( 583 ) 



XXXI. — Observations on Atmospheric Electricity. By C. Michie Smith. 



(PI. CXLVI.) 



(Read June 1st, 1885.) 



The following observations on atmospheric electricity were made on the top 

 of Dodabetta, between 3rd and 12th January 1885. The position of the 

 electrometer, when not otherwise stated, was at a height of about 5 feet above 

 what remains of the walls of the bungalow formerly used as a meteorological 

 observatory. Dodabetta is the highest hill in the Neilgherries, and the bunga- 

 low was built exactly on the top, which is in latitude 11° 24' 5"*40 N., longitude 

 76° 46' 44"39 E., and at a height of 8642 feet above mean sea-level. The top 

 is free from trees, and my tents were slightly below, and at a sufficient distance 

 off to prevent them interfering in any way with the accuracy of the readings. 



The rainfall at the end of 1884 was unusually heavy, and continued till near 

 the end of December, so that mists were very frequent in the afternoons and 

 evenings. These mists usually collected over the hollow in which Coonoor and 

 Wellington are situated, and gradually spread round Dodabetta from about E. 

 by N. to W., and at times remained for hours as a sea of mist, with a nearly 

 horizontal, though of course wavy, upper surface, which reached to within a 

 few hundred feet of the top of the mountain. At times portions would be 

 blown off from the surface of this sea, and would reach the hill-top; but usually, 

 during the day, any mist that reached the top dissolved almost instantly on 

 reaching the warmer air rising up the north-west face of the hill from the valley 

 in which Ootacamund lies. Occasionally, however, the top was completely 

 enveloped in mist, and it was impossible to judge with certainty whether it was 

 a condensing or a dissipating one. Unfortunately I had no hygrometer with me ; 

 for, knowing the difficulty of making any satisfactory shade. I thought there was 

 no use of taking one. It is, however, worth noticing that the mists after sunset 

 were, as a rule, very wetting, and were therefore probably condensing. 



Turning now to the observations, these are interesting in two ways. First, 

 as regards the daily range and period of maximum strength ; and, second, as 

 regards the influence of mist. As it was impossible to carry on observations 

 all night without an assistant, I confined myself to an attempt to get a fairly 

 complete series of readings between 7 h and 20 h (Madras mean time, reckoned 

 from midnight). On half the days readings were taken up to 22 h , and on 

 one night to 24 h . From 6th to 12th January the readings were, with 

 two exceptions, taken hourly from 7 h to 20 h , and a number of intermediate 

 readings were taken, when, owing to the presence of mist or from other cir- 

 cumstances, it seemed likely that they would be of value. In all, above 150 

 observations were made. The morning readings from 7 h to 13 h were little dis- 

 turbed by mists, except on the 8th, and the readings for these hours agree 



VOL. XXXII. PART III. 5 D 



