OCEAN ATMOSPHERIC -ELECTRIC RESULTS 



used for conductivity measurements from the beginning 

 of cruise VII in May 1928, until the ship arrived at San 

 Francisco at the end of July 1929. While in port at San 

 Francisco, recording apparatus was installed and con- 

 tinuous records of conductivity were obtained for the 

 three months September to November 1929- -the remain- 

 der of the cruise. Positive and negative conductivity 

 were recorded on alternate days, so approximately equal 

 amounts of data were collected for each sign (fig. 9). 



In addition to the measurements made in the observ- 

 ing cabin, of conductivity, ion content, penetrating radi- 

 ation, and radioactive content, measurements of poten- 

 tial-gradient were made at the stern rail as on previous 

 cruises. Eye-reading observations were made with po- 

 tential-gradient apparatus 2 from the beginning of the 

 cruise in May 1928, until September 16, 1928 (fig. 10). 

 Continuous recording of the potential-gradient was begun 

 on the stern rail July 7, 1928, after imsuccessful at- 

 tempts to record at the top of the mainmast and on the 

 roof of the atmospheric-electric observing cabin (fig. 

 11). The recording apparatus employed four ionium - 

 coated collectors mounted at the tip of an insulated col- 

 lector rod, the latter being attached to the fiber system 

 of one of two recording electrometers designated Gun- 

 ther and Tegetmeyer 4946 or 4947 (fig. 12). Recording 

 of potential- gradient with this apparatus was continued 

 on the stern rail to the end of the cruise in November 

 1929. A considerable number of parallel observations 

 of potential-gradient with eye-reading and recording 

 equipment was obtained between July 7 and September 

 16. 



Measurements of the concentration of condensation 

 nuclei in the air were added to the program of atmos- 

 pheric-electric observations for cruise VII. A small 

 portable nuclei counter (figs. 13, 14) of the type devised 

 by John Aitken in 1890 (2) was used, the measurements 

 being made on the ship's bridge. Nuclei counter 4 was 

 employed for the initial part of cruise Vn, but difficul- 

 ties with it, arising from accidents, required its re- 

 placement. It was used until arrival at Callao, Peru, 

 January 14, 1929, but during the stay at Callao, counter 

 5 was obtained from the Department's Huancayo Mag- 

 netic Observatory at Huancayo, Peru, and was used for 

 the remainder of the cruise. 



From the above brief summary the following list of 

 apparatus for the measurements of the atmospheric- 

 electric elements on cruise vn may be made. 



Ion counter 1 



Penetrating radiation apparatus 1 



Penetrating radiation apparatus 5503 (from 



July 7, 1928) 

 Radioactive content apparatus 4 

 Conductivity apparatus 8A (eye-reading to July 



28, 1929; recording from September 3, 1929 to 



to November 18, 1929) 

 Potential-gradient apparatus 2 (to September 



16, 1928) 

 Potential-gradient recorder 4946 (from July 7, 



1928 to November 18, 1929, except twelve 



days in August 1928 when 4947 was used) 

 Nuclei counter 4 (to January 14, 1929, then 



counter 5 to November 18, 1929) 



In the following paragraphs the various types of ap- 

 paratus will be described in sxifficient detail to give the 

 reader a background of information to assist in evalu- 

 ating for himself the data presented later and the dis- 

 cussions which complete the volume. Much of the 



descriptive material was presented by W. F. G. Swarm 

 in connection with his preliminary discussions of the 

 results of cruise VI (3), but is repeated here for conven- 

 ient reference. 



Potential-Gradient Apparatus 2. - -This apparatus is 

 shown in use in figure 10. A brass tube was attached at 

 one end to an axle so that it could rotate about that axle. 

 The axle was mounted on supports fixed to a platform 

 located at the mid-point of the stern rail, and the brass 

 tube carried at its projecting end an umbrella-shaped 

 conductor made of fine mesh bronze screen. The handle 

 by which the tube was rotated was insulated from the rod 

 and axle, and the latter was insulated from earth by sul- 

 phur rings at each end which were fixed in the axle sup- 

 ports. The axle was connected by a thin wire to the in- 

 sulated fiber system of bifilar electrometer no. 28, used 

 for this work exclusively. A contact was provided such 

 that when the umbrella- shaped conductor was hanging 

 downward over the stern at its lowest position the elec- 

 trometer fibers were earthed. On rotating the conductor 

 to some higher position as fixed by a stop, a deflection 

 proportional to the potential-gradient was obtained on the 

 electrometer. Insulation difficulties were minimized by 

 this arrangement, since the leak occurring in the brief 

 time required for turning the conductor from one posi- 

 tion to the other would be very small. Further, the op- 

 eration could be performed so quickly that a reading 

 could be obtained at any desired position of tUt of the 

 ship. The sensitivity of the apparatus was considerable, 

 and it was not difficult to arrange to get full-scale de- 

 flection for normal values of potential-gradient. The 

 brass tube and umbrella- shaped conductor could be put 

 in place or removed very quickly, and when the appara- 

 tus was not in use these were removed and the electrom- 

 eter and axle were covered by a weatherproof box. Aux- 

 iliary potentials for the inner case of the electrometer 

 were supplied from batteries stored in a small labora- 

 tory forward of the quarter-deck, the connecting wires 

 being brought beneath the deck to a marine plug located 

 conveniently near the apparatus. With such an auxiliary 

 potential, the range of the instrument could be adjusted 

 to suit the occasion, and further, the sign of the prevail- 

 ing potential-gradient could be determined readily by 

 noting the direction of movement of the deflected fibers 

 when a small change was made in the potential of known 

 sign applied to the inner case. 



Procedure for Observations with Apparatus 2 



1. Uncover the electrometer and axle; attach the 

 brass tube and the umbrella- shaped conductor. 



2. Examine the electrometer and axle for excessive 

 dampness of insulators or for any foreign material that 

 may be bridging across insulators. 



3. Test for insulation leak. To do this raise and 

 lower the umbrella several times. Note the response of 

 the fibers of the electrometer to each raising. If there 

 is no response, the insulation breakdown is complete. If 

 the fibers return immediately to zero reading, the leak 

 is comparatively large. If the maximum deflection is 

 maintained sufficiently long so that the fiber readings 

 may be noted in an unhurried manner, the insulation is 

 satisfactory. Poor or bad insulation must be remedied 

 by drying or cleaning the insulators. 



4. Having satisfactory insulation, apply to the inner 

 case of the electrometer auxiliary potential of such 

 magnitude as to bring the deflections of the fibers with 

 the umbrella raised to a position on the scale most con- 

 venient for rapid reading. 



5. With the fibers earthed (umbrella down) observe 



