{ 595 ) 
16. If a Fresnel rhomb combined with a calespar rhomb is intro¬ 
duced in the beam, one of the components of the quartet also entirely 
disappears. At an angle of 60° this was only the case with the 
sextet. (Plate II, Fig. ll). 
17. Observations at & = 39°. 
The elliptic polarisation tested by means of the ealcspar rhomb is 
very marked, even with dilute vapour (Plate II, Fig.12, Plate III, Fig.13). 
The inner components of the quartet are now decidedly less intense 
than the outer ones. 
Plate til, Fig. 13 especially shows the smaller intensity of the 
components of Dj in the lowest stripe. Indeed, they are unmistakably 
thinner than those in the upmost stripe. 
18. According as the angle between the ray and the lines of force 
is diminished, the intensity of the field must diminish at the same 
time. In order to make it possible for the rays to traverse the field 
under smaller angles the vertex semiangle of the cones must deviate 
more and more from the theoretical optimum of nearly 55°. 
The decrease of the magnetic separation is clearly shown in our 
photographs. . 
We intend to communicate on another occasion experiments under 
smaller angles ft and to enter upon some details concerning the case 
in which the components of the triplet are not neatly separated. 
Some measurements of the ellipticity of the components will also be 
given. On the present occasion we only intended to give a general 
survey of the inverse effect, illustrating it by some particular cases. 
19. Types of separation in spot and laboratory. 
In one direction we shall now enter upon some more details. The 
magnetic separation of lines in a non-uniform field has been treated 
on a former occasion. *) The results then obtained and our present 
observations may be of some interest in connection with certain 
phenomena observed by Hale. We intend to return to this subject. 
Presently it seems interesting to allude to Mitcbell’s descriptions of 
the various types of spot lines as indicated in the diagram published 
in the Transactions of the International Solar Union*). 
Our Fig. 14, Plate III has been copied from this source. The 
types 5, 6, 7, and 10 of the Figure are yery characteristic. Type 9 
perhaps falls under the type of lines invisible without Nicol mentioned 
’) Zeeman. These Proceedings, April 1906, November 1907. 
2 ) Transactions Intern. Union Solar Research, p. 199 etc. 1908. 
40 
Proceedings Royal Acad. Amsterdam. Voi. XII. 
