108 



Mr. W. Crookes on 



[Dec. 5, 



Mechanical Action of Projected Molecules. 

 When the coil was first turned on, the thin film was driven back at 

 the moment of becoming phosphorescent, showing that an actual 

 material blow had been given by the molecules. Experiments are 

 next described in which this mechanical action is rendered more 

 evident. A small rotating fly, capable cf being moved about in any 

 part of an exhausted bulb, is used as an ndicator, and by appropriate 

 means the molecular shadow of an aluminium plate is projected along 

 the bulb. Whether entirely in, or entirely out of the shadow, the 

 indicator scarcely moves, but when immersed so that one-half is ex- 

 posed to molecular impact the fly rotates with extreme velocity. 



Magnetic Deflection of Lines of Molecular Force. 



With this apparatus another phenomenon was investigated. It is 

 found that the stream of molecules, whose impact on the glass is 

 accompanied by evolution of light, is very sensitive to magnetic in- 

 fluence, and by bringing one pole of an electro-magnet — or even of 

 a small permanent magnet — near, the shadow can be twisted to the 

 right or to the left. 



When the little indicator was placed entirely within the molecular 

 shadow, no movement was produced. As soon, however, as an adjacent 

 electro-magnet was excited, the shadow was deflected half off the indi- 

 cator, which immediately rotated with great speed. 



The Trajectory of Molecules. 



The amount of deflection of the stream of molecules forming a 

 shadow is in proportion to the magnetic power employed. 



The trajectory of the molecules forming the shadow is curved when 

 under magnetic influence ; the action of the magnet is to twist the 

 trajectory of the molecules round in a direction at an angle to their 

 free path, ancl to a greater extent, as they are nearer the magnet : 

 the direction of twist being that of the electric current passing round 

 the electro-magnet. 



Laws of Magnetic Deflection. 



An apparatus was constructed so that the deflection of a spot of light 

 was observed instead of that of a shadow ; a horseshoe magnet being 

 placed underneath the negative pole to deflect the trajectory. The 

 action of the north pole being to give the ray of molecules a spiral 

 twist one way, and that of the south pole being to twist 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. 



The ray of molecules does not appear to obey Ampere's law, as it would 

 were it a perfectly flexible conductor, joining the negative and the posi- 



