J. Trowbridge — Doppler Effect in Positive Rays. 245 



Aet. XVIII.— The Doppler Effect in Positive Bays ; by 

 John Trowbridge. 



The discovery of canal rays by Goldstein, and that of the 

 Doppler effect in these rays, marks an epoch in the study of 

 the discharge of electricity through gases; for before these 

 discoveries the multitude of confusing effects which arise in 

 the space between the anode and the _, 1 



cathode made it difficult to observe 

 any translation movement. The 

 space, however, behind the cathode 

 is comparatively free for the passage 

 of the positive ions. 



We now recognize, in addition to 

 the positive rays behind the cathode — 

 the canal ray — retrograde positive rays 

 which are directed to the anode, or 

 rather away from the cathode in the 

 direction of the anode.* This later 

 discovery leads one to expect that the 

 Doppler effect should be found also 

 between the anode and the cathode. The result of my study 

 shows that the effect does exist in this region and indicates 

 a movement away from the cathode and toward the anode. 



The form of tube I have employed is represented in fig. 1. 

 The slit of the Rowland grating was at X for the retrograde 

 rays and at Y for the canal rays; A being the anode and C 

 the cathode. The Rowland grating gave, in the order of spec- 

 trum I employed, six Angstrom units to nine-tenths of a milli- 

 meter. The effect was observed with respect to the hydrogen 

 line 4861*5 and the change in refrangibility was measured by 

 comparison with the solar spectrum, which was photographed 

 immediately beneath the gaseous line without changing the jaws 

 of the slit. The amount of the change in refrangibility was 

 sensibly the same as in the canal rays. 



The difference of potential between the anode and the cathode 

 varied between five thousand and ten thousand volts ; and the 

 current from ten to five milliamperes furnished by a storage 

 battery of ten thousand cells. A current of running water 

 provided a large and steady resistance. 



The appearance of the discharge at the cathode has often 

 been described. The cathode appears to be the base of two 



* Wehnelt, Wied. Ann., 1899, p. 421 ; Eunge and Baschen, Wjed. Ann., 

 lxi, 1897, p. 644; Paschen, Wied. Ann., xxiii, p. 247; Villard, Comptes 

 Kendus, cxliii, p. 673, 1906; Goldstein, Phil. Mag.. March, 1906; Jacob 

 Kunz, Phil. Mag., July, 1908, p. 161 ; J. J. Thomson, Oct., 1908, p. 657. 



Am. Jour. Sci. — Fourth Series, Vol. XXVII, No. 159. 

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