174 Mr. W. Makower on the Number and Absorption 



In order to eliminate errors due to faulty insulation and to 

 the ionization of the residual gas between the tube containing 

 the emanation and the brass cylinder, observations were made 

 first with the tube containing the emanation connected to the 

 positive pole, and then to the negative pole of twenty storage- 

 cells. By taking the mean of the charges acquired by the 

 brass cylinder in a fixed time in these two cases, the above 

 mentioned errors were eliminated. 



Assuming that all the /3 rays are stopped by the brass 

 cylinder, it is clear that, if the capacity of the glass tube 

 together with that of the electrometer and connexions is 

 known, the total negative charge emitted per second by the 

 known quantity of radium C contained in the glass tube 

 can be calculated. Now it is known that the charge carried 

 by the /3 particle is 4'65x 10~ 10 electrostatic unit. Hence, 

 from the above measurements, the number of /3 particles 

 emitted by the quantity of radium C in equilibrium with 

 one gram of radium can be calculated. In the experiments 

 here to be described, the current passing from the emanation 

 to the brass cylinder was so large that it was necessary to 

 insert, in parallel with the electrometer, a large capacity. 

 On this account it was necessary to determine the capacity 

 of the electrometer and its connexions only roughly. This 

 was done by screening off part of the radiation from the 

 tube containing the emanation by glass tubes placed over it, 

 and, when the radiation had been sufficiently reduced 

 to get readable deflexions of the electrometer, comparing 

 the deflexion produced in a given time with and without 

 a condenser of suitable capacity in parallel with the 

 electrometer. 



It has already been mentioned that these measurements 

 were undertaken with a view to avoiding errors due to 

 secondary radiation of the (3 type set up when /3 rays 

 impinge on an obstacle. The following considerations will 

 show that the method described above is calculated to reduce 

 such errors to a minimum. The radiation proceeding from 

 the tube containing the emanation fell upon the brass 

 cylinder, where it was absorbed. During this process 

 secondary rays were emitted from the inside of the brass 

 cylinder, and so would have escaped detection by the electro- 

 meter had not steps been taken to reabsorb them by the brass 

 cylinder. Now any radiation proceeding from the inside of 

 the walls of the brass cylinder will impinge on some other 

 portion of the cylinder, since this forms an almost perfect 

 enclosure, and will therefore ultimately all be absorbed and 

 give up its charge, except for the small amount of radiation 



