304 CARNEGIE INSTITUTION OF WASHINGTON. 



easy removal of all parts requiring occasional inspection and cleaning. 

 Furthermore, all parts are of standard dimensions to expedite repairs and 

 replacements. The arrangement of the recording drums is such that the 

 approximate value of a given element may be determined at any time. The 

 fans which draw the air through the conductivity apparatus are driven by 

 small electric motors operated on 32 volts from storage batteries. Electric 

 recording lamps are also used. The batteries, generator, and gasoline motor 

 are separately housed far enough away from the atmospheric-electric house 

 to prevent any disturbance from fumes. 



The essentials of the building designed by Mr. Fleming for the installa- 

 tion of the atmospheric-electric apparatus, to be described in greater detail 

 elsewhere, include (a) substantial and rigid construction to eliminate deleteri- 

 ous vibration effects from operating motors, (6) moderate temperature ranges 

 in the observing room without artificial temperature control, (c) arrange- 

 ments such that the air passed through the air-flow tubes of the aspiration 

 apparatus shall be exhausted outside of the building in such a manner as to 

 prevent its again entering the apparatus, (d) arrangements for properly 

 grounding the entire outer surface of the building, and (e) provision of ample 

 floor space for installation of apparatus for the atmospheric-electric elements 

 referred to above and for additional installations for atmospheric-electric and 

 earth-current equipment. 



These requirements are met by the use of reinforced concrete. The record- 

 ing room is 3.7 by 5.5 by 2.1 meters (12 by 18 by 7 feet) inside dimensions, 

 with double walls and double roof (5-cm. continuous air-spaces between) 

 and heavy concrete floor built 0.4 meter above a concrete slab at ground-level. 

 The building is provided with a louvered wooden wall on three sides 0.5 

 meter from the concrete walls; on the fourth side this louvered wall is about 

 1 meter distant from the concrete walls of the building to provide suitable 

 entry to the observatory and a small room for necessary laboratory and 

 repair work, as well as for the storage of photographic paper, etc. 



Atmospheric electricity: Preliminary report on the diurnal and annual variations of the 

 potential gradient from observations at Washington, D. C., during 1918. 

 S. J. Mauchly. 



The Department of Terrestrial Magnetism has, since 1916, maintained an 

 experimental atmospheric-electric observatory on the deck of its Laboratory 

 in Washington. Although primarily for experimental and instructional pur- 

 poses, it has been possible also to obtain continuous photographic records of 

 the variations of the potential gradient, as indicated by a quadrant electro- 

 meter connected with an insulated ionium collector, for nearly the entire time 

 since January 1917. The observatory is located several miles to the north- 

 west of the city proper and surrounded mainly by second-growth woodland 

 with occasional clearings. While the site is not ideal for the location of a 

 permanent observatory, it has seemed desirable to make a reduction of the 

 records obtained, since they constitute the longest series of continuous records 

 of the potential gradient which have thus far been obtained in North America. 



The reductions under way include all the records obtained, but the remarks 

 which follow refer only to results derived from daily records free from negative 

 potentials and complete for 24 consecutive hours beginning at midnight, 75th 

 meridian mean standard time. The results are for recorded potentials only, 

 no account having been taken of the factor for reducing to absolute values 

 in volts per meter, and its possible diurnal and annual variations. On the 

 assumption that the variations of the potential gradient are essentially the 

 same as the variations of the recorded potentials, the results for 1918 may be 

 briefly stated as follows : 



