TRANSACTIONS OF SECTION A. 701, 
equipped for investigating the secrets of nature than if, like the White Knight of 
‘Alice in Wonderland,’ he commences his career knowing how. to, measure 
or weigh every physical quantity under the sun, but with little desire or 
enthusiasm to have anything to do with any of them. Even for those students 
who intend to devote themselves to other pursuits than physical investigation, the 
benefits derived from original investigation as a means of general education can 
hardly be over-estimated ; the necessity it entails of independent thought, perseve- 
yance in overcoming difficulties, and the weighing of evidence gives it an educational 
value which can hardly be rivalled. We have to congratulate ourselves that 
through the munificence of Mr. Ludwig Mond, in providing and endowing a labora- 
tory for research, the opportunities for pursuing original investigations in this country 
have been greatly increased. 
The discovery at the end of last year by Professor Réntgen of a new kind of 
radiation from a highly exhausted tube through which an electric discharge is 
passing has aroused an amount of interest unprecedented in the history of physical 
science. The effects produced inside such a tube by the cathode rays, the 
bright phosphorescence of the glass, the shadows thrown by opaque objects, the 
deflection of the rays by a magnet, have, thanks to the researches of Crookes and 
Goldstein, long been familiar to us, but it is only recently that the remarkable 
effects which occur outside such a tube have been discovered. In 1893 Lenard, 
using a tube provided with a window made of a very thin plate of aluminium, 
found that a screen impregnated with a solution of a phosphorescent. substance 
became luminous if placed outside the tube in the prolongation of the line from the 
cathode through the aluminium window. He also found that photographic plates 
laced outside the tube in this line were affected, and electrified bodies were discharged ; 
e also obtained by these rays photographs through plates of aluminium or quartz. 
He found that the rays were affected by a magnet, and regarded them as the pro- 
longations of the cathode rays. This discovery was at the end of last year followed 
by that of Rontgen, who found that the region round the discharge tube is traversed 
by rays which affect a photographic plate after passing through substances 
such as aluminium or cardboard, which are opaque to ordinary light; which pase 
from one substance to another, without any refraction, and with but little regular 
reflection ; and which are not affected by a magnet. We may, I think, for the 
purposes of discussion, conveniently divide the rays occurring in or near a vacuum 
tube traversed by an electric current into three classes, without thereby implying 
that they are necessarily distinctly different in physical character. We have (1) 
the cathode rays inside the tube, which are deflected by a magnet ; (2) the Lenard 
rays outside the tube, which are also deflected by a magnet; and (3) the Réntgen 
rays, which are not, as far as is known, deflected by a magnet. Two views are held 
as to the nature of the cathode rays; one view is, that they are particles of gas 
carrying charges of negative electricity, and moving with great velocities which 
they have acquired as they travelled through the intense electric field which exists 
in the neighbourhood of the negative electrode. ‘The phosphorescence of the glass 
is on this view produced by the impact of these rapidly moving charged particles, 
though whether it is produced by the mechanical violence of the impact, or whether 
it is due to an electro-magnetic impulse produced by the sudden reversal of the 
velocity of the negatively charged particle—whether, in fact, it is due to mechanical 
or electrical causes, is an open question. This view of the constitution of the 
cathode rays explains in a simple way the deflection of those rays in a magnetic 
field, and it has lately received strong confirmation from the results of an experiment 
made by Perrin. Perrin placed inside the exhausted tube a cylindrical metal 
vessel with a small hole in it, and connected this cylinder with the leaves of a gold- 
leaf electroscope. The cathode rays could, by means of a magnet, be guided so as 
either to pass into the cylinder through the aperture, or turned quite away from it. 
Perrin found that when the cathode rays passed into the cylinder the gold leaf of 
the electroscope diverged, and had a negative charge, showing that the bundle of 
eathode rays enclosed by the cylinder had a charge of negative electricity. Crookes 
had many years ago exposed a disc connected with a gold-leaf electroscope to -the 
- bombardment of the cathode rays, and found that the disc received a slight. positive 
