234 CARNEGIE INSTITUTION OF WASHINGTON. 



A large and important part of the computational work involved in the 

 above reductions was performed by Mr. C. C. Ennis and Miss Mary C. 

 Parker. 



Polar-light investigations. — Preliminary studies bearing on this subject 

 have been continued, including the preparation of a report presented at the 

 annual meeting of the American Geophysical Union, April 1923. 



Progress in earth-current work} — Investigation of the nature and causes 

 of certain "spurious" potentials, or "plate effects," which often enter earth- 

 current measurements, was continued this year in the hope of finding means 

 of diminishing or eliminating this serious obstacle which lies in the way to 

 absolute measurement of earth currents. In connection with this work a 

 method was found of determining quantitatively the contact resistance of 

 individual earthed electrodes (see abstract, pp. 258-259). 



The recording instrument designed for use at Watheroo was delivered 

 by the makers in February and was given numerous tests at Washington 

 before sending to Watheroo for installation. As a part of these tests, the 

 instrument was set up at the Cheltenham Magnetic Observatory, where a 

 continuous record was obtained for three days on short earth-current lines. 

 This, besides serving as a further test, would, it was believed, give information 

 as to whether leakage currents from electric railways are of such magnitude 

 at Cheltenham as to exclude the possibility of making measurements of 

 true earth currents there. The records obtained, however, show no con- 

 clusive evidence of such an effect. 



A system was developed for reducing such earth-current records as are 

 obtained with this recorder, and with the effective assistance of Mr. Ennis 

 the three days of Cheltenham records were reduced and analyzed. A chart 

 was designed, by which the azimuth and magnitude of the earth-current 

 potential-gradient could be found from scaled values (or their departures 

 from a mean value) by a single entry. 



Preparation of equipment for the resistivity surveys which are to be made 

 in connection with the Department's earth-current lines is under way, and 

 it is hoped this will be ready for field tests by the end of the present calendar 

 year. 



The system for earth-current potential measurements at Watheroo is now 

 furnishing preliminary records. For a description of this sytem, see abstract 

 on page 258. The lines are equipped, however, with only temporary elec- 

 trodes; the recommendation of a type suitable for permanent installation must 

 await the results of some incomplete investigations. 



OBSERVATIONAL AND ADMINISTRATIVE WORK. 



The Division of Observational and Administrative Work continued in 

 charge of the Assistant Director. Good progress was made in the field and 

 office work and in the development of the program for observatory work. 

 In the administrative work principal assistance was received from the chief 

 clerk, Mr. M. B. Smith, and from the property clerk, Mr. J. J. Capello. 



A bulletin containing information and news regarding personnel, observa- 

 tory work, field operations, and other items of interest was issued to members 

 of the staff on the average once a month, beginning the end of April. 



^ From subreport by O. H. Gish, associate physicist. 



