HERTZIAN ]YAVE W I HE LESS TEEEGRAFIIY. 561 



resonance. Many devieey of this kiml due to Professor Slaby and 

 others have been suggested and tried l)ut the details are rather too 

 technical to be fully described here. 



It will be noticed that llic Tcceiving aerial may be arranged in one 

 of two ways — it may be oitlK'r earthed at the lower end or it may be 

 insulated. It has been claimed that there is a great advantage in 

 earthing the receiving aerial directly in that it eliminates atmospheric 

 disturbances. 



We shall allude to this point more particularly later on. Mean- 

 while it may be mentioned that the receiving arrangements, as a whole, 

 constitute a sensitive arrangement, as shown by Popoff, Tommasina 

 and by all the large experience of Mr. Marconi himself for detecting 

 changes in the electrical condition of the atmosphere, which are doubt- 

 less of the nature of electrical oscillations. On the other hand, the 

 receiving arrangements may be perfectly insulated, and some experi- 

 mentalists have asserted that by this method 



the greatest freedom is secured from atmos- c |— J— 00-i 



pheric disturbances. Amongst the non- ~T2s^^^^^s^^^~ 



r5~ir"S~5iri5\- 



earthed arrangements the system invented l)y J ^ 



Professor F. Braun, of Strasburg, and worked Hi Ih — - — 



by Messrs. Siemens, of Berlin, may be men- aTrT^r^^-,r,r-jnr-|€iii=>p 



tioned.* ^^ 



Professor Braun 's arrangements are in- fig. 21. braun's nox- 



T , J • ,1 T- • T7I- 01 T ^.^ ■ EARTHED Receiver. J, indue- 



dicated m the diagram m Fig. 21. In this tion cou ; c, c, condensers ; <s, 

 case, an induction coil is used to create a spark gap; ,7, transmitting jig- 

 clischarge between two spark balls, and to finVgs^ube-Xreiayf^, ba^! 

 these two balls are connected the two tery. 

 outer coatings of two condensers, the inner coatings of which are con- 

 nected together through the primary coil of an air core transformer. 

 The secondary coil of this transformer is connected to two extension 

 wires forming a Hertz resonator, and the length of these wires is so 

 adjusted with reference to the time period of the primary circuit that 

 they resonate to it, the whole length from end to end of the secondary 

 circuit being half a wave length. The receiver, as shown in the diagram, 

 consists of a pair of quarter wave length receiving wires connected 

 through two condensers, which are shortcircuited by the primary coil 

 of an oscillation transformer. The secondary circuit of this last 

 oscillation transformer has two extension wires to it, turned in the 

 same manner, to respond to the primary oscillator; and in the circuit 

 of one of these extension wires is placed a coherer tube, shortcircuited 

 by a relay and a local battery. 



It will thus be seen that there is an entire abolition of ground con- 



* See The Electrical Revieir, September 26, 1902, Vol. LI., p. 543. 

 VOL. Lxni. — 36. 



