IX. A, 1 Wright and Smith: Radium Emanation 65 



is approximately the same as that found by Satterly for Cam- 

 bridge by the same method and by Ashman at Chicago by the 

 condensation method, but is considerably greater than that 

 found by Eve for Montreal. If we take into account the fact 

 that only a fractional part of the emanation is removed from 

 the solution by bubbling air through the cold solution, then 

 we must multiply the above result by the reduction factor, equal, 

 according to our tests made under identical conditions, to 79.2 

 per cent. This would give us 82.5 X lO-^^ (i04.28 X lO-^^ 

 X 0.792) gram as the average amount of radium which would 

 be necessary to maintain in radioactive equilibrium the radium 

 emanation in 1 cubic meter of the atmosphere for Manila. 



In our determinations the variation in the radium-emanation 

 content of the atmosphere is somewhat less than that obtained 

 by other observers, the ratio of the maximum to the minimum 

 being approximately 4 to 1, while Eve gets a ratio of 7 to 1, 

 Satterly 10 to 1, and Ashman 5 to 1. Since in most respects the 

 annual variation of climatic conditions is much less for Manila 

 than at any of the other places where similar observations haV6 

 been taken, it is probably to be expected that the variation in 

 the amount of radium emanation in the atmosphere would be 

 less. The one meteorological factor subject to the greatest 

 variation in Manila is the rainfall, which during several months 

 of the year is extremely heavy, while for part of the year the 

 precipitation may be almost negligible. The mean of the obser- 

 vations taken during the rainy season in July, August, and Sep- 

 tember is 103.2 X 10-12 gram as compared with 104.5 X 10-^^ 

 gram for observations in the months of December, January, and 

 February, when the precipitation is very light. It is evident 

 from these values that no reliable conclusion can be drawn from 

 the average value of observations extending over a definite season 

 of the year as to the variation with meteorological conditions. 

 A comparison of the observed values of the radium-emanation 

 content with the corresponding meteorological data from the 

 Manila Observatory shows, however, an Interesting and a fairly 

 definite correlation. The Manila Observatory is located at a 

 distance of about 400 meters from the Bureau of Science, so 

 that the two sets of data practically coincide as to location. In 

 Table VII are given the meteorological data which seem to have 

 the most direct bearing on the variation of the emanation content. 

 The only determinations which are omitted from the table are 

 those for day exposures which, for reasons explained later, we 

 have included in a separate table. 



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