is derived and the values e/ep have been caleulated finally, which 
values determine the dispersion of the magnetic gases. These different 
numbers are combined in table 2, while fig. 8 shows graphically 
the values of o/ep. 
TABLE 2, 
4 | 4 | Q | elen} 4 A e | o/ep 
112 490 |0.02748 | 2.003 | 214.5] 575 |0.01455 | 4.061 
116 131 2653 | 1.835 | 216 579 | 4425 | 1.039 
194 AAG 482 | 1 810 919.5 583 1402 1.092 
130.5 | 458 9358 | 1.719 [589] | [1372]} 4 000 
165 5LO 1865 | 1.360 EN 599 tara be 0 971 
166 59, 185% 1301 2390 G04 | TOU |e Oe Gas 
476.5 | 597 1744 | 1.971 | 237 60% 1299 | 0.947 
184.5 | “536 1668 | 4.216 | 49.5 | 616 1234 | 0.899 
189.5 | 543 | ac lass | 950 | car | 42931 | 0.898 
196.5 | 554 1566 | 4.142 | 273 | 643 1127 | 0.822 
196 555 1570 | 1.445 | 283 659 1089 | 0.794% 
In this calculation the rotation in the glass plates has been neglected. 
A simple calculation shows us that this is permissible ; for it should 
be remembered that this is done both for the measurements with 
methyl chloride and with water. 
As the result of this research I find that the magnetic rotation 
constant for liquid methyl chloride under atmospheric pressure for 
sodium light is 001872, and that the rotation dispersion is normal, 
deviating little from that with gases and with water. 
The research will be continued with other gases. 
Physics. — “Diffraction of Röntgen-Rays”” By Prof. H.- Haga 
and Dr. CG. H. Winxp; second communication. 
In the March meeting 1899 we stated as the result of our expe- 
riments that Réntgen-rays show diffraction; with these experiments 
the rays passing through a narrow slit first fell on a second wedge- 
shaped slit, then on a photographic plate. The image proved not 
