Atmospheric-Electric Observations, 1915-16 377 



The design of the methods of measurement and the organization of the scheme of pro- 

 cedure in the atmospheric-electric work were initiated by W. F. G. Swann. In the work 

 connected with the installation of the instruments aboard, and in the experimental work 

 prior thereto, he was assisted by S. J. Mauchly and H. F. Johnston, the observer to whom 

 had been assigned the atmospheric-electric work on the cruise. Swann and Mauchly 

 accompanied the vessel from Brooklyn as far as Gardiners Bay, in order to complete the 

 installations and tests of the new instruments. Mauchly continued with the Carnegie 

 as far as Balboa to complete the remaining adjustments found necessary. 



The observations from New York to Colon were made by Mauchly and Johnston. 

 From Balboa (April 12, 1915) until the return of the vessel to Lyttelton, New Zealand, on 

 April 1, 1916, after her sub- Antarctic circumnavigation cruise, they were made by Observers 

 H. F. Johnston and I. A. Luke, and at the present time Observers B. Jones and I. A. Luke 

 are carrying on the work. 



The following account by Swann contains a description of the instruments and methods 

 employed in the atmospheric-electric work, and a compilation and discussion of the data 

 submitted in the reports of Mauchly and Johnston through March 1916. 



ATMOSPHERIC-ELECTRIC QUANTITIES MEASURED. 



In the choice of quantities to be recorded in any extensive series of atmospheric-electric 

 measurements on the ocean, we must be guided by two main considerations. In the first 

 place, the quantities should be such that, taken together, they form as complete a whole as 

 possible. If we wish to discuss the variation of some quantity, such for example as the 

 atmospheric conductivity, tliroughout the day, in order to compare the results with land 

 values, it is desirable that we shall not omit to measure any quantity which we know to 

 be a controlling factor in the determination of this element. Secondly, it is necessary that 

 the quantities measured shall be such as can be obtained by apparatus which is adaptable to 

 ocean conditions. 



The atmospheric-electric quantities at present measured on the Carnegie are the 



following : 



(1) The potential-gradient A'. 



(2) The conductivities (X+ and X_) arising from the positive and negative ions. 



(3) The numbers (n+ and n_) of positive and negative ions per cubic centimeter. 



(4) The number of pau-s of ions produced per cubic centimeter per second in a closed 

 vessel (the penetrating radiation). 



(5) The radioactive content of the atmosphere. 



(6) The radioactive content of the sea-water. 



The meteorological observations which are made are : pressure, temperature, humid- 

 ity, extent and nature of clouds, and strength of wind and its direction. 



The diurnal variations of the potential-gradient, ionic-content, and penetrating radia- 

 tion are also under investigation. 



The conductivities are related to the numbers of ions per cubic centimeter by the 

 expressions X+ = n+er+, and X_ = n_e?;_, where e is the electronic charge, and v+ and v_ are 

 the velocities under unit field, of the positive and negative ions respectively. Since 

 X+/ft+e = y+ and X^/n_e = v_, measurements of X+ and X_, n+ and n_ lead directly to the 

 determinations of v+ and v_. 



The simultaneous measurement of conductivity and potential-gradient enables us to 

 calculate, if we wish, the value of the vertical conduction current-density, which is 



i=(X++X_)X 



The primary interest attaching to the measurements of the radioactive content and of 

 the number of pairs of ions produced per cubic centimeter inside a closed vessel lies in the 



