178 nature's flbtractes. 



batteries and circuits like that shown in Fig. 

 1, Chapter VI. This was called induction, and 

 is still so called when electrical effects are pro- 

 duced from one wire to another through the 

 ether for short distances. All induction-coils 

 and transformers (see Chapter XXIV) are 

 operated by effects produced through the ether 

 from the primary to the secondary coil but 

 through very short distances. 



In 1880 Professor Trowbridge transmitted 

 an electrical current through the earth for one 

 mile so as to produce signals in a teleph< i<-. 

 In 1881-2 Professor Dolbear used for a short 

 distance (fifty feet) substantially the same ar- 

 rangement as Marconi now uses, except that 

 the former used a telephone as a receiver. 1 1 - 

 used an induction-coil having one end of the 

 secondary wire connected with the earth, while 

 the other was attached to a wire running up 

 into the air. At the receiving-end a wire 

 starting from the earth extended into the air, 

 passing through a telephone, which acted as a 

 receiver. In 1886 he used a kite to elevate the 

 wire, through which electrical discharges of 

 high voltage were made into the air to pro- 

 duce ether-waves the receiver being 2000 feet 

 away. Dolbear's experiments were public 

 fourteen years ago, but at that time there was 

 no interest in such matters, so that his work 

 received little or no attention. In 1887 Dr. 

 Hertz of Germany made some experiments in 



