[ 255 ] 



XXXII T. Doublets and Triplets in the Spectrum produced by 

 External Magnetic Forces. — (II.)* By Dr. P. ZEEMANf. 



13. Magnetic Triplet. — With the grating of § 8 and with 

 a very strong current and rightly-shaped conical poles I 

 succeeded in observing also the pure triplet (§ 5) with cad- 

 mium. Again the blue cadmium line was examined which I 

 have used for the other characteristic phenomena. The field 

 used was about 32,000 C.Gr.S. Using this strong field and 

 looking without a nicol across the lines of force the cadmium 

 line was seen tripled, i. e., broken up into three lines, separated 

 by dark spaces. The existence of this triplet demonstrates, as 

 it seems to me, irrefragably, and independently of the exami- 

 nation of the state of polarization, the magnetic nature of 

 the phenomenon. 



If now a nicol is placed in the rays with its plane of 

 polarization horizontal, then only the two outer lines of the 

 triplet are seen. A rotation of the nicol over 90° makes 

 appear the central line and quenches completely the light of the 

 outer ones. Hence the central line of the triplet emits plane- 

 polarized light, the plane of polarization being vertical ; the 

 outer lines, on the other hand, emit light polarized in a 

 horizontal plane. This result entirely confirms the considera- 

 tions of § 3 and § 5. The question of § 12 is now answered. 

 New evidence in favour of the interpretation by Lorentz's 

 theory of the magnetization of the spectral lines has been 

 obtained. 



14. Measurement of Magnetic Change. — The triplet and 

 also the " triplet a " of § 6 enable us to measure accurately 

 the magnitude of the magnetic change ; on a former occasion % 

 I have given only the result of a rough measurement in order 

 to determine the order of magnitude. Using the " triplet a " 

 I have now obtained a far more reliable value. Looking 

 across the lines of force and quenching the horizontal vibra- 

 tions by means of a nicol the vertical vibrations only emerge. 

 Using a grating there are to be seen two separate lines, con- 

 sisting of vertical vibrations. The distance between the centra 

 of these lines corresponds to the double change of the period. 

 Of course, this distance can be measured far more accurately 

 than the widening of a line. The accuracy of the measure- 

 ment by means of a micrometer eyepiece is much increased if 



* Continued from page 60. The §§ 13-17 were communicated to the 

 June meeting of the Amsterdam Academy, § 18 is now added. 

 t Communicated by the Author. 

 \ Phil. Mag. March 1897, p. 230. 



