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WIRELESS TELEGRAPHY. 
the way of experimentally verifying Clerk Maxwell's theory, and the 
theory remained for many years little more than a pious belief among 
the school of mathematical physicists founded by Maxwell, and was 
doubted by a great many scientists—especially on the continent. 
However, it remained for a scientist on the continent,—Hertz in Ger¬ 
many^—to set all doubts at rest and to triumphantly vindicate Max¬ 
well's theory; for by a brilliant series of experiments he demonstrated in 
a conclusive manner the existence of those electro-magnetic radiations ; 
and not only that but proved that the waves are capable of being re¬ 
flected, refracted and polarised,—they showed, in fact, all the phenomena 
of Light waves. 
The fact which enabled Hertz to detect the radiations is this:— 
If a series of electro-magnetic waves, set in motion by electric oscil¬ 
lations, find in their path a conductor or system of conductors, they 
tend to set up an electric oscillation in the conductor, which will be the 
more marked if the conductor by reason of its capacity, inductance, 
and resistance, tends to oscillate electricity with exactly the same fre¬ 
quency as the initial oscillator, in which case the action is called reson¬ 
ance. This action can be illustrated by a very well-known^phe¬ 
nomenon connected with sound waves. If anyone strikes a tuning 
fork in the vicinity of a number of different tuning forks, those forks 
whose note is the same or a harmonic of the forks struck, will be set 
vibrating—and again let any one sing a sustained note close to a 
piano, he will notice that the piano wire tuned to the same note will 
vibrate as also will its harmonics in a lesser degree. 
Similarly with electric vibrations. I do not ask you to be¬ 
lieve this statement without showing you something in the nature of 
an experiment confirming it. I must ask you to accept thisTact : 
When you see a stream of sparks across the spheres of the trans¬ 
mitting apparatus (Plate II.) you must imagine that each spark con¬ 
sists of a number of oscillations taking place perhaps at the rate of 
about 250,000,000 per second. Each oscillation starts an electro¬ 
magnetic wave at right angles to the line of oscillation; the wave 
moves outwards with the velocity of light, 186,400 miles per second. 
The wave length is accordingly about 4 feet long. I place here in 
the path of the waves a conducting system (receiver) similar to that of 
the transmitter. The receiver consists of two pieces of pointed carbon 
rod supported by two brass rods. At the outer end of the carbon 
rods two copper “ wings " are ".fixed, the function of which are to tune 
the receiver, more or less, to the transmitter. A minute gap separates 
the carbon rods. If the key controlling the transmitter be depressed 
(causing sparks to pass across the transmitter spheres) a series of 
sparks can be observed to pass across the small gap between the carbon 
points, although no material connection of any kind exists with the 
transmitter. (Experiment shewn :—The fact of the sparks passing 
confirmed by one of the audience). 
These sparks are visible only by careful and close observation, 
but in order to make the fact obvious to everyone in the room, I adopt 
an expedient to show unraistakeably to everyone that the sparks really 
