240
XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
1
same as in a Thomson galvanometer.
In all the following experiments it was
made strongly astatic by external mag-
nets; this, with the air-damping, made
it dead-beat, and in all other respects
its behaviour was most satisfactory.
The tube was now brought as near as
possible to the maguet, first in such a
position that the magnet would indicate
a force tangential to the tube, then
radial, and lastly, parallel to the tube.
But there was never any deflection,-
none amounting to even one-tenth of a
scale-division in the telescope. The
strength of the current was from 100
to zoo Daniell/S.U. By using a second
anode the same current could be made
to traverse the length of the tube; it
then produced deflections of thirty to
forty scale-divisions. Similar deflections
were obtained when the first anode was
retained and portions of the circuit
outside the tube were brought within a
few centimetres of the magnet. It was
thus proved that, if there was any
specific action of the cathode rays upon
the magnet, this could not amount to
300 part of the effect produced by the
cathode rays as current-carriers.
In the principal experiments the
discharge was investigated in an air-
space of the form of a flat parallel-
epipedon, 12 cm. long, 12 cm. broad,
and 1 cm. deep. The case enclosing it
is shown in Fig. 30. It was made of
a strong brass casting, which formed
the side walls and framing, and of two
sheets of plate-glass 4 to 5 mm. thick,
applied air-tight to this frame.
The
plates sustained safely the powerful pres-
FIG. 30.