276 PROGRESS IN WTRET.ESS TELEGRAPHY. 



The art, Iioavcwi', rccoived its most j)()^v^M•ful impetus ^vhen ISIar- 

 coni, in 1898. iisiiio- vertical wires SO to 100 feet high at each station, 

 a 10-inch spark inchiction coil, and an improved l^ranly-T-iodge co- 

 herer, succeeded in transmitt ing wireless signals a distance of about 

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

 higher vertical wires and more improved apj)aratus, he increased to 

 i^80 miles over water. 



The writer on other occasions has remarked that had the progress 

 of wireless telegraphy rested with TTert^^'s discovery of the copper 

 ring detector, its utility for connnercial i)urp()ses 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 noAv 

 be said that Avhile imi)r<)vements in the construction of the filings 

 cohei-er, togethei- with increased height of the vertical wires and an 

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

 ratus, render it i)ossible to receive signals with this form of detector 

 at a distance of 400 to 500 miles under favoi-able conditions, still, had 

 there been no other receiving instrument than the filings coherer, 

 imi)oi"tant as the iinprovement in that instrument has been, there 

 would perhai)s Inne been little or no pi-ogress to note relative to the 

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

 coherer as a receiver, nuiy be ])laced at from eight to twelve words per 

 minute. The action of the filings cohei-er is inherently sluggish in the 

 production of jierfect signals, the cohering and '' tai)iMng back," 

 added to the intertia of the moving parts of the tapi)er, the relays, 

 etc., all tending to that result. 



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

 tice to-day the distance signaled with the filings cohei'er does not 

 much exceed 50 miles. 



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

 less telegrai)hy that a thing much to be desired was the invention or 

 discovery of a coherer or detector which would, so to speak, " close '' 

 automatically on the occurrence of electric oscillations and ''open" 

 automatically when the oscillations ceased, or vice versa. As fre- 

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

 not vei'v long in forthcoming. 



One of the first devices that bore j)romise of fidiilling the foregoing 

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

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

 these being covered by a thin layer of celluloid. A\'hen the silver film 

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

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

 the oscillations cease the resistance automatically falls. This action, 

 it will be observed, is the reverse of what occurs in the Branly filings 

 cohei"ei': hence the term anticoherer. It has 1>c(mi sui'mised that the 



