262 CARNEGIE INSTITUTION OF WASHINGTON. 



leadership of Mr. O. G. Ricketson, to obtain the geographic positions of the 

 Maya ruins visited during March and April 1923. The requirements set 

 were (a) that values for latitude and for longitude be correct within one-half 

 mile, and (b), because of the difficult transportation conditions to be en- 

 countered through dense tropical vegetation and short time available, that 

 only the most portable instrumental outfits be carried. 



A theodolite-magnetometer with 101-mm. vertical and horizontal circles 

 of Department design and construction^ was used for the astronomical and 

 magnetic observations. Latitudes were determined from circummeridian 

 observations of the Sun and local mean times by morning and afternoon 

 observations of the Sun at as nearly equal altitudes as the time and conditions 

 at the stations permitted. (For detailed description of the methods of obser- 

 vation and reduction followed, see pp. 22-33 of volume I of the Researches of 

 the Department of Terrestrial Magnetism.) For determining the corrections 

 on standard time for the chronometers a long-wave wireless receiving-set of 

 the United States standard destroyer type was used with slight modification 

 necessary for its operation with dry-cell batteries. This set consisted of 

 receiver with load-coil to increase the receiving range (the range of wave- 

 lengths being 600 to 25,000 meters) , audion control-panel with one vacuum- 

 tube, and an amplifier with two vacuum-tubes. The tubes were Western 

 Electric type N, and the same ones were used throughout the field work. The 

 set-up of antenna, phosphor-bronze stranded cable, was varied to suit cir- 

 cumstances, trees serving usually as supports. The length was generally 

 200 feet, but frequently less, and for one set-up it was only 50 feet; the height 

 averaged about 50 feet. This equipment functioned excellently, and all 

 longitude determinations except for one station depend upon time-signals 

 received from either the Balboa or Arlington station, or both, before and 

 after local time observations. Trouble was experienced frequently with 

 static, but the signals were distinguishable despite this. 



That the desired accuracy for both latitude and longitude was obtained 

 is indicated by the plane-table traverse carried out by Mr. J. O. Kilmartin, 

 junior topographic engineer of the United States Geological Survey, between 

 Tayasal and Ixlu, in mapping Lake Peten. The agreement between plane- 

 table positions and those determined as above indicated was within about one- 

 quarter minute of arc. 



Observations for the magnetic elements were made when opportunity 

 offered. Examinations made, so far as the limited time available at each 

 station permitted, indicated that there had been no attempt to follow any 

 definite orientation when constructing the pyramids. El Cayo, British 

 Honduras, served as the base-station, and therefore the results obtained there 

 are included. (For details as to methods followed, see volumes I, II, and 

 IV of "Researches of the Department of Terrestrial Magnetism.") 



On the diurnal variation of the potential gradient of atmospheric electricity.^ S. J. Mauchly. 

 Terr. Mag., vol. 28, 61-81 (September 1923). 



Further results on the diurnal variation of the potential gradient of atmospheric electricity 

 from observations aboard the Carnegie, and comparisons between land and 

 ocean results.' S. J. Mauchly. Phys. Rev., vol. 21, 721-722 (June 1923). 



New observations obtained aboard the Carnegie during the year ending 

 November 1921 increased by 50 per cent the observational data regarding 

 the diurnal variation of the potential gradient over the oceans. A separate 



^ J. A. Fleming, Two new types of magnetometers made by the Department of Terrestrial 

 Magnetism of the Carnegie Institution of Washington, Terr. Mag., vol. 16, 1-12 (March 1911). 



* Presented before the Section of Terrestrial Magnetism and Electricity of the American 

 Geophysical Union, Wa.shington, April IS, 192.3. 



^ Presented before the American Physical Society, Washington, April 20, 1923. 



