HISTORY OF ELECTRICAL RESOXA^'CE 



429 



commercial practicability it would be necessary to provide means for 

 receiving one wave-length to the exclusion of others — to provide selectivity. 

 Crookes in his prophetic Fortnightly Review article of 1892 had clearly 

 envisaged this.-^ As a solution of this problem Lodge in 1897 applied for a 

 British patent on "Improvements in Syntonized Telegraphy without Line 

 Wires,"-^ the stated object of his invention being "to enable an operator by 

 means of what is known as Hertzian wave telegraphy to transmit messages 



Fig. 5 — The tuned inductively coupled two-circuit radio transmitter adopted by 



Marconi in 1900. 



across space to any selected one or more of a number of different individuals 

 in various localities each of whom is provided with a suitably arranged 

 receiver." His radiator, modeled after Hertz, was a pair of "capacity 

 areas", or triangular shaped metal plates (one of them preferably grounded), 

 separated by a spark gap and having interposed an inductance coil of a few 

 turns, for the purpose of tuning. This coil was not continuously adjustable 

 but was to be replaced by others for changes of wave-length. The receiving 



