TRANSACTIONS OF SECTION A. 625 



that it is inverted, and to some extent dulled in brilliancy. If, however, the sur- 

 face of the clouds is irregular, such as those of the cumulus type, the image of the 

 flash will take the shape of the irregular surface. In this way a zig-zagged flash 

 with long angles could be formed very like the lightning flashes depicted by 

 artists. 



If there happen to be more openings than one in the clouds between the flash 

 and receiving surface, there will be a corresponding reduplication of the flashes, 

 which may perhaps explain some of the multiple effects observed. 



If projection flashes occur in nature it becomes a question whether the photo- 

 graphic plate can register them. 



2. Report on Solar Radiation. — See Reports, p. 81. 



3. Report on Earth Tremors. — See Reports, p. 184 



4. Reports on Earthquakes in Japan. — See Reports, pp. 81, 113. 



o. On some Experiments made with Lord Kelvin's Portable Electrometer. 

 By Abthur Schuster, F.R.S. 



Experiments made during a recent trip to Switzerland have demonstrated the 

 great convenience of Lord Kelvin's portable instrument for the observation of 

 atmospheric electricity. The electrometer can easily be carried in a knapsack to 

 almost any place the mountaineer can reach, and the observations are readily per- 

 formed in a short space of time. The object of the experiments was to learn, if 

 possible, whether the electric force at great heights is sensibly diff'erent from that 

 at the sea-level. But o'n'ing to the diiflculty of comparing together observations 

 made in valleys with those made on mountain peaks, the measurements made 

 during the past year were entirely of a tentative character, more for the purpose 

 of testing the working of the instrument than of obtaining any definite results. 

 The numbers given are only relative, and are referred to an arbitrary unit. 



Numerous experiments made in tine weather in the centre of a small meadow 

 in front of the hotel at Pontresina gave for the electric force, on the average, about 

 30, while the number obtained on September 13, in Ipswich, in a place rather more 

 sheltered by surrounding houses, was between 80 and 100.' 



On the so-called ' Diavolezza Pass ' the force was as high as 147 ; on the Isola 

 Pars, a rocky island, projecting well out of the surrounding glaciers, the number 

 found was 116. The instrument was taken on August 19 to the top of the Glii- 

 scheint (12,000 feet), which consists of a ridge of rocks just wide enough for one 

 man to stand upon. The electric force reached the number 816, while on the snow- 

 field a few hundred feet below the top, the force was only 170. The top of the 

 Schafberg gave 357. 



On the Morteratsch glacier the numbers were, as a rule, very low, except on one 

 occasion, when a strong downward wind was blowing ; even then the force was only 

 42. Half a mile below the foot of the glacier, the numbers were very irregular, 

 and seemed to depend a good deal on the direction of the wind. On one occasion, 

 ■when that direction was frequently changing, a negative electrification was ob- 

 served whenever the current of air was away from the glacier. This may have 

 been due to the negative electrification caused by the glacier stream in a way 

 similar to that in which a similar electrification is produced by a waterfall. 



The diurnal variation was observed on one day by taking measurements every 

 half-hour during the morning and every hour during the afternoon till seven 

 o'clock. A maximum of 36 was observed at 11 a.m. The numbers then fell 



' In Mnnchester, during the fine weather in the last fortnight of SeiDtember, the 

 nnnibors went up to 250. 



1^0.'). SS 



