oroscope and the photographic camera have proved an
invaluable aid to the surgeon, who can now look directly through the
human body and examine its internal organs, and so be able to locate
such foreign bodies as bullets and needles in its various parts, or make
correct diagnoses of fractures or dislocations of the bones, or even
examine the action of such organs as the liver and heart.

About 1886, Hertz discovered that if a small Leyden jar is discharged
through a short and simple circuit, provided with a spark-gap of
suitable length, a series of electro-magnetic waves are set up, which,
moving through space in all directions, are capable of exciting in a
similar circuit effects that can be readily recognized, although the two
circuits are at fairly considerable distances apart. Here we have a
simple basic experiment in wireless telegraphy, which, briefly
considered, consists of means whereby oscillations or waves, set up in
free space by means of disruptive discharges, are caused to traverse
space and produce various effects in suitably constructed receptive
devices that are operated by the waves as they impinge on them.

At first a doubt was expressed by eminent scientific men as to the
practicability of successfully transmitting wireless messages through
long distances, since these waves, travelling in all directions, would
soon become too attenuated to produce intelligible signals; but when it
was shown, from theoretical considerations, that these waves when
traversing great distances are practically confined to the space between
the earth's surface and the upper rarified strata of the atmosphere, the
possibility of long-distance wireless telegraphic transmission was
recognized. To increase the distance, it was only necessary either to
increase the energy of the waves at the transmitting station, or to
increase the delicacy of the receiving instruments, or both.

It has been but a short time since both the scientific and the financial
worlds were astounded by the actual transmission of intelligible
wireless signals across the Atlantic, and the name of Marconi will go
down to posterity as the one who first accomplished this great feat.

The principal limit to the distance of transmission lies in the delicacy
of the receiving instruments. The most sensitive are those in which a
telephone receiver forms a part of the receiving apparatus. The almost
incredibly small amount of electric energy required to produce
int