238 Influence of Magnetism, on the Nature of Light. 



of the emitted light. The results obtained by M. Fievez 

 merit careful attention and consideration. He has observed 

 with a flame in a magnetic field not only widening but 

 reversal and double reversal of the lines of the spectrum, the 

 lines at the same time becoming more brilliant. Unfortu- 

 nately quantitative details are not given. The facts observed 

 in some cases by Fievez are qualitatively not in accordance 

 with my observations or what is to be deduced from my 

 results. Hence even in the cases where the results are 

 qualitatively in accordance, the question remains whether 

 Fievez has observed the same phenomenon. The field used 

 by Fievez seems to have been more intense than the one 

 I had at my disposal. Is it possible perhaps to account in this 

 manner for the " double renversement (c'est-a-dire Papparition 

 d'une raie brillante au millieu de la raie noire elargie) " ? 

 I think the answer must be in the negative. For, arguing 

 from § 19, a line must widen, or else, the field being very 

 intense, become a triplet. We cannot but understand from 

 Fievez's description of the experiment that the light was 

 emitted perpendicular to the lines of force. Now the double 

 reversed line of Fievez is not the triplet to be expected from 

 theory, for it is expressly stated by Fievez that the line expe- 

 rimented upon is not the simple line of the spectrum, but one 

 previously widened and reversed (by some agency independent 

 of magnetism). By the action of magnetism a brilliant line in 

 the centre of the black line appears. Hence perhaps one may 

 interpret the case of double reversal as a direct action of mag- 

 netism, but then only as a doubling of the absorption -line and 

 not as a division of the original line into three parts. As the 

 application of Lorentz's theory given in § 18 is confessedly 

 only a very first sketch, further theoretical and experimental 

 evidence is wanted before we are able to decide whether in 

 the experiment of Fievez a specific action of magnetism on 

 light or perturbing circumstances have been prevalent. 

 Indeed one may make the same objection to M. Fievez's ex- 

 periment as I myself have made to my own analogous experi- 

 ment in § 6. 



The whole of the phenomena observed by Fievez can 

 readily be attributed to a change of temperature by the well- 

 known actions of the field upon the flame (change in its 

 direction or outline, magnetic convection, &c.) ; and the last 

 sentence of his paper states that "les phenomenes qui se 

 manifestent sous Faction du magnetisme sont identiquement 

 les memes que ceux produits par une elevation de tempera- 

 ture."" The negative result obtained by Fievez with absorp- 

 tion-spectra would without further consideration (as in § 12) 



