DEPARTMENT OF TERRESTRIAL MAGNETISM. 297 



Brazil Eclipse Expedition, 1919. — The program of the atmospheric- 

 electric observations made at Sobral during the total solar eclipse of 

 May 29, 1919, was prepared, together with the instructions, and the 

 required instrumental equipment was assembled and tested. A special 

 form of insulator to meet the tropical conditions of humidity and insect 

 life was designed for supporting the ionium collectors used in connec- 

 tion with the potential-gradient observations. This insulator was con- 

 structed in the Department's instrument shop and proved, in operation, 

 to be very satisfactory. 



Carnegie Atmospheric-Electric Work for Cruise VI, — A careful study 

 was made of the various official reports and correspondence relating 

 to the atmospheric-electric work of Cruises IV and V to secure a 

 proper basis for such modifications and repairs as could be made in the 

 available time. An attempt has been made to eliminate all avoidable 

 difficulties to the end that the observer should have more time and 

 energy to cope successfully with those difficulties which are inherent 

 and unavoidable. A great advance in this direction results from the 

 newly-installed storage battery, which furnishes the power for driving 

 the fans of the conductivity apparatus and the radioactive-content 

 apparatus. This will do away with the periodic renewal of the pri- 

 mary battery which has heretofore been necessary. 



It has long been felt that one of the most troublesome problems asso- 

 ciated with atmospheric-electric work on shipboard is that of suitable 

 potential batteries for the various instruments. This is especially true 

 where the observations between ports sometimes extend over several 

 months, as is the case on the Carnegie. For reasons which have been 

 pointed out by Swann {Researches Department Terrestrial Magnetism, 

 vol. Ill, p. 378), the Kriiger batteries have not been found very satis- 

 factory. Throughout most of Cruises IV and V batteries composed of 

 ordinary flashhght cells were used. These proved to be much superior 

 to batteries of the Kriiger type, but for the work under consideration 

 are open to two serious objections: (a) although the internal resistance 

 is initially low, it increases rather rapidly with age, thus introducing 

 the very difficulties which render the Kriiger type unsatisfactory; {h) 

 these batteries are constructed for use in flash-lights, and are therefore 

 not designed for longevity. Experience both aboard the Carnegie and 

 in the atmospheric-electric observatory at Washington has shown that, 

 owing to the corrosion of the zinc element of the battery from within, 

 very frequent renewals are required in order to have a satisfactory 

 service. As noted in the Director's annual report for 1918, page 239, 

 experiments have been in progress with batteries composed of chloride- 

 of-silver dry cells. These batteries have now given satisfactory service 

 for more than a year in the atmospheric-electric observatory at Wash- 

 ington, and were used with entire satisfaction in connection with the 

 atmospheric-electric observ^ations at Lakin last year and at Sobral 



