276 PROGRESS IN WIRELESS TELEGRAPHY. 



The art, however, received its most powerful impetus when Mar- 

 coni, in 1898, using vertical Avires 80 to 100 feet high at each station, 

 a 10-inch spark induction coil, and an improved Branly-I^odge co- 

 herer, succeeded in transmitting Avireless signals a distance of about 

 40 miles, which distance within another twelve months, by using still 

 higher vertical wires and more improved apparatus, he increased to 

 380 miles over water. 



The writer on other occasions has remarked tllat had the progress 

 of Avireless telegraphy rested with Hertz's discovery of the copper 

 ring detector, its utility for commercial purposes would have been 

 very limited — in fact, nil, since the utmost distance at which signals 

 can be detected by that device is about 8 or 10 feet. It might now 

 be said that while improvements in the construction of the filings 

 coherer, together with increased height of the vertical wires and an 

 increase in their number and in the power of the transmitting appa- 

 ratus, render it possible to receive signals with this form of detector 

 at a distance of 400 to 500 miles under favorable conditions, still, had 

 there been no other receiving instrument than the filings coherer, 

 important as the impnwement in that instruuient has been, there 

 Avould perhaps have been little or no progress to note relative to the 

 speed of transmission by wireless telegraphy, which, with the filings 

 coherer as a receiver, may be placed at from eight to tAvelve words per 

 minute. The action of the filings coherer is inherently sluggish in the 

 production of perfect signals, the cohering and " tapping back," 

 added to the intertia of the moving parts of the tapper, the relays, 

 etc., all tending to that result. 



It may be noted in this relation that in ordinary shipboard prac- 

 tice to-day the distance signaled with the filings coherer does not 

 much exceed 50 miles. 



It was therefore very obvious to all concerned in the art of Avire- 

 less telegraphy that a thing nnich to be desired Avas the invention or 

 discoA'ery of a coherer or detector Avhich Avould, so to speak, " close " 

 autouiatically ou the occurrence of electric oscillations and " open " 

 automatically Avhen the oscillations ceased, oi* vice A^ersa. As fre- 

 quently happens in such cases, this desideratum, an autocoherer, was 

 not A^ery long in forthcoming. 



One of the first devices that bore promise of fulfilling the foregoing 

 requirement is knoAvn as Schaefer's " anticoherer.'' This consists 

 of a silver film deposited on glass. Across this film slits are traced, 

 these being coA^ered by a thin layar of celluloid. When the silver film 

 is made part of an electric circuit it is found that the resistance of the 

 circuit rises Avhen electric oscillations are set up therein, and Avhen 

 the oscillations cease the resistance automatically falls. This action, 

 it Avill be observed, is the reverse of Avhat occurs in the Branly filings 

 coherer: hence the term anticoherer. It has }«H»n surmised that the 



