M. A. J. Angstrom's Optical Researches. 



331 



trum is based are contained in the following table. It is to be 

 remarked, tbat the measurements for the different metals were 

 not determined at once, but that the prism was so fixed for each 

 series that the line D gave the minimum of deflection*. 



In order to calculate the indices of refraction, and from 

 them the wave-lengths which correspond to the principal lines 

 of the spectrum, I have measured the absolute deflections of 

 some of them ; two spheres of zinc served as conductors. 



} 



309 9 15 

 309 18 30 

 309 39 



309 48 15 



310 8 55 



A = 33 50 45 



A = 34 48 



A = 34 21 22 



A = 34 30 50 

 A = 34 52 45 



The observations for the position b of the prism were made 

 between the double readings which correspond to the other 

 position a. 



Two corresponding readings gave for the lines of Fraunhofer, 

 D and b, of the solar spectrum, 



I) 

 I 



A = 33 5] 40 

 A = 34 21 57 



* A circumstance which interferes with the accuracy of the measurements 

 is due to the fact that the sparks do not always spring from the same point. 

 This maj be prevented by coating the balls with a layer of wax. The first 

 spark bursts the coating, and all the succeeding ones follow in its path, 



