I 



17 363 



For the determination of the relation hetween effective wavelength and colour 

 index In, 14 special plates were taken of stars contained in the Göttingen Actino- 

 metry. The data of these plates are given in Table 10 and the results of the 

 separate stars in Table 11. Least square solutions gave the following formulae 

 using first the colour index /h and then the effective wavelength / measured in 

 millimeters as argument: 



/- 1-10317 = -04983 (/h — -672) 

 and 



/h — -672 = 19-033 (/— 1-10317) 



The effective wavelength in Angström units is equal to 3944-2 /. Hence 



Jhfi/JlH= 197 and 207 or in the mean 202^». ± 13^/,,, (m. e.) 



Finally the value ^AeffAZ/n = 200 ^/m has been adopted, or 



/h = 19-721 (7— 1-0690) 

 Âeff = 200/H + 4216-4 



For the colour index derived from the effective wavelength the designation /^ 

 is used. ' 



1 1. Relation between the Effective Wavelengths found from 

 the Spectra of the \^\ 11"^ and Iir^ Order. 



The effective wavelengths found from the spectra of the II"'' and IIP'' order 

 were first converted into provisional values of /; by the aid of the formula derived 

 for the spectra of the P' order. Marking these provisional values with ' the following 

 relations were found empirically: 



/^, I = + -020 + -632 II „ + -1044 /i^n 

 and /;,i =— -084 + -617 7i_ III + -1482 /^^„i 



These formulae were used for the reduction of I'l u and liui to the sj'stem 

 /;^_i adopted in the present paper. 



12. Detailed Example of the Measures of Star No. 508. 



It was at first intended to print fbr each star the effective wavelength derived 

 from each separate exposure. For obvious reasons this idea has been abandoned. 

 The example given in Table 1 2 of the measures of the star no. 508, the 6*^/3'" 

 distant companion to Alcyone, will be sufficient to show the character of the observ- 

 ations. The first 4 columns of Table 12 refer to the spectra of the P' order, the 

 next 4 columns to those of the IP'' order and the last 4 columns to those of the 



D. K. D. Vidensk. Selsk. Skr., nalurv. og mathem. Afd., S. R.-ekUe. IV, 4. ^g 



