875 
finds a separation proportional with 4 %€, WarBere however a 
broadening proportional with p?2°€, where p denotes the number of 
the series. The formulae of GARBAssO, GEHRCKE and Bonr *) differ 
from that of Warsure in so far only as, besides other numerical 
factors, they contain p*.€ as a parameter. The simultaneous influence 
of a magnetic and an electric field was treated both theoretically and 
experimentally by ZEEMAN, Stark, GARBASSO and GEHRCKE °). 
Luminescent vapours always more or less cause a migration of 
electricity which in the experiments of Stark e.g. amounted to several 
milliamperes. It seemed to me interesting to examine the influence 
of a purely dielectric displacement. As Zunman already pointed out (loc. 
cit.) for this purpose we must consider an insulating, selectively 
absorbing crystal. Among the series of substances formerly tested 
ruby will be found a very good material for such experiments *). 
It is not hygroscopic, it insulates extremely well and has an 
ordinary index of refraction n,=—1,769 (for 2 = 589 wy), and 
Ns = 3,13. Considering the analogy with quartz we may expect 
the dielectric constant to be much larger still. In connection with 
this research SELENny1*) already investigated in the Bosscna-laboratory 
the influence of an elastic deformation on the absorption lines of 
ruby. For a pressure of 150 kg/mm’? however he could not detect 
an appreciable effect, at least no more than 0,02 uu. 
The electrostatic experiment had to be delayed several years by 
the difficulty of obtaining artificial rubies of sufficient size, because 
of a monopolistic tendency in their preparation. Only recently I was 
kindly furnished with sufficient material. From this two disks 
“were cut, about 3 mm thick, one 1 and one || the crystal axis: 
By means of sealing wax these were fixed within ebonite plates 
of the same thickness. Unsymmetrical contraction by sudden cooling 
or high electrostatic tension (during a short time) did not appreciably 
injure these slides. To both sides of the dielectric plates small brass 
disks were fixed. In the middle of these a slit was made so that 
an eventual longitudinal effect might be observed. Extremely thin 
tubes of German silver fitted in glass tubes connected the brass 
1) A. GarBasso, Phys. Ztschr. 15 pp. 123, 310, 1914, B. Geurcxe, Phys. Ztschr. 15 
pp. 123, 198, 344, 839, 1914; Verh. D. Phys. Ges. 16 p. 431, 1914. N. Bour, 
Phil. Mag. (6) 27 p. 506, 1914. 
*) P. ZEEMAN, These proceedings, 14 p. 2, 1911. J. Stark, Verh. D. Phys. Ges. 16 
p. 327, 1914. A. Garsasso, Phys. Ztschr. 15 p. 729, 1914, E. Geurcxs, Phys. 
Ztschr. 15 p. 839, 1914. 
5) H. pu Bors and G. J. Erras, These proceedings, 10 pp. 578, 734, 839, 
1908 ; Ann. d. Phys. 27 p. 233, 1908; 35 p. 617, 1911; 45 p. 1160, 1914. 
4). P. SeLÉNyi, Verh. D. Phys. Ges. 15 p. 290, 1913. 
58* 
