( *84 ) 
This expeeiment was started on July 14 th 1908; the incisions were 
ready and the plates were pushed in at 9.30 a.m. At 10 a.m. the 
leaves were already drooping and they remained so throughout 
the day. 
In the course of the five following days, in cool dry weather, the 
leaves gradually recovered. On the 7 th day of the experiment the 
foliage began to wither from the top downwards; many yellow leaves 
also appeared in the crown. In all these days the temperature had 
not risen above 18° in the neighbourhood of the tree. On the 9 th day 
the temperature rose in the afternoon to more than 26°, and probably 
as a result of this the number of yellow leaves now increased 
rapidly. Those leaves which had remained green also began to droop 
again. The tops of the branches in the upper part of the crown 
withered completely. 
The 3 following days were warm and sunny with temperature 
maxima of 27° and 28°. Most of the leaves now fell olf, while in 
the upper half of the crown the foliage withered completely. 
After this time cooler weather supervened and the few remaining 
green leaves recovered and remained in good condition until the 
autumn. 
That the tree had not suffered greatly however from the incisions, 
was shown in the following summer, for then the foKage developed 
as well as before the experiment, and remained fresh throughout 
the entire season. 
Wageningen, Dec. 13 th 1909. 
Physics. — “ The magnetic separation of absorption lines in connexion 
with Sun-spot spectra .” (I). By Prof. P. Zeeman and Dr. B. 
WlNAWER. 
1. As a consequence of the intimate connexion between emission 
and absorption, there exists closely corresponding to the magnetic 
separation of emission lines, a magnetic division of absorption lines. 
The dark lines which appear in a continuous spectrum, if a beam 
of white light traverses an absorbing flame, are divided and pola¬ 
rized under the influence of magnetic forces in exactly the same way 
as the emission lines. This correspondence between emission and 
absorption was shown to exist already in some of the first experi¬ 
ments on the subject by one of the present authors. Our knowledge 
of emission spectra under magnetic influence has since been extended 
considerably. The experimental study however of the inverse effect 
Le. the magnetic division of absorption lines has less advanced. 
