300 CARNEGIE INSTITUTION OF WASHINGTON. 



at sea will be of a higher accuracy than was possible with the moving- 

 coil galvanometer. 



The experience obtained during the last cruise of the Carnegie with 

 the atmospheric-electric instruments indicated as desirable certain 

 improvements and modifications in the instruments, and the sub- 

 stitution of a more reUable source of potential than the dry cells here- 

 tofore used. After a careful study by Dr. Mauchly of the various 

 reports made on atmospheric-electric work from time to time by the 

 Carnegie observers, suggested modifications in design were undertaken 

 in the instrument shop. The following instruments were overhauled 

 and practically rebuilt, numerous improvements and modifications 

 being effected in each case: potential-gradient apparatus No. 2, ionic- 

 content apparatus No. 1, penetrating-radiation apparatus No. 1, 

 radioactive-content apparatus No, 4, and conductivity apparatus No. 3. 

 The experience with silver-chloride cells in the atmospheric-electric 

 observatory at Washington and in the field at Sobral during the 

 special eclipse observations in May and June 1919, was so satisfactory 

 that it was decided to supply such cells for the Carnegie work. Batteries 

 in units of 50 cells with resistance of about 10,000 ohms in circuit, all 

 embedded in paraffin and suitably mounted, were made up. Assistance 

 was rendered in the installation of the atmospheric-electric instruments, 

 the magnetic instruments, and the various gimbal stands and other 

 appurtenances before the initiation of the Carnegie's cruise. 



Miscellaneous new work included the following : Partial construction 

 of sine galvanometer No. 1 for the absolute determination of horizontal 

 intensity; 18 magnetogram scaling-glasses; extensions to switch- 

 boards in the main laboratory for 14 two- wire and 3 three- wire special 

 direct-current and alternating-current circuits to the experiment 

 building; construction of the special switch-boards for the experiment 

 building ; construction of special Helmholtz-Gaugain coils with mount- 

 ing for varying horizontal-intensity fields when calibrating magnetic- 

 intensity instruments; the design and construction of special switch- 

 board for storage-battery electrical equipment on board the Carnegie; 

 and special instruments and apparatus in connection with military 

 work. 



The repair work, in addition to that on instruments referred to above, 

 included either remaking or extensive repairs on the following: mag- 

 netometers Nos. 1, 10, 14, 24, 25, 28; dip circles Nos. 189, 202, 242; 

 marine earth-inductor No. 3; deflectors Nos. 4 and 5; reversible gimbal- 

 stand; 12 sextants and one prismatic circle; mercurial barometers Nos. 

 3948, 4177; 3 thermographs and 1 barograph; motion-picture camera; 

 and other numerous small instruments and appurtenances for the 

 Carnegie. The machine-tool equipment was kept in order and repaired, 

 and was increased by the installation of a wet and dry grinder, a large 

 drill-press, and a tuyere and blower. 



