Physics. — ‘Researches on the Spectra of Tin, Lead, Antimony, 
and Bismuth in the Magnetic Field.” By Dr. P. A. van DER Harst. 
(Communicated by Prof. P. Zeeman). 
(Communicated in the meeting of June 28, 1919). 
To carry out the observations of which the description will follow 
here, I have made use of the grating apparatus of the Physical 
Laboratory at Amsterdam, which had been placed at my disposal 
by Prof. P. Zrrman. 
The experiments will be described more at length in my thesis 
for the doctorate, which will be published under the above title. 
1. The spectra of tin, lead, antimony, and bismuth have been 
little, if at all, studied as to, their ZEEMAN effect. The only scientist 
that made systematic observations on these elements in this respect, 
is Purvis '). As is known, his results often present, however, great 
deviations from those of others, which is chiefly owing to an error 
in the measurement of the intensity of the field. Besides, Purvis 
measures but few lines of these elements, viz. only those for which 
no longer time of exposure was required than half an hour to get 
them distinctly enough on the photographic plate to be measured. 
It seemed, therefore, desirable to me to subject the magnetic resolution 
for these elements to a closer examination. 
2. The grating apparatus has been described by Mrs. H. B. 
BILDERBEEK—VAN Mrours*®). The grating is a concave one of Rowland ; 
radius 3 m., width 8 em, 14488 lines per inch. Slit and grating are 
rigid with respect to each other, and with respect to an iron circular 
arch, on which the photographic plates are clasped, so that the 
exposure can be simultaneous in all orders. 
The width of the slit generally amounted to about 20 u, ie. 8 
1) J. E Purvis. The Influence of a very Strong Magnetic Field on the Spark 
Spectra of Lead, Tin, Antimony, Bismuth and Gold. Camb. Phil. Soc., 14, 217, 
1907; Nature, 76, 166, 1907. 
*) H. B. BitpeERBEEK—v. Meurs. Magnetische splitsing van het ultraviolette 
ijzerspectrum (A 2800—A 4500). Diss., Amsterdam, 1909. 
