Doppler Efect in Positive Rays. 523 



of the cathode on the glass. These striae can be localized at 

 a definite point by bringing the edge of the disk of the 

 cathode nearer the wall of the tube ; and we then have a 

 source of positive rays which is analogous to that formed by 

 pushing a glass tube surrounding the anode into the Crookes' 

 space *. 



The heating and oxidizing effect from the positive particles 

 of these striae is very marked, especially when the canal 

 region is small, and is much greater than any effect produced 

 by the canal rays in a possible rebounding from the end 

 of the canal region. The photographs of cathode discs 

 exhibit this effect of the positive rays coming from the 

 striae. 



Fig. 3 a (PL XIV.) is a photograph of the back of a cathode 

 made of aluminium from as pure clay as could be obtained. 

 The disk was "75 mm. thick, and the hard surface formed by 

 the iron rolls was left upon it. The heat from the positive 

 rays coming from the striae caused the occluded gases of the 

 aluminium to form blisters on its surface. 



Fig. 3 b is a photograph of the back of a cathode formed 

 from the same quality of aluminium as in fig. 3 a, except that 

 the plate of aluminium was treated with nitric acid to remove 

 any trace of iron coming from the rolls. The surface thus 

 lost its polish and hardness. A very black deposit formed 

 under the effect of the positive rays of the striae, which was 

 probably carbon from the aluminium. 



Fig. 3 c was a cathode formed from ordinary commercial 

 aluminium 1*5 mm. thick. It represents the blackening 

 which results from long running of the discharge. At 

 increased exhaustions and during this lont>- use of the tube 

 the striae shift their position, and the back of the cathode 

 shows a general discoloration. 



Fig. 3d represents the front of the cathode of fig. 3c. The 

 centre is bright, while the edges are discoloured. Goldstein 

 has noticed that positive rays remove deposits. 



Fig. 4 is a photograph of the canal rays which shows 

 also the luminosity on the back of the cathode produced 

 mainly by the striae. 



The order of spectrum produced by the Rowland grating 

 gave an interval of "9 millimetre to six Angstrom units. 

 The approximate interval between the Doppler effect on 

 both sides of the stationary hydrogen line 486 I'D was three 

 Angstrom units ; the difference of potential between the 



* E. Wiedemann, Wied. Ann. lxiii. 1897, p. 242. 



