( 90 ) 



It is remarkable that the liquid-curve in fig. 5 should differ so 

 little from the straight line. So it seems that for these mixtures 

 at the chosen temperature the vapour-pressure of the liquid-phase 

 may be represented with near approximation by: 



P = Pi (l-x) + P^x 



in which Pj and P^ represent the vapour-pressures of the compo- 

 nents. If we compare this with the formula given by van der Waals ^), 

 it appears that the exponents in the latter differ little from zero. 



Physics. — ■ ^^Considerations concerning the Influence of a Magnetic 

 Field on the Radiation of Light.'" By Prof. II. A. Lorentz. 



§ 1. The assumption that every molecule of a source of light contains 

 a single movable ion, which cau be displaced in all directions from 

 its position of equilibrium and is always driven back to that position 

 by the same force, proportional to the displacement, leads to the 

 elementary theory of the phenomenon disciovered by Dr. Zeeman. 

 Viewed across the lines of force, a single spectral line must, by the 

 action of the field, be tripled, and viewed along the lines of force, 

 be doubled ; besides, the components of the triplets and doublets 

 must be polarised in a well known manner. 



Whilst the first observations of Zeeman were consistent with this 

 theory, and he soon could confirm the theoretical predictions by the 

 observation of distinct triplets and doublets, yet it has become ap- 

 parent that the case is often less simple. Cornu proved, that f. i. 

 in the case of one of the sodium lines, viewed across the lines of 

 force, the central component of the triplet is doubled, so that in 

 reality a quadruplet is seen. Michelson and Th. Preston observed in 

 many cases not only a far more complicated structure of the central 

 component, but a similar structure of the outer components of the 

 triplet. According to these observations, the word „triplet" is 

 hardly applicable, though there is always an important difference 

 between the central part of the appearance in the spectrum (the two 

 central lines, f. i. of Cornu's quadruplet) and the outer parts; the 

 first is plane polarised, the plane of polarisation being perpendicular 

 to the lines of force, whcireas in the right and left part the plane 

 of polarization is parallel to the lines of force. 



§ 2. The facts mentioned evidently make it necessary to replace 



') Y. L). Wa.vls, Vei-slag- Kou. Aknd, May 28 "'Jl p. 410. 



