Intelligence and Miscellaneous Articles, 315 



surface, the action upon an element situated at the summit and 

 directed along the axis will be nil. The presence of the arbitrary- 

 constant in equation (4) permits the surface to be made to pass 

 through any point whatever of space ; and consequently there exist 

 in each point an infinity of directions in which an element els' may 

 be placed so as to annul its action upon the given element ds. 

 Those directions are all in the tangent plane to the surface found. 

 It is readily seen that the action is a maximum when the element 

 is normal to the surface, and that, for an element of given length 

 and intensity, it is proportional to the cosine of the angle made with 

 the normal. If the element ds, placed along the axis of the surface, 

 is directed outward, every element starting from a point of the 

 same surface and like it directed outward will be repellent, and 

 every element directed inward will exert an attractive action. — 

 Coniptes Bendus cle VAcademie des Sciences, vol. lxxix. pp. 141-143. 



ON EARTH-CURRENTS. BY L. SCHWENDLER, ESQ.* 



Mr. Schwendler said that the phenomenon of earth-currents 

 seemed to be intimately connected with the earth-magnetism and 

 its variations. 



He would, however, point out from the beginning that though 

 the two phenomena, "earth-magnetism" and "earth-currents," 

 were undoubtedly connected with each other, it was by no means 

 established as yet that they were cause and effect, or, what certainly 

 seems to be far more probable in the present state of knowledge on 

 the subject, parallel effects of one and the same general but en- 

 tirely unknown cause. 



The three elements of the earth-magnetism, intensity, inclination, 

 and declination, had been quantitatively and most accurately deter- 

 mined in almost all civilized parts of the world (Calcutta excepted) 

 by the introduction of G-auss and Weber's well-known system of 

 magnetic measurements ; and though the results obtained had been 

 very general and satisfactory, establishing the most interesting 

 facts of diurnal and secular periods of variation in the three mag- 

 netic elements, and had also been of direct practical benefit to na- 

 vigation, still the physical nature of the phenomena had not been 

 unveiled by these observations. To solve the problem, it would 

 seem that quantitative measurements of other phenomena, directly 

 or indirectly connected with it, were required ; and it was most for- 

 tunate that at least one such phenomenon not only existed but was 

 even susceptible of accurate measurement ; he meant the " earth- 

 currents." 



The chances of giving a true physical explanation of any pheno- 

 menon, he observed, increased in geometrical progression with the 

 number of phenomena directly or indirectly connected with the one 



* Communicated by the Author, from the proceeding's of the Asiatic 

 Society of Bengal for June, 1874. 



