcting by 

 Table VI. The last columns give the residuals found by subtracting 

 the mean from the individual values. So many measures were made 

 of a LyrcB that the second part of the table is here separated from the 

 first. In Plate 73 the residuals are omitted, since the scale for this 

 plate differs from that of the others. In the spectra of a Scorpii on 

 Plate 73 the H line is not visible. The original readings are therefore 

 given in Table VII. 



TABLE Vn. 



a Aqcil.e. 



