318 Prof. D. B. Brace on Double Refraction in 
of the ether, of electric and magnetic forces, is certainly 
plausible enough to warrant further examinations and ex- 
tension experimentally. That the intermolecular forces are 
not altered by factors many times less than those obtained 
by Rayleigh, is found to be the case in the media used. 
Haperiments with Water. 
Two arrangements suggest themselves: the one, a system 
rotating about a vertical axis, the other a similar system 
rotating about a horizontal axis so as to shift the plane of 
polarization from a position at 45° to the earth’s orbital 
motion through an angle of 90°. In the matter of simplicity, 
sensibility, and stability the latter method would be prefer- 
able. However, the first arrangement was selected for the 
co) 
purpose of utilizing the same mounting for other experi- 
ments. A heavy beam was pivoted between the floor and 
ceiling so as to carry a trough with its horizontal axis inter- 
secting the pivotal axis. This system could be rotated 
continuously so as to bring it into any desired position. This 
trough was 413 ems. long, 15 cms. wide, and 27 ems. deep 
on the inside, and built up of 5 cms. planking in order to 
give sufficient stability to the polarizing and mirror systems 
which it carried. 
In order to obtain sufficient intensity through the total 
column, the 2856 cms. of water used, sunlight was so thrown 
into the trough as to keep its path the same whatever its 
position. The lens 1 (fig. 1) of about 2 m. focus converged 
the sun’s rays, from a carefully adjusted heliostat, within the 
nicol 4, after reflexion from 2 and 3. The diverging beam 
was then successively reflected from mirrors 5, 6, and 7 upon 
the concave mirror 8. The radius of curvature of this latter was 
about 15 m., and it was mounted, as were the other mirrors, 
upon brass plates containing adjusting-screws fastened to the 
ends of the trough. The axis of the reflected cone was dis- 
placed in a horizontal plane, so that the return ray passed 
through the analysing system 9-11 placed to one side of the 
polarizer. The lens 12 converged the light, which would 
otherwise have come to a focus at a distance of about 2 m. 
beyond, to the eye 15 at a distance of 25 cms. from 9. Thus 
the eye could observe 9 directly or by means of the tele- 
scope 14. Both the heliostat-mirror and the lens 1 were 
diaphragmed down so that the aperture of the cone of 
rays was slightly less than that of the mirror 8 whose aper- 
ture was about 15 cms. This prevented diffused light from 
the mirror and the water reaching the nicol 11 to any serious 
extent, and also aided in the adjustments of the mirrors 
so as to keep the rays fixed when the trough was rotated. 
