12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IIO 



figure for the number of molecules per cubic centimeter at sea level, 

 I compute that the number of molecules in a column of air of i square 

 centimeter cross section above Montezuma is approximately 1.4 x 10^^. 

 If there are 0.023 times as many ions in the ionic showers accompany- 

 ing average severe magnetic storms, it follows that the average in- 

 crease of density in ions per cubic centimeter in space between the earth 



, ^, ... 1.4x10-^X0.023 ,. 



and the sun on such occasions is — ~ r:, — ^=2x10 , or 10 



15x10^2 



times the number of the earth's inhabitants, approximately. On March 



23, 1920, the figure was approximately 10 times larger still. 



