[WRIGHT] VARIATIONS IN THE CONDUCTIVITY OF AIR io8 



From the values of " q," given in Table XI;, for the three receivers, 

 we obtain for the difference between the ionization in the laboratory 

 and over the water the numbers 6.7, 7.4 and 6.0 for tlie receivers of 

 lead, zinc and aluminium respectively. These values then may be taken 

 as given by a measure of the relative ionization in the three receivers 

 due to that portion of the radiation from the earth which was cut off 

 by the water, together with the secondary rays induced by the radiation 

 in the different cylinders. That the actual numbers obtained for " q " 

 at any observing station were not in the same ratio as these decreases 

 is a conclusive proof that the ionization measured at these stations was 

 not due entirely to the radiation from the earth. 



It might be well to call attention again to the fact that these de- 

 creases in the receivers of lead, zinc and aiimainium of 6.7, 7.4 and 

 6.0, which are in the ratio of 1.1 to 1.23 to 1.00, must give a true 

 measure of the total ionization in the three receivers which is due to 

 a portion, at least, if not the whole of the penetrating radiation from 

 the earth. If then we could obtain cylinders of lead, zinc and- alu- 

 minium free from active impurities and possessing no intrinsic activity, 

 we should expect the values for " q "' at every point on the surface of 

 the earth to be in this ratio. 



Emphasis might also be laid upon the extremely low values found 

 for the ionization over the water when the cylinders were freshly cleaned 

 and freshly filled with filtered air. These values of 8.6, 6 and 6.5 

 obtained for the receivers of lead, zinc and aluminium are very much 

 lower than those obtained by any other observer under any conditions, 

 and afford a conclusive proof of the efficacy of Lake Ontario water as 

 a screen for the earth's penetrating radiation. 



The experiments made at Stations 5 and 6 are of special interest, 

 as the conductivity obtained at these points was practically the same as 

 that obtained in the experiments on the surface of the lake, which shows 

 that the sand was entirely free from the radioactive substances which 

 were probably present in the clays and rocks at other points of observ- 

 ation. 



VI. — Secondaey Kays Induced by the y Eays from Eadium. 



To determine if this ratio of 1.1 to 1.23 to 1.0 for the three receivers 

 of Ph., Zn. and Al. would be found to hold also in the case of ionization 

 due to the w rays from radium, a series of measurements was under- 

 taken with the electrometer used before. 



A quantity of radium bromide encased in a lead box with walls 

 2 cms. thick, was used as the source of the penetrating rays, and the 

 ionization measured in each receiver for different distances between it 



