822 S. Kinoshita, $. Nishikawa, and S. Ono on Amount 



Our principal object in the present experiments was to find 

 the relative amounts of these two emanations at Tokyo. We 

 have then attempted to elucidate the procedure of deposition 

 of the active matters on a negatively charged wire. 



When this paper was ready to appear, Traite de Radio- 

 activite, by Madame Curie, came in our hand, in which 

 similar problems are dealt with *. We have, however, treated 

 the problem from a different point of view, of which the full 

 account will be here given. 



Experiments. 



(2) Two copper wires, each '5 mm. thick, 27 metres long, 

 and insulated at both ends, were horizontally stretched in 

 the N.S.-direction between two posts at the heights of 0*5 and 

 1'5 metres respectively from the ground in the south yard 

 of our laboratory building. These wires were connected to 

 the negative terminal of a Wimshurst machine driven by a 

 motor and maintained at a potential of about — 11,000 volt^, 

 which was measured with a Kelvin electrostatic voltmeter. 



When the wires had been exposed to the atmosphere for a 

 definite time (usually 4 hours, in some cases 24 hours), they 

 were removed, and the middle portion, 20 metres long, of 

 each was quickly coiled round a brass cage d'2 cm. square, 

 which was then introduced into a square electroscope with 

 sides 11*3 cm. The activity of the deposits on each wire 

 was then measured in the usual way for about a day. We 

 expressed it in terms of the scale divisions on an ocular 

 micrometer divided in y 1 ^ mm. passed by the gold-leaf per 

 second. As a matter of fact, the rates of discharge of the 

 two electroscopes were not exactly the same. We have, 

 therefore, reduced them to a common standard by the aid of 

 the Y-rays from a radium preparation placed at equal dis- 

 tances from the electroscopes, when the wires were not 

 active. The four rods constituting the side-frames of the 

 cages were provided each with 55 grooves in regular 

 intervals of -^ cm., which served to keep a wire in the same 

 definite position. 



The decay-curve of the activity thus obtained can be 

 satisfactorily explained by the assumption, as has hitherto 

 been made, that radium A and thorium A were deposited on 

 the wire during exposure. 



Although we were not able to measure accurately the 

 activity of the radium A, on account of its rapid decay — a 

 few minutes being unavoidably lost in winding the wires in 

 electroscopes — the activity due to radium C and also to the 

 thorium deposits, and consequently their corresponding values 

 * Traite de Radioactivite, vol. ii. p. 484 (1910). 



