PROGRESS IN WIRELESS TELEGRAPHY. 



279 



Fi(i. 2.— Liquid detector. 



According to Fessciulcn, this device operates by reason of the fact 

 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 

 L)attery flows throiii>h the shunt circuit, but owing to the high resist- 

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

 electric oscillations decrease this resistance, 

 varying the circuit, and therein' producing 

 audible signals in the telephone. 



According to De 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 nonconduct- 

 ing. Incoming oscillations cause a temporary 

 annulment of the insulating 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 

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

 H. K. Vreeland of this country, and Schloemilch of (lermany, which 

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

 liability of the device. 



Still another autodetector is that successfully employed in the 

 Lodge-Muirhead wireless telegraph systeuL 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 )n. The disk is nor- 

 mally prevented from making direct contact with the mercury by a 

 film of mineral oil. l)ut 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 affect a relay 

 are observable in the former instnunent. Hence, by 



'-'f-'':-Wi ^^^^ "^^' ^^^ ^^^^^ instrument much weaker electric 



J waves are detected than would be the case with the 



filings coherer. Furthermore, the autodetector re- 

 sponds instaneously, so that a higher rate of signaling 

 is ol)tainable by its means, a speed of 40 words a 

 minute having already been obtained by De Forest. 

 Marconi predicts that ultimately he will be able to transmit one 

 hundred words per miinite 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 



Pig. H.—Lodge 

 Muirhead auto 

 detector. 



