262 WIRELESS TELEGEAPHY. 



like the torches in the Polybiiis system, corresponded to certain let- 

 ters of the alphabet, and by varying the position of the arms as 

 required experts were able to transmit messages from one station to 

 the other at the rate of two or three words per minute. The towers 

 on the top of which the semaphores were erected were often 50 to 60 

 feet high, and were placed on eminences about 6 or 8 miles apart. In 

 Russia alone there was a string of these towers from the Prussian 

 frontier to St. Petersl)urg, a distance of 1,200 miles or more. Then, 

 after the electric wire telegraph, came the electric wireless telegraph, 

 and perhaps even a cursory review of this subject will show that it is 

 not of as recent origin as it is popularly thought to be. For instance, 

 it is known that over one hundred and fifty years ago electric signals 

 were sent Avithout wires across lakes and rivers. Dr. Watson, bishop 

 of Landorff, then sent electric shocks across the Thames, and, subse- 

 quentl}^ through the New River at Newington. Similar experiments 

 were made by Franklin in 1748 across the Schuylkill at Philadelphia, 

 and by Du Luc, a yeav later, across the lake of Geneva. In these 

 instances, however, the water or earth was the conductor of the elec- 

 tric impulses. 



It is fairly well known also that during the past fifteen or eighteen 

 years there have l)een in limited use a numl)er of wireless telegraph 

 systems which have sometimes been termed induction telegraph sys- 

 tems, and in which electromagnetic impulses, or waves, are employed. 

 Such systems are ])ased upon the phenomena of mutual induction 

 between wires, discovered b}" Faraday and Henr3\ Henry's experi- 

 ments, made half a centur}^ ago, were chiefly with flat coils of wire, 

 one opposite the other. When the circuit of one of such coils, con- 

 taining a battery, was opened and closed, it was found that an electric 

 current was set up in the other coil. This action also takes place 

 between two straight, parallel wires, and when these parallel wires are 

 sufficient]}^ h)ng, and the electromotive force in the transmittnig wire 

 is powerful enough, signals may be received in a telephone or other 

 sensitive receiver, even when the wires are separated a distance of 

 several miles. 



In 1892 Sir William II. Preece succeeded in transmitting Morse 

 signals by this method to a distance of more than 3 miles, between 

 Penarth, on the mainland, and the island of Flat Holm, in the British 

 Channel, using a telephone as the receiver. More recently the same 

 experimenter has met with success in establishing a wireless telephone 

 circuit by means of which speech is transmitted between the Skerries 

 light-ship and the mainland of Anglesey — a distance of nearly 3 miles — 

 the parallel wiie on the Skerries Islands being 750 yards in length and 

 that on the mainland 3.5 miles in length, the ends of each wire terminat- 

 ing in the sea. On these systems both magnetic induction and electric 

 conduction through the earth and water are utilized. 



