6 Duane — Emission of Electricity. 



11. The decay of the rate of discharge of electricity from 

 the electrode with B put to earth was studied. For this pur- 

 pose a zero method of measuring the currents is necessary, and 

 the piezo-electric quartz was chosen, for in measuring currents 

 by it the electrode is always held at zero potential. The cur- 

 rents measured by the quartz with B put to earth, but other- 

 wise under the same conditions as before, appear in column 5 

 of Table II. These data represent a series of measurements 

 distinct from that tabulated in columns 2 and 3. In order to 

 reduce the readings to the same scale the positive currents 

 under an electromotive force of 2*2 volts were measured several 

 times, for instance at £=22, 36 and 64. With these values for 

 comparison the measurements with the quartz were reduced 

 to the same scale as the others. It will be noticed that the 

 discharge current e for zero potential is with two exceptions 

 some 10 per cent less than the -§- algebraic sum of the currents 

 tabulated in column 4. This difference is in part at least due 

 to the Volta electromotive force, which, as I mentioned above, 

 always acted in such a direction as to reduce the discharge of 

 negative electricity from the electrode. From these experi- 

 ments it appears that equations (1) and (2) are roughly correct. 



12. We can, however, analyze the currents in other ways. 

 We can, for instance, say that the currents are due to two 

 streams of electricity s x and s 2 projected from the surfaces of 

 the electrode and tube respectively ; that when no electromotive 

 force acts the current is 



e = Sl - s 2 



and that when an electromotive force is applied one of the 

 two streams, s 1 or s 2 is more or less checked. If A^ and As 2 . 

 are the changes produced by the electromotive force, the 

 positive and negative currents are 



K — s i — ( 5 2 — A5 J = s i — * 2 + As <> 



i 2 = s t — As x — s 2 = s 1 — s 2 — ASj 



If A.s l >s 1 — s 2 , there would be a resultant current away from 

 the electrode in the second case. Applying this theory to the 

 data for the brass electrode, it appears that for 2*2 volts As, 

 and As 2 must be some 50 per cent larger than s,—s 2 ; that is, 

 there must be a large number of slow-moving /3-particles pro- 

 jected from both surfaces, rays that 2 volts will stop. Such 

 rays are produced by polonium,* radiumf and other radio-active 

 substances. The experiments further show that approximately 

 A.Sj=As 3 for the same electromotive force. The assumption 

 made in this theory is that the value of s 1 does not depend on 



* J. J. Thomson, Nature, Dec. 15, 1904. Proc. Camb. Phil. Soc, xiii, Pt. 1 T 

 p. 39, 1905. 



+ E. Eutherford, Radio-activity, pp. 151-154. 



