DEPARTMENT OF TERRESTRIAL MAGNETISM. 317 



ments of the potential-gradient, measurements of the penetrating radi- 

 ation, measurements of the radioactive content of the atmosphere^ 

 and meteorological observations. In the choice of the measurements, 

 and of the way in which they are taken, special attention has been 

 given to arranging matters so that the quantities shall be related to 

 one another in as definite a way as possible. 



At Washington studies have been carried out relating to the origin 

 and maintenance of the Earth's negative charge, and to the develop- 

 ment of satisfactory instruments for continuously recording the atmos- 

 pheric-electric elements at fixed stations. 



The Carnegie observations obtained during the cruise of 1914 have 

 been discussed by Dr. Swann (see abstract, pp. 337-342), and the obser- 

 vations on the current cruise are reduced as soon as possible after being 

 received. For further details, reference must be made to the abstracts. 



INSTRUMENTAL WORK. 



The instruments, constructed practically entirely in the Department's 

 instrument shop, comprised 2 magnetometers with theodolites, an 

 earth inductor, 3 special galvanometers, and the whole of the instru- 

 mental equipment for the atmospheric-electric work on the Carnegie, 

 consisting of the apparatus for the measurement of potential-gradient, 

 atmospheric conductivity, ionic numbers, penetrating radiation, and 

 radioactive content of the atmosphere. Furthermore, 5 quartz-fiber 

 electroscopes have been constructed, also 1 conductivity apparatus for 

 land observatory use, several 100-volt batteries of cells, apparatus for 

 the production of high and steady potentials, photographic apparatus for 

 recording ship's motions, and miscellaneous experimental appliances. 

 Progress has also been made on the construction of a new deflector for 

 determining the magnetic declination and the horizontal intensity at sea. 



The difficulty experienced in procuring brass and bronze devoid of 

 magnetic impurities has been so serious as to compel the Department 

 to consider the estabUshment of a small foundry of its own ; preliminary 

 arrangements to this end have been made. 



DETAILS OF OBSERVATIONAL WORK. 



OCEAN WORK. 



At the close of the fiscal year 1914 the Carnegie lay in Beard's Yacht 

 Basin at Brooklyn, New York. Immediately afterwards the vessel 

 was laid up in ordinary. Plans were prepared for the construction of 

 an observatory just abaft the after dome for the housing of the new 

 instruments used in the atmospheric-electric observations, and for an 

 additional stateroom on the starboard side of the cabin; also for a belt 

 of brass plates as a protection against ice. On January 12 the Carnegie 

 was taken over to the Tietjen & Lang Dry Dock Company in Hoboken 

 to have these plans executed, and also to have the vessel's bottom 

 sheathed with a copper alloy for tropical waters. The work was sup- 

 ervised by the firm of Gielow and Orr and by our representative^ 



