Intelligence and Miscellaneous Articles. 317 



starts, as was the case during magnetic storms, it would be almost 

 hopeless to attempt a general system of measurement. This was, 

 however, fortunately not the case, since these earth-currents, which, 

 during magnetic storms became so violent, seemed to exist perma- 

 nently, only of very feeble strength ; and it was on this subject that 

 he would give some observed facts." 



The general outline of the rest of Mr. Schwendler's commmuni- 

 cation will be best given in extracts from his paper, which will be 

 printed in full in Part II. of the Journal. 

 Mr. Schwendler says : — ■ 



" The currents observed at all hours of the day and all seasons of 

 the year, in every line throughout India, may be obviously due 

 to many different causes acting separately or conjointly. These 

 currents I have designated ' natural currents,' to indicate the fact 

 of their being in the lines without any direct, or at least intentional, 

 human agency. The causes which may produce natural currents 

 in telegraph-lines are : — 



" 1. Gralvanic action between the earth-plates. 

 "2. Polarization of the earth-plates by the signalling-currents. 

 " 3. Polarization of badly insulated points in the line. 

 " 4. Atmospheric electricity. 

 "5. Thermo-electricity. 

 "6. Inductive capacity. 

 "7. Voltaic induction. 

 "8. Earth-currents. 



" The latter must be regarded as produced by an actual difference 

 of potentials between the two points of our planet with which the 

 ends of a telegraph-line are in contact. 



" Surely if these ' earth-currents ' do permanently exist, and, fur- 

 ther, if they are strong enough to overpower the others, which are 

 evidently of a much more accidental and less permanent nature, 

 then a large number of quantitative observations, judiciously re- 

 duced and conveniently compiled, should at least show the tendency 

 of the general law that governs them in strength and direction, 

 leading perhaps finally to the true explanation of the earth's mag- 

 netism and the causes of its variations. 



" Such were in short my reasonings when, in 1868, 1 was intrusted 

 by Colonel Robinson, the Director-Greneral of Telegraphs, with the 

 introduction of a system of testing the lines in India ; and although 

 the practical objects of that system had nothing whatsoever to do 

 with the solution of the problem, yet the fact that in each test measure- 

 ments had to be made with positive and negative currents (for the 

 very purpose of eliminating the influence of the natural currents) 

 secured all the data necessary for the quantitative determination of 

 the electromotive force in the line, to which the natural current 

 must be considered proportional, involving only a slight additional 

 calculation without any extra observations. To this end the neces- 

 sary provisions were made and instructions issued; and in this 

 manner more than 10,000 electromotive forces, producing the 

 natural currents in the lines of India, have been calculated from the 



