236- . Dr. P. Zeeman on the Influence of Magnetism 



intensities of the magnetization. Further inquiry must also 

 decide as to how far the strong magnetic forces existing 

 according to some at the surface of the sun may change its 

 spectrum. 



The experiments described have been made in the Physical 

 Laboratory at Leyden, to the Director of which, Prof. Kamer- 

 lingh Onnes, I am under great obligations for continuous 

 interest in the present subject. 



Amsterdam, Jan. 1897. 



Appendix. 



Since the publication of my original paper in the Proceed- 

 ings of the Academy at Amsterdam, and while the present 

 paper was in the press, I have become acquainted with two 

 attempts, till now unknown to me, in the same direction, and 

 also with the original account of Faraday's experiment referred 

 to in § 1. The last is to be found in Faraday's ' Life ' by Dr. 

 Bence Jones, vol. ii. p. 449 (1870), and as it is extremely 

 remarkable I will reprint it here : — 



" 1862 was the last year of experimental research. Stein- 

 heirs apparatus for producing the spectrum of different sub- 

 stances gave a new method by which the action of magnetic 

 poles upon light could be tried. In January he made himself 

 familiar with the apparatus, and then he tried the action of 

 the great magnet on the spectrum of chloride of sodium, 

 chloride of barium, chloride of strontium, and chloride of 

 lithium." 



On March 12 he writes: — "Apparatus as on last day 

 (January 28), but only ten pairs of voltaic battery for the 

 electromagnet. 



" The colourless gas-flame ascended between the poles of 

 the magnet, and the salts of sodium, lithium, &c. were used 

 to give colour. A Nicol's polarizer was placed just before 

 the intense magnetic field, and an analyser at the other ex- 

 treme of the apparatus. Then the electromagnet was made, 

 and unmade, but not the slightest trace of effect on or change 

 in the lines in the spectrum was observed in any position of 

 polarizer or analyser. 



" Two other pierced poles were adjusted at the magnet, the 

 coloured flame established between them, and only that ray 

 taken up by the optic apparatus which came to it along 

 the axis of the poles, i. e. in the magnetic axis, or line of 

 magnetic force. Then the electromagnet was excited and 

 rendered neutral, but not the slightest effect on the polarized 

 or unpolarized ray was observed." 



