Dike — Recent Observations in Atmospheric Electricity. 207 



air and required 3/4 liter of liquid air for a three-hour run at 

 the rate of 1/2 liter of air per minute. The tests were very 

 similar to those in the absorption method, except that on 

 account of the large amount of liquid air required simultaneous 

 tests with the radium solution could not be made, so they had 

 to be alternated. A first series of seven measurements gave 

 140 XlO -12 grams of radium as the equivalent, and a second 

 series of three gave 90xl0~ 12 grams. A third series, using in 

 one case sulphuric acid and in another a freezing mixture as 

 dehydrators, gave 130 XlO" 1 ' 2 grams. 



Parallel tests made with the two methods — condenser and 

 charcoal — show the condenser to be rather more efficient than 

 the charcoal. It does not seem likely that the radium emana- 

 tion and its products in the air are responsible for anything 

 like all the natural ionization of the air. Eve, in Canada, has 

 used the charcoal absorption method of measuring the radium 

 equivalent per cubic meter and found as the mean of obser- 

 vations extending over a year 60 XlO -12 grams. The ratio of 

 the maximum to the minimum values found is seven to one. 

 Summer and winter values are about the same. Deep cyclones 

 with heavy rain cause increase while anti-cyclones cause a 

 decrease in the value. Ashman, working at the University of 

 Chicago, used the liquid air method, comparing the rate of dis- 

 charge produced by the emanation from a known volume of air 

 with that produced by the radiation from a portion of a mineral 

 containing a known amount of uranium, assuming the amount 

 of radium associated with one gram of uranium to be 5*4 xlO" 7 

 grams. 



The result of four tests gave as the radium equivalent 

 97 X 10 ~ 12 grams. Experiment showed that the coil condensed 

 all the emanation and that two similar coils in parallel gave 

 duplicate results. The highest value, 200 XlO" 12 grams, was 

 obtained after a heavy rain and general thaw following several 

 weeks of freezing weather with the ground covered with snow. 

 The activity curve of the emanation showed it to be identical 

 with that of radium. The values found by all three observers 

 are thus seen to be of the same order, and in as good agree- 

 ment as could be expected considering the variability -of the 

 quantity to be measured. 



G-erdien has made an elaborate study of the velocities of 

 the carriers of the emanation in the atmosphere, using the 

 trajectories of the particles carried by a uniform current 

 of air and acted upon by an electrical field about a cylindrical 

 conductor whose axis is parallel to the direction of the air cur- 

 rent, as a basis of computation. The deposit on the cylinder 

 was collected, and according to its distribution over the electrode 

 and according to its rate of decay was differentiated into car- 



