640 



SCIENCE. 



[N. S. Vol. XX. No. 515. 



Table II. Vertical Eaeth-aie Electric 



Currents. 

 [Plus sign means upward currents ; whereas minus 

 sign implies downward currents.] 



of electricity passing per second of time 

 from the earth to the air is 120 X 10* 

 amperes; dividing the latter quantity by 

 the total area of the zone, the upward cur- 

 rent is found to average for the zone 40 N. 

 to 50 N., 0.038 ampere per square kilo- 

 meter. The quantities i in the last column 

 give a maximum downward current in the 

 zones 20 N. to 30 N. and 20 S. to 30 S., 

 and upward currents near the equatorial 

 belts, and again beyond parallels 30°. 



The general conclusion to be drawn ap- 

 pears to be: 



All of the modern magnetic charts — i. e., 

 since those of Sahine for 1840-5 — unite 

 in indicating the probable existence of ver- 

 tical earth-air electric currents of the av- 

 erage intensity over the region 45° N. to 

 45° S. of one thirtieth of an ampere per 

 square kilometer of surface. These cur- 

 rents of positive electricity proceed upward 

 (from the earth into the air) near the 

 equatorial regions where there are ascend- 

 ing air currents, and downward near the 

 parallels 25° to 30° , i. e., in the regions of 

 descending air currents. Near the paral- 



lels 40° the electric currents are again up- 

 ward, thus corresponding once more with 

 the general atmospheric circulation. Be- 

 yond the parallels 45° the results appear 

 too wncertain to warrant drawing a defi- 

 nite conclusion. 



If it be true that the vertical electric 

 currents are to be associated with air cur- 

 rents, and are hence convection currents, 

 the importance of choosing circuits for 

 testing the validity of the potential hypoth- 

 esis in localities of steady air currents is 

 made manifest. It is thus clear that 

 meteorological conditions may play an im- 

 portant part — as already pointed out in 

 my 1897 paper— in investigations as to the 

 existence of vertical electric currents from 

 magnetic surveys over limited areas. 



In order to make some tests as to the 

 manner of distribution of the upward and 

 downward electric currents, the currents 

 over quadrilaterals bounded by two paral- 

 lels 10° apart and two meridians, likewise 

 10° apart, have been derived for the entire 

 region from 60° N. to 60° S., for the three 

 epochs 1842, 1880 and 1885. As a general 

 result, it did not appear as though the di- 

 rections of the electric currents— whether 

 up or down — were to be associated with the 

 distribution of land and water. There was, 

 however, a decided indication, for each 

 epoch, that over the areas of low pressure, 

 where the air-currents are upward, there 

 the electric currents were likewise, in gen- 

 eral, upward, and that over the areas of 

 high pressure where there are descending 

 air-currents, there the electric currents 

 were likewise descending. 



Thus, as the average result, from the 

 three epochs we have: 



Region. Quantity of Electricity 



60° N. to f for areas of low pressure : + 829 X 10* amperes 

 60° S. i " " " high " : — 638X10* 

 (+ means upward electric currents; — , downward elec- 

 tric currents.) 



The average effect of electric currents 

 for the region 45° N. to 45° S. is on the 



