NO. 1863 BIBI^IOGRAPHY OF CANAL RAYS — FULCHER 309 



Eflfect not due to presence of H2 as impurity. Brightness of fluorescence 

 patch measured photometrically and found to be the 

 same whether extreme precautions were taken to elimi- 

 nate H2 or not: Tm6(295) ; Tm7(36o) ; of. Wio(2i2). 

 Hydrogen canal rays abundant when no hydrogen ions can be detected 

 in other parts of the tube: Tm8(68o). 



As pressure increases, patches enlarge, overlap and merge to form the 

 continuous, fairly straight streak: Tm3(574). 



9. secondary emission of negative rays from a metallic 

 surface struck by canal rays. 



Intensity of Secondary Radiation. 



Function of the velocity of the canal rays, few negative rays for low 

 tensions (600 v.) : Fi(i56) ; F3(30i). 

 Kinetic energy of canal rays must exceed a certain value: Pry 1(448). 

 Function of the angle of incidence. 



Much less for normal than for greater angles of incidence in case of 



Al and brass: Fi(i53) ; F2(749) ; Au2(3is) ; F3(3o6). 

 In case of Cu, variation is slight: Fi(i53); F3(3o6). 

 Depends on the metal struck. 



For high tensions (30,000 to 7S,ooo v.), the secondary negative cur- 

 rent emitted is the following per cent of the canal ray 

 current : Al, 300 per cent ; Zn, 170 per cent ; Cu and Ag, 

 TOO per cent; Pt, 80 per cent: Fi(i55). For brass, 

 6,000 v., 45 per cent: Au2(3r4). 

 Measurements complicated by the positive reflection, which for the 

 lower tensions may overbalance the negative emission : 



Fidss). 



Relation to cathode fall. 



Metals which used as cathodes have the greatest cathode fall for a 



given pressure, show the least negative emission when 



struck by canal rays: Ew3(3io). 

 Velocity. 



Not very great, since emission is stopped if electrode is charged to a low 



positive potential: Tm2(2i3). 

 Varies considerably among the rays: Au2(3i8). 

 Average Velocity, that is, the velocity of most of the rays, measured by 



deflecting them magnetically through a curved canal, 



and determining the current received by an electrode at 



the end as a function of the field strength : F2(749). 

 Value is 3.2 to 3.5 x 10* cm. for Pt or Al : F2(749) ; F3(30i, 304). 

 Independent of the velocity of canal rays: F2(749). 

 Independent of the gas (H2 or air) : F2(749). 

 Independent of the angle of incidence: F2(749). 

 Independent of the metal struck (Pt or Al) : F2(749) ; F3(30i, 304). 

 Same as that of secondary rays produced by cathode rays striking a 



metal: Ew3(3io). 

 Distribution of the rays among different velocities shown by curves : 



F3(303). Varies with gas and with metal: F3(304). 



