Prof. W. Thomson's Notes on Atmospheric Electricity. 3G1 



College Tower of the University of Glasgow. A divided ring- 

 electrometer was used at the last-mentioned station; an elec- 

 trometer adapted for absolute measurement, nearly in the form 

 now constructed as an ordinary house electrometer, was used in 

 the lecture-room. Four students of the Natural Philosophy 

 Class, Messrs. Lorimer, Lyon, M'Kerrow, and Wilson, after 

 having persevered in preliminary experiments and arrangements 

 from the month of November, devoted themselves with much 

 ardour and constancy during February, March, and April to the 

 work of observation. During periods of observation, at various 

 times of day, early and late, measurements were completed and 

 recorded every quarter minute or every half minute, — the con- 

 tinual variations of the phenomenon rendering solitary observa- 

 tions almost nugatory. During several hours each day, simulta- 

 neous observation was carried on on this plan at the two stations. 

 A comparison of the results manifested often great discordance, 

 and never complete agreement. It was thus ascertained that 

 electrification of the air, if not of solid particles in the air (which 

 have no claim to exclusive consideration in this respect), between 

 the two stations and round them, at distances from them not 

 very great in comparison with their mutual distance, was largely 

 operative in the observed phenomena. It was generally found 

 that after the indications had been negative for some time 

 at both stations, the transition to positive took place earlier by 

 several minutes at the tower station (upper) than at the lecture- 

 room (lower) . Sometimes during several minutes, preceded and 

 followed by positive indications, there were negative indications 

 at the lower, while there were only positive at the upper. In 

 these cases the circumambient air must have contained negative 

 (or resinous) electricity, if a horizontal stratum of air several 

 hundred feet thick overhead, containing as much positive elec- 

 tricity per cubic foot as there must have been of negative per 

 cubic foot of the air about the College buildings on those occa- 

 sions, would produce electrical manifestations at the earth's 

 surface similar in character and amount to those ordinarily ob- 

 served during fair weather. 



Beccaria has remarked on the rare occurrence of negative 

 atmospheric indications during fair weather, of which he can only 

 record six during a period of fifteen years of very persevering 

 observation by himself and the Prior Ceca. On some, if not all, 

 of those occasions there was a squally and variable wind, changing 

 about rapidly between N.E. and N.W. On several days of un- 

 broken fair weather in April and May of the present year the 

 atmospheric indication was negative during short periods, and 

 on each occasion there was a sudden change of wind, generally 

 from N.E. to N.W., W., or S.W. For instance, on the 3rd of 

 May, after a warm, sunny, and very dry day, with a gentle N.E. 



Phil Mag. S. 4. Vol. 20. No. 134. Nov. 1860. 2 B 



