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[Presented to the Congress of Electricians, Paris, September 17, 1881, and here 

 translated from their Proceedings] 



[Johns Hopkins University Circulars, No. 19, pp. 4, 5, 1882] 



Among the subjects to be discussed by this Congress is that of atmos- 

 pheric electricity, and I should like, at this point, to urge the import- 

 ance of a series of general and accurate experiments performed simul- 

 taneously on a portion of the earth's surface as extended as possible. 

 Here and there on the globe, it is true, an observer has occasionally 

 performed a series of experiments, extending even over several years: 

 but the different observers have not worked in accordance with any pre- 

 concerted plan, it has not been possible to compare their instruments, 

 and even where absolute measurements have been obtained, the exact 

 meaning of the quantity measured has not been perceived. Let us 

 take, for instance, Sir William Thomson's water dropping apparatus, 

 which is used at the Kew Observatory. This apparatus is composed 

 of one tube rising a few feet above the building and of another tube 

 near the ground, so that it is in the angle made by the house and the 

 ground. This apparatus indicates a daily variation in the electricity 

 of the atmosphere, but the result is evidently influenced by the condi- 

 tions of the experiment. Another observer who should fit up an appar- 

 atus in another country might obtain entirely different conditions, so 

 that it would be impossible to compare the results. Hence the neces- 

 sity of having a system. 



The principal aim of scientific investigation is to be able to under- 

 stand more completely the laws of nature, and we generally succeed in 

 doing this by bringing together observation and theory. In science 

 proper, observations and experiments are valuable only in so far as they 

 rest on a theory either in the present or in the 'future. We can as yet 

 present only a plausible theory of atmospheric electricity, but the real 

 way of arriving at the truth in this case is to let ourselves be guided in 

 our future experiments by those which have hitherto been made on 

 this subject. 



