72 The Philippine Journal of Science i9i4 



collected from a standard solution of radium bromide, changes 

 of pressure and nucleation in the atmosphere will have no effect 

 on the final results. The same is true for the ionization produce^ 

 by the emanation introduced into the testing vessel. Conse- 

 quently, the method should give an accurate determination of 

 the amount of radium emanation contained in the atmosphere 

 at any given altitude. In order to obtain results which would 

 give the variation for altitude alone, it would be necessary to 

 take observations from a balloon or other air craft, but the diffi- 

 culties of carrying out observations of long duration under such 

 conditions are practically unsurmountable. The only alternative 

 was to take observations on a high mountain peak as nearly 

 isolated as possible from surrounding peaks. In this case, 

 the effect of altitude is obtained only in so far as the air 

 currents are horizontal or descending rather than ascending. 

 That this condition is approximately realized during a consider- 

 able portion of each day is evident from a study of the movement 

 of clouds around a peak. Observations extending from late 

 afternoon to early morning should give a fairly accurate test 

 of the radium-emanation content of air which had not recently 

 been in close contact with the surface of the earth. 



After a careful survey of the available mountains of northern 

 Luzon, Mount Pauai, elevation 2,460 meters, was chosen as the 

 most suitable place on which to carry out a series of observa- 

 tions. Besides being the highest peak in the range, Mount Pauai 

 afforded a source of water sufficiently near the top to provide 

 the necessary water pressure for a good filter pump. The labor 

 of transporting a complete laboratory equipment for the experi- 

 ment over a distance of 90 kilometers from the nearest railway 

 station and obtaining practically identical conditions as those 

 existing in the well-equipped Bureau of Science laboratory of 

 Manila was no easy task, but the results obtained more than 

 repaid us for our trouble. 



The apparatus for the work and its arrangement was prac- 

 tically a duplicate of that which we have already described as in 

 use in Manila. However, one or two minor changes in the 

 apparatus were necessary. In order to obtain a constant stream 

 of air through the charcoal tubes, we were compelled to sub- 

 stitute a filter pump for the motor-driven oil pump. Under a 

 constant pressure of 5 meters of water, the filter pump enabled 

 us to obtain a flow of 1 liter of air per minute. The greatest 

 variation in the rate of flow, as indicated by sensitive water 

 manometers, was somewhat less than 1.5 per cent even for 



