Dispersion in Relation to the Electron Theory. 255 



The values of A x calculated from equation (9) are 



ac = 1803 



bd = 1816 MeanX 1 = 1804. 



ce = 1805 



df= 1793 



No progression is here shown, formula (9) thus repre- 

 senting the magnetic dispersion with sufficient accuracy 

 within the visible spectrum. Verdet's values for the D and 

 F lines of the solar spectrum give a value quite near to the 

 above. 



S D /£ E = -768, n = 1-6291 *> 



S P /8 B = 1-234, n = 1-6538 J Xl = ' 186L 



The value so obtained does not, however, represent an 

 actual dispersion period or position of metallic reflexion as 

 it is too small to account for the natural dispersion. The 

 mean dispersional period for the latter required by formula 

 (3) is placed by Martens at '2175, and by Flatow at -2255. 

 The formulas obtained, however, do not tit at all well in the 

 extreme ultraviolet, e. g., 



X. w(obs.) (Flatow). Diff. (Martens). Diff. (Flatow). 



•274 2-0053 --0073 +'0320 



As the errors are of opposite sign it is probable that the 

 mean band lies between the two values here given. The 

 low value obtained from the magnetic rotation shows that 

 the constant k 2 must be introduced, as in equation (10), but 

 this equation cannot be applied to calculate the longer 

 dispersional period without a more extended series of obser- 

 vations or measurements carried to a higher degree of 

 accuracy in the visible. I hope to repeat the determination 

 shortly with a more powerful electromagnet. 



Symmetrical Units. — The system of units adopted in the 

 formulse above is that in which all electrical quantities, 

 including current and resistance, are expressed in electro- 

 static units, all magnetic quantities in electromagnetic units, 

 the connexion between the two being established by the two 

 circuital relations : 



4tt dF 1TJ 



1 dB , , r 



O W = curlx - 



