OCEAN ATMOSPHERIC-ELECTRIC RESULTS 



above the top of the box. This rod was used for the re- 

 mainder of the cruise (fig. 16). For reduction of record- 

 ed volts to volts per meter for the two different collector 

 rods, two standardizations were made with the bent rod 

 and two with the vertical. These are discussed in detail 

 in another part of this volume (pp. 127-132). 



The Potential-Gradient Recorder. --The recorder, 

 manufactured by Gunther and Tegetmeyer, consisted of 

 a blfilar electrometer of WuU's design, a projection 

 microscope, and a recording box with driving clock at- 

 tached. (Two recorders were taken on the cruise, nos. 

 4946 and 4947; no. 4946 was used at the stern rail loca- 

 tion throughout, except for twelve days in August 1928). 

 The recorder, together with various items of control 

 and operating equipment (except batteries), was con- 

 tained in the weatherproof box, the front of which was 

 removable to permit inspection, testing, and adjustment 

 of the apparatus (fig. 12). The collector rod was sup- 

 ported in an amber insulator which was mounted in the 

 tube projecting from the top of the box. Within the tube, 

 above the amber insulator, was located an electric heat- 

 ing coil which served to keep the amber dry. The cur- 

 rent in this coil, supplied by the ship's power plant, was 

 regulated by a rheostat mounted in the wooden box. To 

 protect the heating coil and amber insulator from rain 

 and spray a metal "skirt" or cap was attached to the 

 collector rod just above the end of the tube. Within the 

 box, the inner end of the collector rod, projecting down 

 from the amber insulator, made connection with the fi- 

 bers of the electrometer. 



The Electrometer. --The Wulf bifilar electrometer 

 was equipped with an inner insulated case constructed in 

 one piece. The inner case had a terminal which project- 

 ed from one side of the outer case or housing, and the 

 case was connected to the housing when the small thread- 

 ed cap on the terminal was screwed against the housing. 

 Care had to be taken to insure that this cap was not 

 against the housing when an auxiliary potential was ap- 

 plied to the inner case, when the housing was grounded. 

 A grounding terminal was located on the bottom of the 

 housing. Each battery supplying the auxiliary potential 

 was provided with a protective resistance in its circuit-- 

 10,000 ohms or more for each 100 volts. 



The fibers of the electrometer were illuminated by 

 a 110-volt lamp which was operated from the power plant 

 of the ship. The desired degree of illumination was ob- 

 tained by moving the lamp up or down or rotating it in its 

 holder, or by adjusting a rheostat which was in the lamp 

 circuit. On one side of the electrometer housing, under 

 the microscope tube, there was an aperture covered by 

 a screw cap. When the electrometer was in use, a glass 

 tube or bulb half -filled with drying material such as 

 phosphorus pentoxide was fitted at the aperture, mounted 

 on a brass ferrule which replaced the screw cap. Anoth- 

 er tube or bulb of drying material was mounted at the 

 aperture in the side of the cap which protects the upper 

 amber insulator of the electrometer. Both drying units 

 are shown in figure 12. 



The Projection Microscope. --To obtain a good pho- 

 tographic record, the projection microscope was adjust- 

 ed as regards both focus of the fibers and symmetrical 

 placing of the scale in the microscope in relation to the 

 fiber positions. For focusing, a screw on the upper side 

 of the microscope barrel could be loosened to adjust the 

 position of the projecting lens; for symmetrical placing 

 of the scale, the adjustment was accomplished by sliding 

 the microscope mounting sidewise in its support on the 



side of the electrometer housing, after loosening a 

 clamping screw. 



The Recording Box and Driving Clock.--The driving 

 clock was mounted on one side of the recording box (not 

 seen in fig. 12), so connected as to rotate the lower of 

 two wooden rollers within the box. Unexposed photo- 

 graphic paper was placed on the upper roller, and the 

 clock-driven lower roUer wound up the exposed paper 

 during operation. 



The back of the recording box was made to slide up- 

 ward for insertion and removal of the photographic 

 paper. To insert paper, the upper wooden roller was 

 removed from the box by pulling out the upper knob 

 which was on the side of the recording box opposite from 

 the driving clock. The lower roller was removed by 

 pulling out the lower knob, when the exposed paper was 

 to be removed. Two cords, fastened in the recording 

 box above the upper roller, rested against the photo- 

 graphic paper and were kept taut by a weight which they 

 supported; the cords kept the paper in correct position 

 during operation. The moving paper was exposed as it 

 passed a slit on which was thrown the image of the elec- 

 trometer fibers and the scale. 



Photographic Paper. --Single weight matte enamel 

 bromide paper was used. It was supplied in rolls of 150 

 cm length and 67 mm width, which was sufficient for a 

 week's record and also allowed for a space between 

 daily records of 5 cm. The average hourly rate at which 

 the paper passed the slit when a week's record was al- 

 lowed to accumulate on the lower drum was 5.92 mm. 

 The first day required approximately 13.9 cm and the 

 last day 14.5 cm. 



Automatic Control of Time Marks. --The driving 

 clock on the side of the recorder box was equipped with 

 a contacting device which closed an electromagnet cir- 

 cuit once every hour for a period of two minutes, begin- 

 ning one minute before the hour and ending one minute 

 after. The electromagnet was mounted at an aperture 

 on the side of the cap covering the top of the electrome- 

 ter, and when actuated, its inner end attracted a flexible 

 metal strip which was groimded and which moved suffi- 

 ciently far to make contact with the post at the top of 

 the electrometer fiber system and to groimd it. The 

 hourly time-marks not only controlled the time record 

 but provided points for establishing a base line from 

 which deflections of the fibers during regular recording 

 could be measured. 



Electrometer Calibration and Sensitivity. --For cali- 

 bration of the potential-gradient recording apparatus, the 

 collector rod was removed. A calibration was made each 

 week, if weather conditions permitted. From batteries 

 brought on deck, potentials in steps of twenty or thirty 

 volts were applied between the grounded part of the ap- 

 paratus and the insulated fiber system, and the deflec- 

 tions of the fibers noted for each value of voltage (fig. 

 17). The calibrations usually covered the range from 

 to about 300 volts. As calibration curves for electrom- 

 eters of this type usually are not linear, particularly for 

 the smaller deflections, it was arranged that during re- 

 cording an auxiliary potential be used of such magnitude 

 and sign that the deflections would usually be in that 

 range of the scale having the best linearity. In this pref- 

 erable range the sensitivity in divisions per volt was 

 greater also, giving added reason for the use of the aux- 

 iliary potential. A value of auxiliary potential of 50 to 

 100 volts was usually used, and as the potential-gradient 

 of the atmosphere is positive with respect to earth in 



