140) J. Trowbridge—The Earth as a Conductor of Electricity. 
tance from the grounds of the battery increases, in order to per- 
mit of one end of the wire touching a point of higher potential 
than the other. 
The theoretical possibility of telegraphing across the Aflan- 
tic without a cable is evident from this survey which I have 
undertaken. The practical arales ge is another question. 
At no point in our survey did we find an absence of earth 
currents. The peculiar crackling noises heard in telephones 
are due to earth currents and not to fluctuations in the batteries 
employed on acevo circuits; for they were Ye acmpanletig of 
the circuits employed by us in ‘which the earth was used as a 
part of the circuit, and were absent when a baibery ernie was 
closed without the intervention of the earth. e tick pro- 
to polarization between the copper wire and the moisture of the 
ground, for it was many hundred times stronger than the polar- 
ization effect produced by dipping the copper terminals of the 
telephone wire in acidulated water. This crackling noise pro- 
duced by the earth si ony in a telephone is a curious phe- 
_ nomenon, and shows that the earth currents have a satin’ 
earth currents, is much to be here. In some cases the igo 
satory effect of these earth currents was very marked. At no 
point which we explored, were evidences of earth currents 
absent. They cod to be more pronounced along water 
courses. 
In a discussion of the earth as a conductor, Steinheil says: 
“We cannot conjure up gnomes at will, to convey our 
thoughts through the earth. Nature has prevented this. The 
the earth without ys pots con uctors. ut it is not pro 
ble that we shall ever attain this end.” 
Theoretically, however, it is iti to-day to ssenrapy 
across the Atlantic Ocean without a cable. Powerful dynam 
electric machines could be placed at some point in Nova Sco. 
tia, having one end of their circuit grounded near them and 
the other end grounded in Florida, the conducting wire con- 
* Die Anwendung des Elektromagnetismus, p. 172, 2d ed., 1873. 
