88 THE CHEM1STKY OF THE SUN. [CHAP. 



that is, 392 billions of waves entering our eye each second in 

 the case of red light, taking the line A in the spectrum, and 



29,800,000,000,000,000,000 



= 757,000,000,000,000 



39,328 



that is 757 billions in the case of violet light, taking K in the 

 spectrum. 



As the velocity of light is the same for all waves, it follows 

 that the number of waves per second varies inversely as the 

 wave-length in each case, and that the number of waves per 

 second multiplied into the wave-length of any particular line 

 must give us a constant quantity, namely, the velocity. 



In Angstrom's memoir 1 the wave-lengths are given to the 

 second decimal place, the unit being Tsinnnnn^h of a millimetre. 

 In the Atlas which accompanies this memoir the scale is 

 divided so that one division corresponds to TTrcro-Vwo-th of a 

 millimetre of wave-length. In addition to marking the wave- 

 lengths of the solar lines, their relative intensities are shown. 

 The map also gives the origin of each line and its correspond- 

 ence with the lines of metallic spectra so far as these have 

 been determined by Angstrom and Thalen. 



The first results 2 of Angstrom's comparison of the wave- 

 lengths of metallic vapours with the Fraunhofer lines added 

 the possibility of strontium and aluminium being among the 

 solar elements. He thus allocated the principal Fraunhofer 

 lines : 



H 1 and H? to Calcium. 



G ,, Iron 



F ,, Strontium and Iron (uncertain). 



b ,, Magnesium and Iron. 



D Sodium. 



C Hydrogen. 



B Potassium. 



1 Recherches sur le Spectre Solaire, TJpsala, 1869. 



2 Communicated to the Eoyal Academy of Stockholm, Oc tober 8, 1861. Phil. 

 Mag. vol. xxiv. s. 4, p. 1. 



