174 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



virtually unlimited number of combinations and be practically free 

 from atmospheric disturbances. Plate 1, fig. 2, shows a type of group 

 tuner. 



FURTHER DEVELOPMENT OF DAMPED WAVE-COHERER METHOD. 



Marconi, by 1898, had carried the development of the filings coherer 

 to its maximum point. 



Lodge in 1897 '^ had disclosed the open secondary circuit for 

 receiving. 



Marconi in 1898 ^ greatly improved this by adjusting the length 

 of the secondary so as to tune it, and by the aid of this improvement 

 was enabled to telegraph a distance of 35 miles « in October, 1899. 



Lodge in 1902 '' invented what is perhaps the most perfect form of 

 coherer, consisting of a thin steel disk dipping in oil-covered mercury 

 and automatically decohered by being kept in continuous rotation. 



A number of self-restoring coherers, of which the Brown ^ carbon 

 coherer may be taken as a type, including the mercury carbon coherer 

 of Solari, came into more or less extended use, and also modifications 

 of the imperfect contact receiver of Neugschwender.^ 



The small progress made along these lines is to be explained by the 

 fact that the damped wave-coherer system is essentially and funda- 

 mentally incapable of development into a practical system. 



Later Developments (Period 1902-1908). 



Progress in Europe since 1902 has been marked by the gradual 

 abandonment of the elements of the damped wave-coherer system 

 and the substitution of elements of the sustained wave nonmicro- 

 phonic contact type. 



In 1900 «' Marconi substituted for the plain aerial an aerial with 

 the writer's tuned local circuit or tank circuit for sending, thus ob- 

 taining a considerable increase in range of transmission. 



In 1902 Marconi invented a very ingenious form of current-oper- 

 ated receiver, called the magnetic detector,'' and with this combination 

 achieved some very remarkable results. 



« Lodge, Great Britain jiatent No. 11575, May 10, 1897. 



6 Marconi, Great Britain patent No. 1232G, June 1, 1898. 



"Official report United States Navy of test U. S. S. Massachusetts, October, 

 1899. 



<* Lodge, Muirhead & Robinson, Great Britain patent No. 13521, June 14, 1902. 



^ Brown & Neilson, Great Britain patent No. 28955, December 17, 1896. 



f A. Neugschwender, Wied. Ann. der Pliysil^, 1899, voL 67, p. 430. Seliaefer, 

 British patent No. 6002, 1899. 



-'' Marconi, Great Britain i)atent No. 7777, April 26, 1900. 



'' Marconi, Great Britain patent No. 10245, 1902. 



