PROGRESS IN WIRELESS TELEGRAPHY. 



279 



Fig. 2.— Liquid detector. 



According to Fess(Mi(l(Mi, this device operates by reason of the faet 

 that practically all the resistance of the circuit is localized and con- 

 centrated within a short distance of the point where the cylindrical 

 platinum wire projects into the liquid. The current from the small 

 battery flows throui>-h the shunt circuit, but owin<^ to the hiijh i-esist- 

 ance of the circuit this current is nornudly weak. The incoming- 

 electric oscillations dc^crease this resistance, 

 varying the circuit, and thereby producing 

 audible signals in the telephone. 



According to I)e Forest, the operation of this 

 detector is due to the setting up of a counter 

 electromotive force of polarization in the cell, 

 which makes the cell apparently noncon(bu-t- 

 ing. Incoming oscillations cause a temporary 

 annulment of the msulating film of oxygen gas surrounding the posi- 

 tive electrode, varying the current in the local circuit, with the desired 

 result of producing signals readable on the telephone. There are 

 noAv two other claimants for the inventorship of this detector, namely, 

 H. K. Vreeland of this country, and Schloemilch of Gernuiny, which 

 fact may be considered a fair indication of the practicability and re- 

 liability of the device. 



Still another antodetector is that successfully employed in the 

 Lodge-Muirhead wireless telegraph system. It is shown in figure 3 

 and is known as the oil-film detector. It consists, essentially, of a 

 rotating steel disk D', operated by clockwork. The periphery of 

 this disk enters a vessel r containing mercury m. The disk is nor- 

 mally prevented from making direct contact with the mercury by a 

 film of mineral oil, but electric oscillations in the circuit cause the 

 mercury and disk to cohere with the usual result. 

 The detector circuit is completed by wires w w\ 



By reason of the sensitiveness of the telephone re- 

 ceiver, changes of current that would not att'ect a relay 

 are observable in the former instrument. Hence, by 



?- ,-^ the use of this instrument much weaker electric 



waves arc detected than would be the case with the 

 filings coherer. Furthermore, the antodetector re- 

 sponds instaneously, so that a higher rate of signaling 

 is obtainable by its means, a speed of 10 words a 

 minute having already been obtained by De Forest. 

 Marconi predicts that ultimately he Avill be able to transmit one 

 hundred words per miimte by means of his detector and suitable auto- 

 matic transmitting and receiving apparatus. 



Important improvements have also been made in the matter of 

 syntonic, or tuned, windless telegraphy, by means of which it is 

 hoped to eventually transmit two or more different messages at the 



Fig. 3.— Lodge- 

 Muirhead auto- 

 detector. 



