136 
It is, after all, the genius of Maxwell and of a few other great theo- 
retical physicists, whose names are on every one’s lips, which 
endows the simple induction experiments of Hertz and others with 
such stupendous importance. Here is the quotation: 
“¢«Tn extending the researches relative to this part of the investi- 
gations, a remarkable result was obtained in regard to the distance 
at which induction effects are produced by a very small quantity of 
electricity ; a single spark from the prime conductor of a machine 
of about an inch long, thrown on to the end of a circuit of wire in 
an upper room, produced an induction sufficiently powerful to mag- 
netize needles in a parallel circuit of iron placed in the cellar be- 
neath at a perpendicular distance of thirty feet, with two floors and 
ceilings each fourteen inches thick intervening. The author is dis- 
posed to adopt the hypothesis of an electrical p/enum’ [in other 
words, of an ether], ‘and from the foregoing experiment it would 
appear that a single spark is sufficient to disturb perceptibly the 
electricity of space throughout at least a cube of 400,000 feet of 
capacity; and when it is considered that the magnetism of the 
needle is the result of the difference of two actions, it may be fur- 
ther inferred that the diffusion of motion in this case is almost com- 
parable with that of a spark from flint and steel in the case of 
light.’ Comparable it is indeed,’’ says Lodge, ‘‘ for we now know 
it to be the self-same process.”’ 
A few months later Henry ‘‘ succeeded in magnetizing needles by 
the secondary current in a wire more than three hundred feet distant 
from the wire through which the primary current was passing, ex- 
cited by a single spark from an electrical machine.’’* The primary 
wire used for this purpose was the telegraph line which he had 
stretched seven years before across the campus of the college 
grounds in front of Nassau Hall; the secondary or induction wire 
being suspended in a parallel direction across the grounds in the 
rear of Nassau Hall, its ends terminating in buried metallic plates. 
The building itself intervened between the wires. 
Moreover, Henry studied induced currents produced by atmos- 
pheric electricity. By avery simple arrangement he was enabled 
to magnetize needles strongly in his study, whenever a lightning 
flash took place within a radius of twenty miles and when the thun- 
der was scarcely audible. ‘‘ The inductions from atmospheric dis- 
* Proceedings Amer. Philos. Soc., Vol. ii, p. 229, Oct. 21, 1842. Vol. iv, p. 260, June 19, 1846, 
