1902.] 



On the Energy of Magnetisation. 



229 



The entire chromosphere is supposed to consist of innumerable 

 small eruptions or jets of highly-heated gases similar to the so-called 

 " metallic " prominences, which are only the more pronounced mani- 

 festations of the same eruptive agencies. 



Evidence for this is found in the characteristic features of the 

 chromosphere, and in the detailed structure of many of the Fraun- 

 hofer lines, which show wide emission lines underlying the narrow 

 absorption lines. These ill-defined bright lines in the normal solar 

 spectrum are distinctly displaced towards the violet, indicating a strong 

 uprush of the hotter gases, whilst the narrow absorption lines are 

 almost in their normal positions, and appear to indicate a slow and 

 uniform descent of the absorbing gases. 



The final conclusion is that the flash spectrum represents the 

 emission of both ascending and descending gases, whilst the Fraunhcf er 

 spectrum represents the absorption of the descending gases only. 



" On the Electrodynamic and Thermal Eelations of Energy of 

 Magnetisation." By J. Larmor, M.A., D.Sc, Sec. E.S. Ee- 

 ceived January 2, — Eead January 22, 1903. 



1. There appears to be still some uncertainty as to the principles on 

 which the energy of magnetised iron is to be estimated, and the 

 extent to which that energy is electrodynamically effective. The 

 following considerations are submitted as a contribution towards 

 definite theoretical views. 



The electrokinetic energy of a system of electric currents i v c 2 , . . ., 

 flowing in complete linear circuits in free aether, is known to be 



i(tiN 1 + t 2 N 2 + . . 



wherein Ni is the number of tubes of the magnetic force (a, /?, y) that 

 thread the circuit ti, and is thus equal to J (la, + mp + ny)dS ex- 

 tended over any barrier surface S which blocks that circuit, (a, /5, y) 

 being circuital (i.e., a stream vector) so that all such barriers give the 

 same result. As under steady circumstances (a, j3, y) is also derivable 

 from a magnetic potential V, which has a cyclic constant 4~t with 

 regard to each current, this energy assumes the form 



1' r / 7 8V oY SV\ TO 



in which the integrals are now extended over both faces of each 



