VII. ATMOSPHERIC POTE NTIA L - GR ADIE NT RESULTS 



EXPLANATORY NOTES AND COMMENTS 



Section Vn contains hourly mean values, on Green- 

 wich Mean Time, of the atmospheric potential-gradient 

 expressed in volts per meter. These values in volts per 

 meter have been obtained from values of volts recorded 

 at the stern rail of the ship with Gunther and Tegetmeyer 

 recorder No. 4946 or 4947, by the use of appropriate re- 

 duction factors. For the period from August 10, 1928, to 

 October 11, 1928, the factor 0.7 was used for all main- 

 sail and boom positions, whereas for the period Novem- 

 ber 6, 1928, to November 18, 1929, the factors 2.9, 3.2, 

 and 3.7 were used for port, starboard, and crutch posi- 

 tions, respectively, of the boom with the mainsail up or 

 down. The cause for the change in factors between Oc- 

 tober 11 and November 6, 1928 already has been dis- 

 cussed in the section devoted to instruments. 



Between August 7, 1928 and November 18, 1929 the 

 ship was at sea for 317 days. The photographic record 

 of potential gradient was lost or was unusable on 50 of 

 these days, and on 86 additional days record was ob- 

 tained for only part of the twenty-four-hour period, 

 owing to instrumental difficulties or bad weather. Com- 

 plete days totaling 181 have been tabulated in the present 

 table, and all available values for the 86 partial days. 



Instrumental Difficulties. --Instrumental difficulties 

 responsible for the loss of photographic record which 

 were most frequently encountered were as follows: 1. 

 Defective insulation; 2. Hourly zero-marks not record- 

 ed; 3. Photographic record unreadable because of inad- 

 equate illumination; 4. Electrometer fibers moving too 

 rapidly to make a legible record during disturbed weath- 

 er conditions; 5. Lens of electrometer telescope loose 

 and record illegible; 6. Recorder lamp burned out; 7. 

 Recorder drum not rotating; 8. Apparatus shut down for 

 repair or adjustment. 



Other less frequent difficulties which caused loss of 

 record were: 1. Photographic paper exhausted; 2. Pho- 

 tographic paper fogged; 3. Collector rod displaced by 

 wind (applies only August to October, 1928); 4. Sensi- 

 tivity of electrometer uncertain; 5. Defective auxiliary- 

 potential batteries making recorded values uncertain. 



Interpolated Values. --Interpolated hourly values 

 have been placed in brackets. Values have been interpo- 

 lated for periods of one to three hours only on days re- 

 garded as particularly quiet and undisturbed. No inter- 

 polating has been done over periods of bad weather. 



Electric Character. --Electric character-figures are 

 tabulated for all days for which these figures can be de- 

 termined. The character-figure is intended to indicate 

 the degree of disturbance on any day, but actually it in- 

 dicates only the duration of negative potential. Three 

 figures are used as follows: 



= A day with no negative potential-gradient 



1 = A day with an aggregate of two hours of negative 



potential or less 



2 = A day with an aggregate of more than two hours 



of negative potential 



Because negative potentials are encountered in disturbed 

 weather, and disturbed weather generally causes large 

 and rapid fluctuations in potential- gradient which often 

 make the record illegible, on some disturbed days there 

 is uncertainty sometimes as to whether the character- 



figure should be 1 or 2. In such cases both figures are 

 given, as 1-2. It must be emphasized that very disturbed 

 days are encountered which show high and variable posi- 

 tive values and no negative potential-gradient; these are 

 "zero" days as well as the very quiet days on which only 

 small variations are seen, and the system of characteri- 

 zation therefore does not cover the entire range of dis- 

 turbed conditions. Notably, there were many days in 

 July 1929 when fog, mist, or haze, and possibly very light 

 rain, occurred and yet no negative potential-gradient was 

 recorded, while extremely high positive values existed 

 for long intervals. Although classified as "zero" days, 

 these days belong in the category of very disturbed days. 

 Sail and Boom Position. --It will be noted that the 

 position of the mainsail and boom has not been tabulated 

 for the months of August to October, 1928. During this 

 period the bent collector rod was used on the potential- 

 gradient recorder and reduction-factor determinations 

 indicated that the recorded values of potential-gradient 

 did not change significantly with change in the sail and 

 boom position. After the short straight collector rod 

 was adopted on November 6, 1929, the boom and sail po- 

 sition became significant, and the present table includes 

 a symbol for each day thereafter. The symbols have the 

 following meanings: 



P = Mainsail up and boom to port 

 S = Mainsail up and boom to starboard 

 C = Mainsail down and boom in port crutch 

 D = Day divided into several intervals for which dif- 

 ferent positions were used 



Mean Dailv Value of Potential-Gradient. --After care- 

 ful inspection of the photographic records of potential- 

 gradient and the study of weather notes, certain days 

 were selected from the complete days as typical of the 

 least disturbed, fair-weather conditions encountered on 

 the cruise. There were eighty-two such days, and the 

 mean value for each of these days has been tabulated. 



Remarks. --Under this heading note is made of vari- 

 ous conditions affecting the potential-gradient, such as 

 bad weather and running of the main engine. The occur- 

 rence of negative potential is noted in every case. When 

 certain hours on certain days are disturbed and no ex- 

 planation can be found, the word "disturbed" is inserted, 

 with the time of the disturbed period. For the weather 

 notes the same symbols have been employed as were uti- 

 lized for sec. V, and the explanations for the various sym- 

 bols will not be repeated here. In the interpretation of the 

 notes, the punctuation is significant. Where two parts of 

 a note are separated by a comma, the events described 

 are concurrent. For example, "rain, neg.PG 10-12h," 

 indicates that both rain and negative potential-gradient oc- 

 curred between 10 and 12 hours. When the note reads 

 "rain; neg. PG 10-12h," where the semicolon replaces the 

 comma, the indication is that rain occur red at various other 

 times than 10 to 12 hours, as well as during that period. 

 The semicolon is used throughout where the events are not 

 completely simultaneous in the time. The exact periods 

 during which negative potentials prevailed are not given 

 in the notes, because the method of recording caused 

 some uncertainty as to the extent of these periods; only 

 the hours in which negative potentials occurred are noted. 



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