832 S. Kinoshita, S. Nishikawa, and S. Ono on Amount 



q is duo partly to the penetrating rays coming from the 

 active matters contained in the soil, and partly to the presence 

 of the radium and thorium emanations and their successive 

 products of disintegration in the atmosphere. 



If 7e 7 Ya, and 7c are the total numbers of ions produced 

 in the whole range by each a-partiele emitted from the 

 radium emanation, radium A, and radium C respectively, and 

 7 their sum, and if je, 7b', and <yc are those for the thorium 

 emanation, thorium B, and thorium C respectively, and 7' 

 their sum *, then q is approximately given by 



?=X E N E (7) +\ E 'N E ' (7') + % 



where \ E ' is the constant of transformation of the thorium 

 emanation, N E ' the number of atoms of the thorium emana- 

 tion per cubic centimetre of air, and q the number of the 

 negative ions produced per second by the penetrating rays. 

 Therefore 



7i E N E 



N A .+ = 



is the number of the charged particles of radium A in air in 



equilibrium, and this must be substituted for — — ? in the 

 expression for Q. A 



From his experiment on a similar subject, Evet concluded 

 that the collecting distance of a wire raised to — 10,000 volts 

 was about 40 to 80 cm. It appears to us more reasonable 

 to introduce the notion of the contributing volume than that 

 of the collecting distance used by him. 



Amount of the Emanations present in the Atmosphere. 



(13) We have so far expressed the electric force in terms 

 of the charge per unit length of the wire. If —fii and — /i 2 

 are the charges per unit length of the wires at heights hi 

 and h 2 respectively above the ground, then the potential V 

 at any point is given by the equation 



Y=2^ 1 log^ 7 4-2^iog^,, 

 r 1 r 2 



where r x and r 2 are the distances of the point from the wires 

 respectively, and r/ and r 2 ' those from the corresponding- 

 images of the wires with respect to the surface of the earth. 



* Since 4 a-particles are apparently emitted from the thorium emana- 

 tion for one from thorium B or O, y 1 = 4yE'+7B' + yc'- 

 t Eve, Phil. Mag. July 1905. 



