70 '^he Philippine Journal of Science i^i* 



A thorough study of the subject involves the careful mapping of 

 the wind trajectories for the given location for the different 

 seasons of the year and for the different parts of the day. By 

 this means it should be possible to determine, at least ap- 

 proximately, whether the air tested had previously passed for 

 any considerable time over the land or over the ocean. 



Several observers have made determinations of the diurnal 

 variation by the active-deposit method. Simpson ^^ made three 

 determinations a day — morning, noon, and evening — during the 

 greater part of a year, and found a maximum in the morning and 

 a minimum about midday. Gockel,^® at Freiburg, likewise 

 obtained a maximum in the early morning and sometimes a low 

 value about noon. Dike," at Cambridge, found a minimum at 

 about 6 p. m. followed by a rapid increase to a maximum at 1 

 a. m., which was followed by a slight drop with another maximum 

 at 4 a. m. Dike's observations, however, are not sufficiently 

 extensive to justify any general conclusions. As has been 

 pointed out, the active-deposit method is not adapted to an 

 accurate determination of the emanation content, and the diurnal 

 variation observed may be largely due to changes in the 

 nucleation or other conditions of the atmosphere. 



The solution of the problem of the diurnal and annual varia- 

 tion will be attained only by a series of careful observations 

 extending over a long period of time. We plan to continue the 

 observations during the coming year in the hope of being able 

 to learn more concerning this interesting and important phase 

 of the work. 



PAET II. VARIATION OF THE RADIUM-EMANATION CONTENT OF THE 

 ATMOSPHERE WITH ALTITUDE 



It has been shown by observations taken in different parts of 

 the world that radium emanation is everywhere present in the 

 atmosphere. The source of the emanation is undoubtedly the 

 radium contained in the earth's crust. Since the half-value 

 period of radium emanation is 3.86 days, it is to be expected 

 that it will be transported by air currents to a considerable 

 distance from its source before a large amount of its activity 

 has been lost. Observations taken by Eve,'* Simpson and 

 Wright,'* and others show that even over the centers of the 



'* Loc. cit. 



"Phys. Zeitschr. (1904), 5, 591. 



"Terr. Mag. (1906), 7, 125. 



"Phil. Mag. (1907), 13, 248; Terr. Mag. (1909), 14, 25. 



"Proc. Roy. Soc. (1911), A, 85, 175. 



