280 PROGRESS IN WIRELESS TELEGRAPHY. 



same time to and from the same stations. By tuning is meant giving 

 the respective transmitting circuits a fundamental period of oscilla- 

 tion, which can be done by proper adjustment of the capacity and in- 

 ductance of the oscillating circuits, analogously as the rate of vibra- 

 tion of a tuning fork may be varied by varying its elasticity, its 

 inertia, etc. Thus far it does not appear that this desirable result has 

 been satisfactorily accomplished. Jiy means of tuned circuits, how- 

 ever, the i^rinciple of sympathetic resonance is brought into use, and 

 thus, with a given amount of electrical energy at the transmitter and 

 a detector of given sensitiveness, it is feasible to transmit messages to 

 a greater distance than would be the case with untuned circuits. It 

 may be added, also, that Fessenden, De Forest, and others have suc- 

 ceeded very well in cutting out interference from other stations by 

 means of tuning devices. 



For long-distance transmission, Marconi, De Forest, and others 

 have successfully resorted to the u.se of dynamo machines for the 

 production of electric oscillations of much greater energy than are 

 obtainable by the most powerful induction coils. The height and 

 number of vertical wires used in long-distance transmission have 

 also been increased, towers 250 feet high, Avith 50 or more vertical 

 wires, being employed by several of the wireless telegraph companies. 



Considerable progress has also been made in telegraphing over- 

 land without wires, by means of portable outfits, for militarj^ pur- 

 poses, much of the work of this kind having been done by Sie- 

 mens & rialske, of Berlin, Germany, using the Braun system. The 

 apparatus is transported on carts, and the vertical wire is elevated 

 by means of a captive balloon, or, in fair weather, by kites. The 

 distance to which signals can be transmitted by this apparatus is 

 said to be 60 miles, and it is anticipated that within a short time 

 all the important armies of the world will be supplied with apparatus 

 of this general type. Recent experimouts by Marconi and Slaby- 

 Arco in Europe, and by De Forest in the United States, have shown 

 that it is possible to transmit wireless signals to distances of from 300 

 to 1.000 miles overland. 



The most iuiportant connnercial use to which this art has yet 

 been put, however, is that of making possible communication between 

 vessels at sea and between vessels and the mainland, which would 

 still appear to be its greatest sphere of usefulness, and every week 

 sees a larger number of vessels and shore stations equipped with wire- 

 less telegraph outfits. 



