OBSER 7 A Tl ONS OF A TMOSPHERIC ELECTRICITY. 33.> 



These tests seemed to show that natural currents in land lines were the con- 

 tinuations of the su.bmarine currents which were arrested by the compara- 

 tive non-conductivity of the land, for on Mr. Yarley's endeavouring to find 

 the neutral, or equi-potential, line for the currents of the east coast of Eng- 

 land, he found it to coincide approximately with the shore line. 



During auroras these currents become extremely strong, sometimes as 

 great as can be produced by the employment of a battery of 2000 of Daniell's 

 cells, and occasionally even exceeding this. Of such currents the most ex- 

 tensive set of simultaneous observations that have been made was during 

 the remarkable aurora of February 4, 1872 ; but as on that occasion these 

 observations were not the result of any general system of measurement, but 

 owed their origin to the fact that the currents became so strong as to inter- 

 fere with the working of all the telegraph lines throughout the world, it 

 cannot be expected that any large amount of information can be derived 

 from the mass of records made on that day. One point however can be 

 learnt from these observations, and that is this — first, the general direction of 

 the positive currents was from East to West, that is, with the sun ; secondly, 

 along lines running North and South the currents were comparatively weak. 



There seems to be no doubt now that the earthquakes are preceded, or 

 accompanied, by unusual strong natural currents in telegraph lines. As far 

 as we are aware, attention was first drawn to this by one of the writers of 

 this paper in a communication made to the Asiatic Society of Bengal, in June, 

 1871, in connection with the Indian earthquake of February 16, of that year. 

 The Indian earthquake again of December 15, 1872, jireceded by such 

 strong earth currents during the evening of December 14th in the land lines 

 from Yalentia to London, that in order to send messages it was necessary to 

 loop the lines, by means of which the current in the one line was made to 

 neutralize that in the other. The Egyptian earthquake of January 12, 1873, 

 was preceded for some days by equally strong natural currents. This earth- 

 quake was also accompanied by an eruption of the volcano Shaptar Jokull 

 in Iceland, which lasted from January 9 to January 12, and it is interesting 

 to notice, as Mr. Graves, of the Atlantic Cable Co., has pointed out, that a 

 direct line drawn from Cairo to Iceland crosses the telegraph wires from 

 Valentia to London. Again, the Italian earthquake of March 17, 1875, was 

 accompanied by great disturbances on the land lines of Italy. 



From what has preceded, it maybe concluded with a fair amount of cer- 

 tainty, that (1) atmosphere electricity, (2) auroras, (3) earthquakes, (4) 

 magnetic distances, (5) natural currents in telegraph lines, (6) sun spots, 

 and (7) wind storms, are all linked together, and we feel that if this is 

 shown, nothing more is needed to induce thinking people to interest them- 

 selves in the subject of this paper. 



As regards the method of measuring the atmospheric potential, we have 

 not much to add. Sir Wm. Thomson's quadrant electrometer, combined 

 with his water-dropping collector, forms a very delicate measuring appara- 

 tus for observatories, and can easily be made self-recording; his probable 



