434 Molecular Physics in High Vacua. [June, 
and you see I can deflect the focus of heat just as I 
did the luminous focus in the other tube. By shifting 
the magnet I can drive the focus up and down, or draw it 
completely away from the metal, and render it non-luminous. 
Fig. 18. 
I withdraw the magnet, and let the molecules have full 
play again ; the metal is now white-hot. I increase the 
intensity of the spark. The metal glows with almost insup- 
portable brilliancy, and at last melts. 
There is still another property of this molecular dis- 
charge, and it is this : — You have seen that the mole- 
cules are driven violently from the negative pole. If I place 
something in front of these molecules, they show the force 
of impact by the heat which is produced. Can I make this 
mechanical action evident in a more direct way ? Nothing 
is simpler. I have only to put some easily moving object in 
the line of discharge in order to get a powerful mechanical 
action. Mr. Gimingham, with great skill, has construdted 
a piece of apparatus which I will presently put in the 
electric lantern, so that all will be able to see its adtion. 
But first I will explain the construction by means of this 
diagram (Fig. 19). The negative pole ( a , b) is in the form of a 
