HERTZIAN WAVE WIRELESS TELEGRAPHY. 59 



can be accumulated only by the prolonged action of impulses tuned to a 

 particular period. 



A mechanical analogue of this difference may be found in consid- 

 ering the different behavior of elastic bodies to mechanical blows. 

 Take, for instance, a piece of elastic steel and fix the bottom end in a 

 vise. The steel strip may be thrown into vibration by deflecting the 

 upper end. It has, however, a very small mass, and therefore any vio- 

 lent blow or blows, even although not repeated, will set it in oscillation. 

 If, however, we add mass to it by fixing at the other end a heavy 

 weight, such as a ball of lead, and at the same time make the spring 

 stiffer, we have an arrangement which is capable of being sent into con- 

 siderable oscillation only by the action of a series of impulses or blows 

 which are timed at a particular rate. 



Keturning then to the electrical problem, we see that in order to pre- 

 serve a kumascope or wave detector from being operated on by any va- 

 grant wave or waves having a period very different to an assigned 

 period, it must be associated with an electrical circuit of the kind above 

 called a stiff circuit. 



We will now consider the manner in which the problem has been 

 practically attacked by Mr. Marconi, Dr. Slaby, Sir Oliver Lodge and 

 others, who have invented forms of receiver and transmitter, which are 

 syntonic or sympathetic to one another. 



Some of the methods which Mr. Marconi has devised for the 

 achievement of syntonic wireless telegraphy were fully described by him 

 in a paper read before the Society of Arts on May 17, 1901.* 



On referring to his paper, it will be seen that in one form his trans- 

 mitter consists of an aerial, near the base of which is inserted the second- 

 ary circuit of an oscillation transformer or transmitting jigger. One 

 end of this secondary circuit is attached to the aerial and the other end 

 is connected to the earth through a variable inductance coil. The pri- 

 mary circuit of this oscillation transformer is connected in series with 

 a condenser, consisting of a battery of Leyden jars, and the two together 

 are connected across to the spark balls which close the secondary circuit 

 of an induction coil, having the usual make and break key in the pri- 

 mary circuit. Mr. Marconi so adjusts the induction of the aerial and 

 the capacity of the condenser, or battery of Leyden jars, that the two 

 circuits, consisting respectively of this battery of Leyden jars and the 

 primary circuit of the transformer, and on the other hand of the capa- 

 city of the aerial and the inductance in series with it, and that of the 

 secondary circuit of the transformer have the same time period. In 

 other words, these two inductive circuits are tuned together. At the 

 receiving end, the aerial is connected in series with a variable induct- 

 ance and with the primary circuit of another oscillation transformer, 



* See Journal of the Society of Arts, Vol. XLIX., p. 505. ' Syntonic 

 Wireless Telegraphy/ by G. Marconi. 



