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XIV. DISCUSSION OF THE OBSERVATIONS OF ATMOSPHERIC 



ELECTRICITY. 



BY 



C. T. R. WILSON, F.R.S. 



INTRODUCTORY NOTE BY L. C. BERNACGHI. 



OBSERVATIONS of atmospheric electricity with the Kelvin portable electrometer were made during 1902 

 and 1903. During the winter months these observations were often very unpleasant to take on account of 

 the small screws and bare parts of the small instrument, which could not be handled with mittened fingers. 

 For a polar climate some larger instrument, which does not necessitate the observer being frost-bitten 

 when using it in cold weather, should be employed, or some form of self-recording electrometer. 



The observations were taken on a stand about 4 feet above the rock surface, and away from any 

 buildings, erections, &c. During the dark months observations were taken at llh. a.m. and 5h. p.m. every 

 day, excepting when high winds with low temperatures made it impossible. After the return of the sun, 

 observations were generally taken every two hours from lOh. a.m. to lOh. p.m. The direction of the wind, 

 temperature, form of cloud, &c., was entered with the observation. 



From 8h. a.m. on November 22 to 3h. a.m. on November 25, 1902, a series of hourly observations were 

 carried out with the assistance of Engineer Commander R. W. SKELTON, R.N., chief engineer of the 

 "Discovery," and again in 1903 two-hourly observations from noon on October 7 to noon on October 10. 



Besides the two series of three days, observations were occasionally taken on individual days throughout 

 the twenty-four hours in both winter and summer. 



The observations during the second year are not so complete as during the first, but are supplemented 

 by observations taken at 15 feet above the ground, immediately after the observations at 4 feet; an 

 insulated wire from the burning match at the top of the pole to the instrument being employed for the 

 purpose. 



Whenever there was drifting snow in the air, or fine ice-needles, the difference of potential was very 

 large and variable, and in many cases the electrical strain would discharge the electrometer. 



The obeerrationB were carried out by Mr. L. BERNACCHI, except during his absence on a sledging 

 expedition from September 23 to October 2, 1902, when they were taken by Mr. E. W. SKELTON, R.N., 

 Chief Engineer of the "Discovery," who also assisted with the continuous series of observations of 

 November 22 to 25, 1902, and of October 7 to 10, 1903. 



The observations consisted of measurements of the electric potential at a definite height above the 

 ground. The electrometers originally supplied to the " Discovery " were two Thomson portable electro- 

 meters by White, and an Exner electroscope. The last-named, however, met with an accident on the 

 outward voyage and was never used. Of the portable electrometers one (No. 35) was only used on a 

 very few occasions, practically all the observations discussed below being taken with the other portable 

 electrometer (No. 81). 



