Jan., 1892. 
THE BRITISH ASSOCIATION AT CARDIFF. 
17 
that many floating leaves are much divided, apparently to 
facilitate the drainage, and that some are clothed with hairs, 
in order to repel water from their surfaces. Altogether, I think 
the subject is well worth the attention of botanical students. 
The second lecture was delivered by Professor Rucker, 
and was a splendid example of an experimental lecture. His 
subject was that of “ Electric Stress.’’ By this is meant the 
action of electrified bodies upon interposed non-conducting 
substances. Faraday long ago showed that a non-conductor 
does not play a merely passive part, when placed between two 
conducting bodies, one of which is electrified ; but I never 
saw the action made so evident as it was in Professor 
Rucker’s lecture. If the two terminals from an electrical 
machine be placed in a shallow glass vessel containing ether, 
and sulphide of antimony be sprinkled in, when the machine 
is worked the powder will arrange itself between the poles in 
a manner similar to the behaviour of iron filings between two 
magnetic poles, with this difference that the particles tend to 
gather around the + pole. To shew the action upon the 
dielectric, carbonic disulphide is used with polarized light. 
In its normal condition CS 2 transmits polarized light without 
change ; but, if it be between two differently electrified plates, 
the beam of light, if its plane of polarization were inclined 
to the plane of the plates, becomes partially depolarized. 
If it be then passed between another pair of electrified 
plates, at right angles to the first, the action is reversed, 
unless the one pair have charges of the same kind. In 
fact, the liquid under the influence of electricity behaves 
just like a plate under mechanical pressure : we have 
accomplished the, at first sight, impossible task of squeezing 
a liquid in one direction and not in another. A variety 
of experiments were shewn amplifying this principle. If 
the action was sufficiently intense, colour was shewn to be 
produced. This when analysed by the prism exhibited a 
spectrum with a dark band in it, which moved along it, 
according to the amount of electric stress. Even after the 
band had moved off the visible spectrum at the red end, 
it was shewn to be present in the ultra-red region by 
means of Mr. Boys’s radio-micrometer. 
There were two conversaziones given by the local com¬ 
mittee. Exhibits of scientific objects were not very numer¬ 
ous, but I note the following. There was a lantern 
exhibition of views from Languedoc in S. France, which 
shewed scenes strikingly resembling the canons of Colorado. 
The district is so remote from the ordinary run of tourists 
that it has remained comparatively unknown. There was 
also an exhibit by Professor Copeland of a model to shew a 
