96 ROYAL SOCIETY OF CANADA 



In the results which will be given later it will be seen that varia- 

 tions amounting to as much as 75 per cent were obtained in the con- 

 ductivity by a change in the observing station, and from the results 

 obtained and given in Tables IX, X and XI it will bo seen that any 

 variation in conductivity due to daily changes in the value of the pene- 

 trating radiation from the eartli which might have existed, were negli- 

 gible in comparison with the variation in the conductivity due to a 

 change in the point of observation. 



(c) — Secondary radiation from the walls of a room. 



In view of the existence of a penetrating radiation at the surface 

 of the earth havmg its origin either in the atmosphere or in the soil. 

 and in view of the production by such radiations of secondary rays at 

 the surface of substances traversed by them, it was thought advisable, 

 before going on with the main part of the investigation, to see how 

 far the influence of a secondary radiation excited in the walls of a 

 room could be detected from those walls. 



To obtain some information on this point, two plans suggested 

 themselves, — (l)to place the conductivity chamber at a selected dis- 

 tance from a wall and to study the secondary rays excited at that wall 

 by a quantity of radium placed at points on a circle with the chamber 

 at its centre; (2) to study the variation in the ionization in a metal 

 receiver with the radium at a fixed distance from the wall and the cham- 

 ber placed at points on a circle with the radium as centre. A set of 

 measurements was made by following the first plan, but time has not 

 permitted the carrying out of a series of observations with the second 

 arrangement. 



The electroscope, provided with a zinc receiver, in these measure- 

 ments was placed at a distance of about one metre from the wall of a 

 large room, and the radium enclosed in a lead box with walls 2 cms. 

 in thickness, was moved around the circumference of a circle having 

 as centre the cylinder and as radius the distance of the same from 

 the wall. 



The values for " n," the number of ions per c.c. per sec. due to 

 the primary radiations from the radium, as well as the radiation emitted 

 by the brick wall, together with the corresponding secondary rays excited 

 in the metallic cylinder, are given in Table Yll, and shew a regular 

 decrease in the ionization as the distance of the radium from the wall 

 was increased, with indications of a possible smaller maximum for a 

 definite angle subtended at the wall by the line joining the radium with 

 the electroscope. A curve representing the variation of " n " with 

 the distance of the radium from the wall is given in Fig. 6. From 



