The Radioactivity of Sea- Water. 385 
magnesium on encountering these at their terminations, and 
that a similar luminescence occurs at the surface which forms 
the base of the Sprays on the cathode. Should the propaga- 
tion cathode-wards of the Sprays be established, then on the 
assumption of the already existing hypothesis that the first 
layer of the cathode glow consists of carriers of positive 
electricity, we might attempt to deduce the origin of the 
other members of the canal-ray group of the Sprays. Thus, 
in order to account for the Kj-rays, we might suppose that 
during the impact of the positive Sprays on the cathode there 
occurs a partial rebound of the particles, which are then 
characterized by a strongly diminished charge, and must 
therefore in accordance with theory be much less sensitive. — 
A nearly parallel beam of Sprays arriving in a nearly 
tangential direction at the walls of a slit would suffer various, 
changes of charge, according to the distance of its individual 
rays from the cathodic walls of the slit, and would, on account 
of its variously charged particles being at various distances 
from, and hence suffering varying deflexions by the negative 
surfaces, be transformed into a more strongly conical beam, 
whose components would, in the space between the walls, 
proceed partly in a tangential, partly in oblique directions. 
The concavity, towards the neighbouring sides, of the positive 
beams which sweep across the polygonal plates would thus be 
accounted for, as well as the fact that outside the space 
between the plates the rays again proceed along straight 
lines, forming tangents to the last elements of their curvilinear 
path between the plates. The decrease of charge taking- 
place during the motion across the plates would explain why 
the canal rays emerging on the opposite side are much less 
sensitive than the Si-rays. The nebulous rays, which emerge 
in a highly divergent form, would also be accounted for. 
XXXVII. The Radioactivity of Sea-Water. By J. Joly, 
Sc.D., F.R.S., Professor of Geology and Mineralogy in the 
University of Dublin, Hon. Sec. Royal Dublin Society*. 
I AM acquainted with only one determination of the 
radium in sea-water taken directly from the ocean — 
that recorded by A. S. Eve in his paper " On the Ionization 
of the Atmosphere over the Ocean " f. Strutt had previously 
determined the radium in sea-salt {, and obtained the value 
* Communicated by the Author. In part reprinted from the Scientific 
Proc. Royal Dublin Sec. xi. No. xxii. 
t Phil. Mag. ser. 6, vol. xiii. p. 248. 
X Proc. Roy. Soc. vol. lxxviii. p. 151. 
