i879-] 
Molecular Physics in High Vacua. 
43i 
about like a flexible wand as I move the magnet up and down. 
The action of the magnet can be understood by reference to 
this diagram (Fig. 14). The north pole gives the ray of 
molecules a spiral twist one way, and the south pole twists 
it the other way ; the two poles side by side compel the ray 
to move in a straight line up or down, along a plane at right 
angles to the plane of the magnet and a line joining its 
poles. 
Now it is of great interest to ascertain whether the law 
governing the magnetic deflection of the trajectory of the 
molecules is the same as has been found to hold good 
at a lower vacuum. The former experiment was with a very 
high vacuum. This is a tube with a low vacuum (Fig. 15). 
Fig. 15. 
On passing the induction spark it passes as a narrow 
line of violet light joining the two poles. Underneath 
I have a powerful eleCtro-magnet. I make contadl with 
the magnet, and the line of light dips in the centre to- 
wards the magnet. I reverse the poles, and the line is 
driven up to the top of the tube. Notice the difference be- 
tween the two phenomena. Here the aCtion is temporary. 
The dip takes place under the magnetic influence ; the 
line of discharge then rises, and pursues its path to the 
positive pole. In the high exhaustion, however, after the 
ray of light had dipped to the magnet it did not recover 
itself, but continued its path in the altered direction. 
During these experiments another property of this mole- 
cular discharge has made itself very evident, although I 
have not yet drawn attention to it The glass gets very 
warm where the green phosphorescence is strongest. The 
molecular focus on the tube, which we have just seen 
(Fig. 12) would be intensely hot, and I have prepared an 
apparatus by which this heat at the focus can be intensified 
and rendered visible to all present. This small tube (a) 
(Fig. 16) is furnished with a negative pole in the form of a 
cup (6). The rays will therefore be projected to a focus 
