means of obtaining Continuous' Electrical Oscillations. 263 



Now u = 3 x 10 10 cms./sec. = nX 



is the velocity of radiation. 



In the above equation, I is the maximum current in 

 electrostatic measure. If A is the ampere value of the same 



A I 



current, then -^ = -. If, then, the oscillations are persistent 



JL\J XI 



and with frequency n } the energy in ergs radiated per second 

 from the antenna is 



W = -^^ — ergs per second ; 

 6Xn 



4w*u I* A9 , 



= 3Qo"p A er & s P er second ; 



= 40tt 2 ^A 2 watts. 

 X z 



For any antenna the ratio of wave-length X emitted to 

 effective length I is a fixed quantity and. approximates in 

 practice for single-wire antennae to 2*5. We have, there- 

 fore, this curious result which does not seem to have been 

 previously noticed, that the power radiated in watts from a 

 linear antenna of any length is given by the expression 

 W = 64A 2 , where A is the maximum value of the current 

 flowing into the base of the antenna. If (A) is the current 

 as read on a hot-wire ammeter inserted at that point, then 



(A) = -y=, and W = 128(A) 2 watts. 



Thus, if such a hot-wire ammeter showed an antenna 

 current of 1 ampere (R.M.S. value), the radiation would be 

 128 watts, and for the same current is quite independent of 

 the height of antenna or the frequency. 



Seeing, then, that open antennae have such enormous 

 radiative power, we can in practical radiotelegraphic work 

 employ very small antenna currents when using persistent 

 oscillations. 



A complete explanation of all the phenomena involved in 

 the Poulsen arc can hardly yet be said to have been reached. 

 It has been shown by experiments made under the Author's 

 direction in the Pender Electrical Laboratory of University 

 College, London, by Mr. W. L. Upson, that the charac- 

 teristic curve or volt-ampere curve for a carbon-metal arc in 

 hydrogen is a curve falling down with a much steeper slope 

 than the characteristic for a carbon-carbon arc in air. 



