8 Duane — Emission of Electricity. 



ured by the piezo-electric quartz, and column 1 the time in 

 minutes after the electrode had been withdrawn from the ema- 

 nation. In order to compare them, I have drawn this curve 

 and the curve representing . the decay of the positive current 

 for the brass surfaces (Table II, column 2) together in figure 2. 

 Curve 1 represents the decay of the a ionization current in air 

 at atmospheric pressure, and curve 2 that of the positive cur- 

 rent in vacuum. The scales of the two curves were so chosen 

 as to make them coincide at t — 70. It is easily seen that they 

 do not coincide at other points, the curve representing the 

 charge carried by the rays being much steeper than the other. 



14. The explanation of this undoubtedly is that radium B, 

 which under ordinary circumstances produces an almost inap- 

 preciable amount of ionization, does emit a very appreciable 

 number of negatively charged rays. For the sake of compari- 

 son, I have calculated the theoretical curve that one should get 

 under the supposition that radium B emits as much electricity 

 during its change as radium C does during its. This is curve 

 3 in the figure. It is drawn under the assumption that there 

 is on the electrode, to start w T ith, equilibrium amounts of 

 radium A, B and C, i. e., amounts that are inversely propor- 

 tional to their respective decay constants, and that initially the 

 quantity of radium B present emits as much electricity per 

 second as does the quantity of C present. The scale of the 

 theoretical curve was chosen so as to coincide with the others 

 at t — 70, and it appears that the experimental curve 2 is a 

 little steeper even than the theoretical one. In making the 

 calculations I used constants corresponding to decay to half 

 value in 3, 28 and 21 minutes respectively, for radium A, B and 

 C. It is probable that the last two values, 28 and 21, are too 

 high. Slightly smaller values would bring the theoretical 

 curve closer to the experimental one. 



All the curves that I have examined representing the posi- 

 tive currents and the \ algebraic sum of currents, are steeper 

 than the theoretical curve. Curves representing negative cur- 

 rents are usually somewhat less steep than those representing 

 positive currents, but lie much nearer curve 3 than curve 1. 

 It follows that radium B must emit its full share of negative 

 electricity when changing into C. 



The theoretical curve representing radium C alone coincides 

 so closely with curve 1 that I have not drawn it in the figure. 



15. In some interesting experiments H. W. Smith* has 

 shown that radium B produces a slight ionizing effect. He 

 attributed the ionization to easily absorbed rays, probably /3- 

 rays. The ionization produced by rays from radium B can be 

 shown very easily with the aid of the apparatus used in the 



* H. W. Schmidt, Physikal. Zeitschrift, vi, 897-903, 1905. 



