930 REPORT— 1885. 
further, that in a crystal the light vibrations are normal to the ray, not to the 
wave normal, as was pointed out by Boussinesq, and referred to by Ketteler in 
some of his papers. 
7. Exhibition of a Mechanical Model illustrating some properties of the 
Ether. By G. F. Firzcerarp, F.B.S. 
8. On the Constitution of the Luminiferous Ether on the Vortex Atom 
Theory. By Professor W. M. Hicks, M.A., F.B.S. 
The simple incompressible fluid necessary on the vortex atom theory is quite 
incapable of transmitting vibrations similar to those of light. The author has 
therefore considered the possibility of transmitting waves through a medium . 
which consists of this fluid modified so as to contain small vortex rings closely 
packed together. The rings are supposed composed of the same material as the 
rest of the fluid, to be very small compared with the wave length, and at distances 
from one another also small compared with the wave length. Their motion of 
translation is also taken to be so comparatively slow that very many waves can 
pass over any one before it has much changed its position. Such a medium would 
probably act as a fluid for larger motions. 
The vibration in the wave front may be (1) swinging, such as a ring oscillating 
on a diameter, (2) transversal vibrations of the ring, (3) vibrations normal to the 
plane of the rings, (4) apertural vibrations. Of these (3) seems to be impossible. 
If + be the radius of the rings, 7 the distances of their planes, » their cyclic 
constant, and v the velocity of translation, the author found 
for : 
we 2t() 
hp [r\? 
oe4 
whilst for (4) in case of rings arranged parallel to a wave front, 
ye ay 
(? + 4r?)3 
for 
9. On an improved Apparatus for Christiansen’s Experiment.’ 
By Lord Rayueieu, D.O.L., LL.D., F.R.S. 
10. Optical Comparison of Methods for observing small Rotations.? 
By Lord Ray.eicu, D.C.L., DL.D., F.R.S. 
11. On the Accuracy of Focus necessary for sensibly athe Definition. 
By Lord Rayteicu, D.C.L., LL.D., F. 
12. On Electro-Optice Action of a charged Franklin’s Plate.‘ 
By J. Kerr, LL.D. 
The experiments described in this paper were carried out by the author in 
1882, and he has now made them known in view of certain statements made by 
M. Wiedemann in his ‘ Die Lehre von der Electricitit,’ vol. ii.; particularly where 
1 Published in the Phil. Mag., Oct, 1885. 2 Thid. 
> Ibid. 4 Thid. 
