270 WIRELESS TELEGRAPHY. 



The tuned receiving apparatus is shown in fig. 8. In this figure, A 

 is again the vertical wire with the turns of wire v\ to which is attached 

 the primary wire p of the induction coil T; d is the secondar\' of the 

 same induction coil; ck are "choke'' coils; A- is the coherer, c is a con- 

 denser, and R is the relay. The induction coil T acts virtuallj^ as a 

 step-up transformer, materiall}^ enhancing the electromotive forces of 

 the received oscillations, and thus increasing the signaling distance. 



Marconi has found it important that the oscillation period of the 

 coherer circuit, shown in the figure in solid lines, shall be the same as, 

 or an octave of, the oscillation period of the vertical wire circuit, 

 shown by the dotted lines. This can be done by making the secondary 

 coil ^j), of the coil T^ equal the length of the vertical wire A. The 

 transmitter circuit is then adjusted so that its oscillation period cor- 

 responds with that of the receiving circuit. This is brought al)out by 

 varying the capacity of the condenser in fig. 7. The method of obtain- 

 ing this "balance," as practiced by Marconi, is to begin with very 

 little capacity in the condenser, and adding to it until the best results 

 are obtained at the receiving station. If, when the best results are 

 obtained, still further capacity is given to the condenser in the trans- 

 mitting circuit, the signals fade away, showing that then the two circuits 

 are out of harmony. 



Marconi also found that b}^ means of tuned apparatus a much greater 

 distance may be reached, with a given soui'ce of electrical energy and 

 height of wires. For example, a transmitter which would ati'ect a 

 tuned receiver 30 miles away would not afi'ect a nontuned receiver 

 160 feet distant. This, it may be assumed, is because in the case of 

 the tuned receiver the faintest oscillations, or electromotive forces, set 

 up in the receiving circuit by the incoming waves are in unison with 

 those waves, and successive incoming waves amplify the oscillations in 

 the receiver circuit until they affect the coherer; whereas the oscilla- 

 tions which the same waves tend to set up in the nontuned receiver 

 circuit are, so to speak, out of step with the natural rate of oscillation 

 of the nontuned circuit, and thus as frequently oppose as assist the 

 natural oscillations of the circuit. 



In connection with the experiments carried on by Marconi, it is 

 reported that two difi'erent messages have been received at one time 

 on a vertical wire, two sets of receiving apparatus, each attuned to a 

 different rate of oscillation, being connected with the same wire. To 

 those who have had experience with (Iray's harmonic system of wire 

 telegraphy," in which three and four instruments, attuned to transmit 

 and to receive different rates of electrical current pulsations, have 

 been successfully and separately operated on one wire, this Avill not 

 appear astonishing, since it is quite conceivable, if it be granted that 

 wireless transmitting and receiving apparatus can ))e successfully 

 attuned, that two or more receiving instruments might be connected 



« Described in Mavcr's American Telegrapliy, fifth edition. 



