NOVEMBEK 11, 1904.] 



SCIENCE. 



639 



existence of vertical electric currents pass- 

 ing through the earth's crust, as revealed 

 by Schmidt 's analj^sis. He found that there 

 was ou the average for the entire earth, 

 for every square kilometer of surface, a 

 current of one sixth of ampere, passing 

 perpendicularly through the surface, either 

 from the air into the earth or vice versa. 

 However, as certain investigators found it 

 difficult to harmonize a current of this 

 strength with the known phenomena of 

 atmospheric electricity, and since similar 

 investigations conducted over well-sur- 

 veyed, though restricted, areas by several 

 eminent magnetists did not reveal these 

 currents, Schmidt was led to doubt his re- 

 sult and ascribe it to systematic map errors. 

 The existence of these currents is re- 

 vealed by the non-vanishing of the line 

 integral of the magnetic force taken around 

 a closed curve on the earth 's surface. Such 

 line integrals serve as a test of the hypoth- 

 esis of a potential, as was first shown and 

 approximately applied by Gauss. Let us 

 choose, as our circuit, a parallel of latitude, 

 and let us call, as is customary, the com- 

 ponent of the horizontal magnetic force 

 resolved in a west-east direction, the Y 

 component, then, if d\ is the element of the 

 parallel, 



rMA=o, 



Jo 



if the earth's entire magnetic force is due 

 to a potential. If, on the other hand, 

 electric currents of the kind mentioned 

 exist, then, if I represents the total amount 

 ■of electricity passing per second of time 

 through the zone from the north geograph- 

 ical pole down to the parallel around which 

 the circuit is made, expressed in electro- 

 magnetic units, we have: 



47r Jo 



FrfX. 



In a paper published in 1897 I com- 

 puted the values of I for every fifth par- 



allel from 60° N. to 60° S. as based on 

 Neumayer's magnetic charts for 1885, and 

 also gave a graphical representation along 

 a meridian of the average distribution of 

 the currents found. The resulting system 

 was such a methodical one as to strongly 

 suggest that there might be some truth, 

 after all, in the existence of vertical earth- 

 air electric currents. 



With the aid of the facilities of the De- 

 partment of Terrestrial Magnetism of the 

 Carnegie Institution, I recently have had 

 my calculations for 1885 repeated for two 

 other epochs, viz., first, as based upon Sa- 

 bine's magnetic charts for 1840-5, which 

 depended upon magnetic data distributed 

 over about seven decades, with the date 

 1840-5 about in the middle of the series 

 and secondly, as based upon Creak's charts 

 for 1880 issued just after the magnetic re- 

 sults of the Challenger expedition were 

 available to him. 



A further check upon the computations 

 was obtained by a consideration of the 

 magnetic declination charts alone, viz., for 

 four epochs— Sabine (1840-45), British 

 Admiralty (1858), Creak (1880) and Neu- 

 mayer ( 1885 ) . The calculations were based 

 on the following principle: the downward 

 electric currents will deflect the north end 

 of a magnetic needle to the west, whereas 

 the upward currents will deflect the north 

 end to the east. The results obtained thus, 

 agreed well with that obtained from the 

 Y components. 



The mean results as derived from all the 

 computations are given in the table on the 

 following page. 



For example, through the region of the 

 earth between the parallels 50° north and 

 the equator, the resultant quantity of elec- 

 tricity passing every second of time from 

 the air into the earth amounts to 419 X 

 10* amperes. In the zone between the two 

 parallels 50° N. and 40° N., the resultant 

 currents are upward and the total amount 



