HERTZIAN WAVE WIRELESS TELEGRAPHY. 



55 





Wf 





V ; 



w 



timed at a certain rate, the bobbin will act like a closed organ pipe to 

 air impulses and oscillations of potential will be accumulated at the 

 opposite end, which have much greater amplitude than the impressed 

 oscillations at the end at which they are applied. We can make the 

 existence of the amplitude oscillations of potential evident by attaching 

 to one end of the bobbin a vacuum tube, which will be illuminated there- 

 by, or by terminating it by a pointed piece of 

 wire, so that an electrical brush can be formed 

 at the point, if the potential variations have 

 sufficient amplitude. We arrange also another 

 closed oscillation circuit consisting of two 

 Ley den jars and a variable inductance coil 

 and a pair of spark balls which are connected 

 ito an induction coil. In this manner we can 

 set up oscillations in the discharge circuit of 

 these Leyden jars, and we can vary the time 

 period by altering the inductance and the 

 capacity. If we denote the capacity of the 

 jars in the microfarads by the letter C and the 

 inductance in centimeters of the discharge circuit of the jars by the 

 letter L, it can then be shown that the number of oscillations per 

 second denoted by n is given by the expression :* 



TcT-rc 



Fig. 22. Seibt's Appa- 

 ratus FOE Exhibiting Elec- 

 tric Resonance. I, induc- 

 tion coil ; S, spark gap ; CC, 

 condensers; L, variable in- 

 ductance; E, earth plate ; W W, 

 wire spirals ; W, vacuum 

 tubes. 



n = 



5, 000,000 

 VCL 



If now we adjust the Leyden jar circuit to a particular rate of oscilla- 

 tion, we have between the terminals of the jar or condenser an alter^f 

 nating difference of potential or electromotive force. If we connect 

 one side of the jars to the earth and the other side to the foot of one 

 of the spirals or bobbins above described, we shall find perhaps that the 

 vacuum tube at the other end is not rendered luminous. When, how- 

 ever, we adjust the inductance in the discharge circuit of the jar to a 

 certain value to make the frequency of the condenser oscillations agree 

 with the natural time period of the bobbin terminated by the vacuum 

 tube, this latter at once lights up brilliantly. Again, if we connect 

 both these bobbins at the same time to the discharge circuit of the 

 Leyden jar, we shall find that we can make an adjustment of the in- 

 ductance of that circuit, such that either of the bobbins at pleasure can 

 be made to respond and be set in electrical vibration, as shown by the 

 illumination of the vacuum tube at its upper end or by an electrical 



* See Cantor Lectures, on ' Electrical Oscillations and Electric Waves,' 

 delivered before the Society of Arts, London, November 26, December 4, 10, 

 17, 1900. Lecture I., page 12, of reprint. 



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