OF ARTS AND SCIENCES. 



251 



Plate 42 was one of the first to be measured, and only the most 

 conspicuous lines were observed. This was done with the intention of 

 determining the scale from a few well-defined lines. It was afterwards 

 deemed better to employ all the lines visible on each plate for this 

 purpose. No marked line in the solar spectrum satisfactoi-ily repre- 

 sents No. 4 of Table IV. Nos. 3 and 4, 5 and 6, and 7 and 8, are des- 

 ignated in the original record as the limits of transparent bands in the 

 negatives, that is, of dark bands in the spectrum. Nos. 11 and 12 

 appeared as a broad dark band, whose edges were observed in Plate 

 65, and its centre in Plates 21, 24, 35, and 43. No. 28 is recorded in 

 Plate 57 as the centre of the band extending from 27 to 29. No. 47 

 is not well identified. The photographs of the solar spectrum indicate 

 a line having A = 4375 as the most conspicuous in this vicinity. 



The residuals in Table IV. must next be examined, to see if they in- 

 dicate any systematic deviation, or if any correction should be applied to 

 the wave-lengths as deduced by the formula A = 3672 -\- 30 n -\- 4tr. 



In Table V. they are arranged in groups extending from 3750 to 

 3850, 3850 to 3950, etc. The first column gives the approximate 

 mean wavelength of each group, and the next four columns give for 

 the Moon the number of measurements included in each group, the sum 

 of the positive and the sum of the negative residuals, and their alge- 

 braic mean. The next four columns give the corresponding quantities 

 for Jupiter. The last three columns relate to the observations of the 

 Moon and Jupiter, without distinction. The first of these columns gives 

 the algebraic mean of all the residuals, and indicates the observed 

 deviation from the computed wave-lengths. A curve was drawn to 

 represent this deviation, and its ordinates are given in the next column. 

 Finally, the residuals were all corrected by means of this curve accord- 

 ing to the system indicated in Table VI., and the arithmetical mean of 



