TRANSACTIONS OF SECTION A, 467 
If the sphere were cut from some 7'ea/ isotropic substance it would under these 
conditions send out electric vibrations whose directions lie exclusively in planes 
which pass through the f axis—that is, in mertdian planes, and which are con- 
nected with magnetic vibrations perpendicular to this plane. But since the sphere 
is pseudo-isotropic it also sends out rotational electric vibrations around the 7 
axis, perpendicular to the meridian planes, connected with magnetic vibrations 2 
the meridian planes. 
The presence of these circular electrical vibrations may be experimentally 
demonstrated if we surround the sphere with a flat coil of wire, placed in the 
equatorial plane and connected with a detector of sufficient sensibility. 
For a point of the equator the circular electric force has a comparatively 
simple value. Let v be the difference between the indices of refraction for sodium 
light of the two circularly polarised waves propagated within the medium, and 
« be the ordinary dielectric constant of the medium ; let \ be the wave length in 
empty space of the electric vibrations amongst which the sphere is placed, Ts/T 
the ratio of the periods of sodium light and of the electric waves employed; 
R the radius of the sphere, and Z the amplitude of the existing electric vibrations. 
Then, in an allowed approximation, the amplitude T of the circular electric force 
is given by 
bd. cee K f 
a a Ts 
Since v as well as T,/T and RjA are small, the coefficient of f is very small, 
and observations about the calculated effect may be made only in a qualitative 
way. I used a regularly formed piece of quartz, which was allowed with certain 
restrictions to be taken as a sphere of a pseudo-isotropic medium, I had Rnearly 
4 em., f= 4000 volts, A=100 m. and a coil of 200 turns. In these conditions an 
electromotive force of about 10-* volt in the coil was to be suspected. This is a 
very weak effort, which can be easily cloaked by other vibrations which affect the 
detector ; for instance, by those coming directly from the electric oscillator. 
In some cases it was possible to make the disturbing effects very small, and to 
observe an electric vibration similar to that suspected; for the most part, however, 
the results were doubtful. I shall, therefore, have to lay more stress upon the 
interesting indications of theory than upon the results of observation, 
Pe=p. 
6. Discussion on N-Rays, Opened by Dr. O. Lummrr. 
Having been asked by the Committee to open a discussion on the N-rays, I 
gave a short account of the experiments which Professor Rubens and I had carried 
out on this curious subject. We had worked hard to detect them, but had abso- 
lutely failed, both in the direction of photographic effect with the spark and of sub- 
jective observation. We made besides photometrical experiments, not previously 
carried out, which showed that, observing in the dark a faintly luminous screen 
indirectly, with a well-adapted eye, the difference of intensity must be changed 
at least 30 per cent. to give a perceptible effect. On the other hand, the change 
from direct to indirect vision increases the intensity from one to four and more, due 
a i fact that we observe directly with the cones of our retina, indirectly with 
the rods. 
But also in the case of continued indirect vision, which the N-ray observers 
maintain to be necessary, physiological processes go on in the eye which give 
great variability of the luminosity of such small phosphorescent screens, one of 
which I described under the title of the ‘Heinrich-Phenomenon.’ All our ex- 
periments, therefore, confirmed our opinion that all such effects, including the 
newest experiments of Jean Becquerel, were to be attributed to physiological 
causes. 
Mr. Butler Burke, of the Cavendish Laboratory, gave an account of his experi- 
ments with a view to obtaining evidence as to the nature of this new, and it might 
HH 2 
