TRANSACTIONS OF SECTION A. 455 
4, The concentration of the ionic charge, required to give the observed cor- 
puscular inertia, can be easily calculated ; and consequently the size of the electric 
nucleus, or electron, is known. 
5. The old perception that a magnetic field is kinetic has been developed by 
Kelvin, Heaviside, FitzGerald, Hicks, and Larmor, most of whom have treated it 
as a flow along magnetic lines; though it may also, perhaps equally well, be regarded 
as a flow perpendicular to them and along the Poynting vector. The former doc- 
trine is sustained by Larmor, as in accordance with the principle of Least Action, 
and with the absolutely stationary character of the ether as a whole; the latter 
view appears to be more consistent with the theories of J. J. Thomson. 
6. A charge in motion is well known to be surrounded by a magnetic field ; 
and the energy of the motion can be expressed in terms of the energy of this con- 
comitant field,—which again must be accounted as the kinetic energy of ethereous 
flow. 
7. Putting these things together, and considering the ether as essentially in- 
compressible—on the strength of the Cavendish electric experiment, the facts of 
gravitation, and the general idea of a connecting continuous medium—the author 
reckons that to deal with the ether dynamically it must be treated as having a 
density of the order 10! grammes per cubic centimetre. 
8. The ether is perfectly penetrable by matter without resistance ; the absence 
of friction being specially tested by my experiment of the revolving steel discs ; 
and particles can move through it at nearly the velocity of light, as shown by 
Rutherford. Consequently reaction between ether and matter is an inertia term, 
and not a viscosity term. It behaves therefore like a perfect Huid—a perfect 
liquid of enormous density and zero viscosity. 
9. The existence of transverse waves in the interior of a fluid can only be 
explained on gyrostatic principles, z.c., in terms of kinetic or rotational elasticity. 
And the internal circulatory speed of the intrinsic motion of such a fluid must be 
comparable with the velocity with which such waves are transmitted. 
10. Putting these things together, it follows that the intrinsic or constitutional 
vortex energy of the ether must be of the order 10°° ergs per cubic centimetre. 
Conclusion.—Thus every cubic millimetre of the universal ether of space must 
possess the equivalent of a thousand tons, and every part of it must be squirming 
internally with the velocity of light. 
5. An Electrical Experiment for illustrating the Two Modes of Condensation 
of Moisture on Solid Surfaces. By Professor F. T. Trouton, F.2.S. 
Experiment has shown, what might perhaps have been anticipated from theo- 
retical considerations, that there are two possible modes in which condensed 
water vapour can exist on solid surfaces and be in equilibrium with a given 
vapour pressure. 
After which of these modes condensation will take place on bringing a surface 
into a moist atmosphere depends on its previous history. Ifthe surface has been 
dried at a high temperature, with the aid of phosphorus pentoxide, the amount of 
moisture is relatively small, and is said to be of the a type; but if the drying has 
been effected at only ordinary temperatures, there is considerably greater conden- 
sation, called of the b type. ‘This is attributed to there being in the latter case 
still some of the liquid on the surface, affording examples of nuclei for liquid con- 
densation of the 6 type, while in the former case the condensation is more ana- 
logous to the supersaturated state, which can occur when a vapour is compressed 
along an isothermal in the absence of the nuclei necessary for condensation. 
When a completely dried surface of glass is placed in an atmosphere of 
which the moisture is gradually increased from zero, the course of events is as 
follows: At first very little moisture condenses compared with that which takes 
place if the drying has been incomplete, but on reaching a certain critical vapour 
pressure the condensation is very rapid, and is now of the 6 type. 
The electrical conductivity of these two types of condensed surface layers is 
