HERTZIAN WAVE WIRELESS TELEGRAPHY, 121 



that the electrical time-period of both the two circuits mentioned shall 

 be the same. This involves adjusting the inductance and capacity so 

 that the product of conductance and capacity for each of these two 

 circuits is numerically the same. Instead of employing an oscillation 

 transformer between the condenser circuit and the aerial, the aerial 

 may be connected directly to some point on the condenser circuit at 

 which the potential oscillations are large, and we have then another 

 arrangement devised by Professor Braun (see Fig. 14). In this case, 

 in order to accumulate large potential oscil- 

 lations at the top of the aerial, it is, as we | 

 have seen, necessary that the length of the 

 aerial shall be one quarter the length of the 

 wave. If therefore the electrical oscillations g 

 in the condenser circuit are at the rate of iV _ 

 per second, in other words, have a frequency ^ ^ jT 

 N, the wave-length corresponding to this fre- ^ 

 quency is given by the expression, "j~ A, 7 



f 



3 X lO^yN cms. ^ 



Fig. 14. Beaun's Radiator. 

 mi. o rvin • 1 i -B, battery ; J, induction coll ; 



ihe number 3 X 10 is the value in centi- a', key; s, spark gap; l, in- 

 meters per second of the velocity of the elec- '^"°''^°<=e ^oii; c, condenser 

 tromagnetic wave, and is identical with that of 



light. The corresponding resonant length of the aerial is therefore 

 one fourth of this wave-length, or 3 X 10"/4i\^. Generally speaking, 

 however, it will be found that with any length of aerial which is prac- 

 ticable, say 200 feet or 6,000 cms., this proportion necessitates rather 

 a high frequency in the primary oscillation circuit. In the case con- 

 sidered, viz., for an aerial 200 feet in height, the oscillations in the 

 primary circuit must have a frequency of one and a quarter million. 

 This high frequency can only be obtained either by greatly reducing 

 the inductance of the primary discharge circuit, or reducing the capa- 

 city. If we reduce the capacity, we thereby greatly reduce the storage 

 of energy, and it is not practicable to reduce the inductance below a 

 certain amount. 



Summing up, it may be said that there are three, and as far as the 

 writer is aware, at present only three, modes of exciting the electrical 

 oscillations in an aerial wire. First, the aerial may itself be used as 

 an electrical reservoir and charged to a high potential and suddenly 

 discharged to the earth. This is the original Marconi method. The 

 second method, due to Braun, consists of attaching the aerial to some 

 point on an oscillation circuit consisting of a condenser, an inductance 

 coil and a spark gap, in series with one another, and charging and 



