the Earth' s Penetrating Radiation on Land and Sea. 525 



the open sea. Moreover, as the value found for " q " over 

 the water of Toronto Bay with a receiver of the same material 

 as the one used in this investigation was 4*4 * ions per c.c. per 

 sec., and as Simpson and Wright obtained 41 per c.c. per sec. 

 for " q " on a small skiff on the open sea, it would appear that 

 the effective radiation from a large ship such as the ' Grampian ' 

 is practically the same as that from a vessel of the size of the 

 ' Terra Nova ' f. 



A point of! interest in connexion with the readings taken 

 on the steamer (which, however, may possibly be purely 

 accidental) is the gradual drop which they show after leaving 

 Glasgow until Sept. 21st was reached. The reading opposite 

 this date is the mean of those taken during the day preceding 

 the passage through the Straits of Belle Isle. It is higher, 

 it will be seen, than any of those taken during the voyage. 

 The reading 5*78 ions per c.c. per sec. was taken when in the 

 Biver St. Lawrence near Rimouski, and the last, 5'92 ions 

 per c.c. per sec, as the steamer was approaching Quebec. 

 The numbers it will be seen show a gradual rise during the 

 passage up the river. 



III. On Variations in the Intensity of the Penetrating 

 Radiation. 



Although the time at the disposal of the writer in making* 

 the observations was limited, and as a consequence they were 

 not as extensive as one would wish to have them, still they 

 were sufficiently numerous at two stations in Great Britain 

 to show that if variations did occur at these two places, such 

 variations in the intensity were not greater than at most two 

 or three per cent., which is about the accuracy with which 

 readings can be made with the instrument used. 



The successive readings taken at Cambridge on a number 



* Loc. cit. 



t [Note added June 30, 1912.] In some measurements made by the 

 writer in collaboration with Mr. A. R. McLeod since the presentation of 

 this paper in May, with the receiver used in the experiments described 

 above, a value was obtained for ll q" of 4*46 ions per c.c. per sec. over 

 the waters of Lake Ontario. In this case the observation station was a 

 small platform supported by four lor g gas-pipes driven into the sand at 

 a point in the Lake where the water was foiir metres deep. It is 

 interesting to note that the value is practically the same as that obtained 

 bv Wright and the writer in 1009 on the ice over the waters of Toronto 

 Bay 



