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 intelligible speech in an ordinary Bell telephone receiver nearly passes belief. The work done in lifting such an instrument from its hook to the ear of the listener, would, if converted into electric energy, be sufficient to maintain an audible sound in a telephone for 240,000 years! Even extremely attenuated waves may therefore produce audible signals in such a receiver.