The greatest difference in the different columns is shown by group 
IV. Here the different numbers 0.22, 0.40, 0.68, 0.93 point to the 
fact that the lines of this group (to which belong all so-calied 
“enhanced lines”) are sensitive in very different degrees to the 
different ways in which the pressure-effect has been determined. As 
to the Zreman-effect these lines (except that one of them does not 
show a magnetic decomposition) ‘do not show any particularity. 
Comparing the columns with each other, we see that the column 
Z ; ZE 
5 Berees best with the column of the mean DE Also for the other 
2 
columns there may be found partial correspondences. 
Though there is not much observation-material, we see from the 
above that a division into groups can still teach something abont 
the connection between Zenman-effect and pressure-effect. An investi- 
gation, as King') made for the spectra Fe, Cr and 7% which has 
given a great number of observations, could not be carried out here. 
Perhaps that later sull more observations on the pressure-effect and 
“also on the Zrwmar-effect will be published which would give us 
the opportunity to carry out this investigation more completely. 
Physics. — “The Theory of the Brownian Movement”. By Prof. 
J. D. van per Waars Jr. and Miss Aupa SNRTHLAGE. (Com- 
municated by Prof. J. D. van per WAALS). 
(Communicated in the meeting of January 29, 1916). 
§ Lt. In different ways it has been tried to derive a formula for 
the deviation which a suspended particle will present on an average 
in a definite time in consequence of the Brownian movement. In most 
of these derivations the supposition is introduced that the particle 
when moving experiences a friction, i.e. that a force acts on the 
particle which can be represented by — pv, when v represents the 
velocity of the particle and p a positive constant. As far as is known 
to us the first of the two formulae derived by Von SMOLUCHOWSKI*) 
is the only one where this supposition has not been made use of; 
in the derivation of this formula kinetic considerations have been 
exclusively used. 
The formula derived in this way, which we shall call Sm. I, 
deviates pretty considerably from the second *) derived by Von 
Nella) tee 
2) Von SMOLUCHOWSKI. Ann. der Phys. 21. p. 769. Ann. 1906. 
5) Von SmoLucHOowSsKI! Le. p. 773. 
