164 ANNUAL REPOKT SMITHSONIAN INSTITUTION, 1908. 



Tliis is no mere dream of a visionary philosoplier. All the requisites needed 

 to bring it within the grasp of daily life are well within the possibilities of 

 discovery, and are so reasonable and so clearly in the path of researches which 

 are now being actively prosecuted in every capital of Europe that we may any 

 day expect to hear that they have emerged from the realms of speculation into 

 those of sober fact. Even now, indeed, telegraphing without wires is possible 

 within a restricted radius of a few hundred yards, and some years ago I assisted 

 at experiments where messages were transmitted from one part of a house to 

 another without an intervening wire by almost the identical means here 

 described. 



The statement in the last paragraph of the quotation refers to the 

 work of Prof. David E. Hughes." 



Professor Dolbear also suggested the same thing in an article in 

 Donahoe's Magazine, March, 1893. 



In fact, the idea of using Hertzian waves for wireless telegraphy 

 seems to have been quite widespread in the years immediately fol- 

 lowing Hertz's publications. 



Fairly efficient means of generating electromagnetic waves of any 

 desired length had been made known by Hertz. Vertical antennse 

 connected with the ground had been previously used for sending and 

 receiving by Dolbear in 1882 in connection with his system for tele- 

 graphing by electrostatic induction ^ and also later by Edison and 

 others. 



Hertz's receiver, the minute spark-gap, was not suited for v/ireless 

 telegraphy, and before any telegraphic work could be done a suitable 

 receiver had to be found. 



The fact that tubes containing conducting powders had their 

 resistance altered by the discharge of a Ley den jar and that the 

 original resistance could be restored by tapping the tube was first 

 noted by Mmick. in 1835.'' 



In 1890 Branley showed that such a tube Avould respond to sparks 

 produced at a distance from it.*^ 



In 1892, at a meeting of the British Association at Edinburgh, 

 Prof. George Forbes suggested that such a tube would respond to 

 Hertzian waves. 



In 1893 Professor Minchen demonstrated experimentally that such 

 powders would respond to electro-magnetic waves generated at a 

 distance." He used a battery and galvanometer shunted around the 

 powder to detect the effect of the waves. 



« For report of this work see Electrician, May 5, 1899. 

 ^ Dolbear, United States patent No. 350299, March 24, 1S82. 

 " See Guthe " Coherer action," Transactions of the International Electrical 

 Congress, St. Louis, 1904, p. 242. Munck., PoggendorfE Ann., 1838, vol. 43, p. 193. 

 f^ Branley, Comptes Rendus, 1890, p. 785, and 1891, p. 90. 

 ^ Minchen, Proceedings Physical Society, London, 1893, p. 455. 



