3U8 ATMOSPHERIC ELECTRICITY. 



reversal of the potential gi'adient. In this case the changes in the potential 

 were comparatively regular, there being few of the rapid changes which generally 

 accompanied the reversed potential, 

 (i) October 2, 1911. — There was a heavy blizzard on this day with much new snow 

 and drift. It was impossible to prevent the insulators becoming covered with 

 snow, therefore the record is doubtful ; but for several hours between 4 

 A.M. and 9 A.M. the needle was frequently on the negative side of the zero, 

 therefore it is almost certain that duiing this period the potential was 

 negative. 



(5) November 6, 1911. — This was another day with a high southerly wind between 30 

 and 40 miles an hour. Until 9 a.m. there was some surface drift and the 

 potential as usual was positive and high. The drift then ceased, but the wind 

 continued, and the potential steadily decreased to zero at about 3 p. m. and then 

 became negative for about 40 minutes, after which it became positive again. 

 The clouds were heavy and low throughout the day. 



(G) December 8, 1911. — This is the most instructive case. Two days previously there 

 had been the greatest snowfall of the year, which had been in the unusual 

 form of large flakes. The whole of the frozen Sound was covered with about 

 18 inches of light loose siaow. At 1 p.m. a high wind from the north .sprang 

 up driving the loose snow before it. The potential at first was high and positive, 

 then at 4 p.m. it commenced to fall rapidly, at 6 p.m. it had become negative 

 and the needle of the electrometer had swung to its extreme negative position 

 where it remained with a few short breaks until 11 p.m. There is no doubt 

 that during this period high negative potential occurred and it was the longest 

 period of continuous reversed gradient recorded. Throughout the whole period 

 of negative gradient the sky was clear, but there was a very heavy surface 

 drift of light snow caused by the high wind. The drift, however, was not higher 

 than about 3 or 4 feet, above which the air was quite clear. The whole of 

 the drifting snow was therefore well below the collector. 



(7) December 9, 1911. — The high wind of the previous day continued, but when it had 



removed the upper layer of soft loose snow the drift decreased and none was 

 reported after 8 a.m. 



On the whole the potential was high and positive, but it was most irregular, the 

 needle of the electrometer constantly swinging to, and occasionally across, the 

 zero. Between 10 a.m. and 1 p.m. the conditions were reversed, for then the 

 potential was negative and high with occasional swings to the positive side. 

 Afterwards the potential returned to the positive side and remained high until 

 the wind dropped, when it became normal. In this case we have an unsteady 

 potential and a long period of negative potential with little or no drift, but 

 again a high wind. 



(8) December 30, 1911. — Throughout this day there was a moderate wind 20 — 30 miles 



an hour from the E.S.E. with snow and drift. The potential was very low all 

 day and was sometimes positive and sometimes negative. The record is almost 

 exactly like one obtaiired on a rainy day in temperate regions. The temperature 

 was between 20° and 25" F. 



(9) Febriuiry 10, 1912.— Between 3 pm. and 4 p.m. a little snow fell and the potential 



gradient became negative for about half an hour. There was a light wind 



