524 Prof. J. C. McLennan on the Relative hit en skies of 



by reason of the introduction of radium or other radioactive 

 substance. 



Table I. 







" q." 







The number of ions 



Observation Point. 





produced in the re- 

 ceiver per c.c. per 

 second, 



1. Cambridge, England 



9-03 



2. PJowland, Midlothian, Scotland 



8-32 

 9-08 





4. The Meteorological Observatory, Toronto 



5. The Lawn of the Meteorological Obser 





8-88 



vatory. 



6-74 



Toronto. 







6. The Atlantic Ocean, on s-.s. ' Grampian,' 



sailing 





ex Glasgow, Sept. 16, 1911. 







Sept. 17 6-12 







IS ...... 6-51 







19 ::i... 5-97 







20 5-42 







21 6 58 







22 5-66 







23 ...... 5-78 







24 5-92 







Mean 6" 03 





603 



From the numbers given in the table it is evident, in the 

 first place, that the value obtained for u q" was {practically 

 the same when the point of observation was taken inside 

 either a brick or a stone structure at points so far separated 

 from each other as Cambridge, England, Bowland, Scotland, 

 and Toronto, Canada. 



In the second place, from the measurements made at the 

 Meteorological Observatory, Toronto, it is clear that tbe 

 building itself contributes in a measure to the penetrating 

 radiation, for the readings obtained on the lawn near that 

 building were on the average more than 1 ion per c.c. per 

 Second less than those taken inside the observatory. 



In the third place, the numbers show that all the values 

 obtained for " q " on the s.s. ' Grampian ' were less than an.y 

 of those obtained on land. 



Further, the mean of these readings, 6'03 ions per c.c. per 

 sec, agrees well with the reading obtained by Simpson and 

 Wright *, 6*3 ions per c.c. per sec, on the ' Terra Nova ' on 



* Simpson & Wright, Proc. Koy. Soc. Ser. A, vol. lxxxv, p. 175 (1911). 



