302 
3. Observations. The different intensities of the field were always 
determined by measuring the resolutions which were caused by them 
for Zn 4680, in which the degree of resolution of this line was 
compared with that obtained with the well-known absolute measure- 
ments of Genin, Weiss and Corron'), and Forrar ®). As standard 
aA 
value for ane halen I took the mean of the values obtained by them, 
} 
viz. 9,376. I mostly worked with fields that lay in the neighbourhood 
of 30000 Gauss. 
For tin and lead the electrodes were flexible strips of these metals, 
which were stretched cross-wise over the pole tops. For tin the 
spark was still cooled by blowing with a Féhn, because otherwise the 
electrodes were melted through too quickly, and the discharge passed 
into a continuous one. This method was discarded for lead, because 
with the Féhn there would often be a hitch, and an auxiliary spark 
was inserted in the secondary circuit in series with the illumi- 
nating spark. By regulating the distance of this auxiliary spark, we 
have much better control over the action of the illuminating spark. 
The electrodes of the auxiliary spark must not oxidise, however, 
because then we get there a more continuous discharge, whereas 
the very function of the auxiliary spark is to obviate this drawback, 
which is met with for the illuminating spark, and is not to be avoided 
there; it has, therefore, to ensure an interrupted discharge. For this 
purpose the bulbs of brass, of which the auxiliary spark consisted, 
were coated with platinum hoods. The strips of lead were kept 
tightly stretched over the pole tops, as otherwise they are apt to bend 
over towards each other, thus rendering the spark length too small. 
No flexible bands could be made of antimony on account of the 
brittleness of this metal; I therefore used small flat rods of this 
metal as electrodes, which were clasped in a spark stand of brass. 
An advantage of this metal is that it has a pretty high melting-point, 
and that therefore the electrodes do not so quickly melt through. 
I have only used Bismuth as elecirode as alloy with antimony (60 
percentages by weight of bismuth) else it combined the drawbacks 
of tin and lead that it melted soon, and that of antimony that it 
was brittle. In the alloy the first drawback was eliminated, and it 
could further be used as antimony. 
I must state further that in the tables in which ScHiPPers *) records 
1) P, ZEEMAN. Researches in Magneto-optics. Mac Millan and Co, London, 1913, 
p. 67. Deutsche Uebersetzung, Leipzig, J A. BARTH, 1914. 
2) R. Forrar. Recherches de magneto-optique. Thèse, Paris, 1914. 
8) H. Scurppers, Messungen am Antimonspectrum. Zs. f. Wiss. Phot., 11, 
235, 241. 
