X, A. 1 



Blackwood: Radioactivity of Atmosphere 



47 



Table II. — Diurnal variation of the active deposit collected on 

 Mount Maquiling, Laguna Province, Luzon. 



Date. 



1914. 



May 16 



Do 



Do 



Do 



Do 



Do..- - 



May 17 



Do 



Do 



Do 



Do 



Do 



May 18 



Do 



Do 



Do - 



Do 



Do 



Do 



May 19 



Mean day value... 

 Mean night value. 



Time af- 

 ter mid- 

 night. 



Hrs. 



8i 

 10 

 12 

 14 

 17i 

 22 

 3 

 7 

 9i 

 13i 

 16J 

 19 

 4 

 6J 

 9 

 12 

 14i 

 18 

 21 



n 



Recipro- 

 cal of 



time for 

 leaf to 



move 40 



divisioHB, 



0.017 

 0.017 

 0.014 

 0.008 

 0.010 

 0.008 

 0.008 

 0.012 

 0.029 

 0.017 

 0.040 

 0.021 

 0.005 

 0.005 

 0.008 

 0.012 

 0.022 

 0.014 

 0.004 

 0.008 



0.007 

 0.09 



SUMMARY 



1. The mean day-value of the active deposit at Manila is about 

 the same as that of Wolfenbiittel. 



2. (a) There is a large and fairly regular diurnal variation 

 of the active deposit at Manila, the mean night-value being 

 about three times that of the day. (b) The mean active deposit 

 seems to vary with the humidity, but in the individual curves 

 there are wide divergences, (c) There is no evident relation 

 between the wind and the amount of deposit collected. 



3. (a) The active deposit collected on Mount Maquiling, eleva- 

 tion 1,140 meters, is about twice that of Manila, (b) The diur- 

 nal variation on the mountain is apparently the inverse of that of 

 Manila, the night collection being smaller than the day. 



4. The half-period value found at Manila is about sixty-two 

 minutes, which corresponds to less than 15 per cent thorium 

 active deposit. 



