July 10, 1879] 



NATURE 



253 



v; leiitly from the ne;ative ro'e- If I i''-^c'= S5me:li'nr i 1 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 ea-ily moving object in the line of discharge in order to get 

 a powerful mechanical action. Mr. Gimingham, with great 



Fig. 16. 



skill, has constructed a piece of apparatus which I will presently 

 put in the electric lantern, so that all will be able to see its 

 action. 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 very" shallow cup. la front of the cup is a mica screen 



\ 



vu 



Fig. 17. 



(<r, <j), wide enough to intercept nearly all the molecular rays 

 coming from the negative pole. Behind this screen is a mica 

 wheel (e, f) with a series of vanes, making a sort of paddle-wheel 

 of it. So arranged, the molecular stream from the pole a b will 

 nearly all be cut off from the wheel, and w hat escapes over and 



under the screen will hit the vanes equally, and will not produce 

 any movement. I now put a magnet, g, over the tube, so as to 



deflect the stream over or under the obstacle cd, and the result 

 wiirbe rapid u.otion in one or the other direction, according to 



