OBSERVATIONS Of ATMOSPHEEIC ELECTRICITY. 443 



Observations of Atmospheric Electricity at the Kew Observatory 

 during 1880. By (x. M. Whipple, B.Sc, F.R.A.S., F.M.S.^ 

 Superintendent. 



[A communication ordered by the General Committee to be printed in cxtensa 



among tlie Ecports.] 



[Plate VII.] 



The results of the observations of Atmospheric Electricity made at the 

 Kew Observatory have been published at various times, but principally 

 in a long paper of eiglity-seven pages in the Report of the British 

 Association for the year 1849, by Mr. W. R. Birt, F.R.A.S., and in a paper 

 by Professor Everett, F.R.S., in the ' Philosophical Transactions ' for 

 1868. 



The first paper treated of the eye-observations made by the aid of the 

 beautiful apparatus designed by the late Sir Francis Ronalds, whilst the 

 latter was based on the reduction of the photographic continuous records 

 derived from Sir William Thomson's well-known divided ring Electro- 

 meter, in connection with a water-dropping collector. 



Since the beginning of 1873 a quadrant Electrometer has been in 

 almost constant work. By the kindness of Mr. De La Rue, who allowed 

 the use of his large chloride of silver battery for the purpose, the value 

 in absolute measure of the deflections of this instrument has been deter- 

 mined, and therefore we are now able to give the potential of the Atmo- 

 sjjheric Electricity at Kew from time to time in volts instead of in arbitrary 

 values, as has been done in preceding discussions. 



Owing to the incessant and frequent changes in the atmospheric 

 tension, the tabulation of the photographic traces with any degree of 

 certainty entails a considerable amount of labour, and although Professor 

 Everett devised a most ingenious method of obtaining the hourly mean 

 values from the curves, yet we found it impossible in the ordinary 

 work of the Observatory to devote the time to the instrument that it 

 necessitated, and hence our seven years' indications have up till recently 

 remained unavailable for discussion. 



Lately I succeeded in devising a modification of Professor Everett's 

 method, and constructed a glass scale, by means of which the tabulation 

 of the curves can be efiected with the greatest facility and expedition. 

 Accordingly we have now commenced the tabulation and discussion of 

 the accumulated records, and, by the kind permission of the Meteorogical 

 Council, I am able to lay a few of the facts derived from the curves for 

 1880 before the members of the British Association. 



Having determined the values of the atmospheric tension for every 

 hour during the year, when measurement of the trace was possible, the 

 diurnal, monthly, and annual variations were computed. 



For brevity I only give here the values of the mean monthly, diurnal, 

 and annual ranges, which are as follows. See Tables I. and II. 



Having plotted these, the curves wei'e contrasted with those given by 

 Mr. Birt and by Professor Everett, with the view of finding Avhat, if any 

 difference, in the phenomena observed may be attributed to instrumental 

 causes. 



As Mr. Birt in his discussion treats separately the positive and nega- 

 tive tensions, we have also omitted the negative readings, which are com- 

 paratively few in number, and compared the results with the similar values 



