302 Mr. A. A. C. Swinton on High Frequency Discharges. 



pointed towards one another, with an intervening space of 

 about a quarter of an inch. In this space was placed a sheet 

 of glass of sufficient size to prevent sparks passing round its 

 edge, the whole arrangement being such as to form a con- 

 denser of which the points of the two wires were the con- 

 ducting plates and the glass the dielectric. On the coil being- 

 put in action sparks spread out on each side of the glass so as 

 to cover a circle about three inches in diameter, and the lamp 

 filament immediately became incandescent. The capacity of 

 a condenser of this description must be exceedingly small, 

 even if we consider the acting surface to be represented by 

 the whole area covered by the sparks, consequently, though 

 the frequency is of course enormous, the actual quantity of 

 electricity passing in the circuit must be very minute. 



With reference to the heating-effect of very small high- 

 frequency currents, the Hon. Charles A. Parsons has suggested 

 to the writer the following explanation : — 



The total heat imparted to a wire is proportional to the 

 average drop in volts between its ends multiplied by the total 

 quantity of electricity passed, i. e. } by the number of coulombs. 

 This follows from the usual formulae 



E = CR; Heat = C 2 R=CE 9 



Eliminating time we have 



Heat=QE. 



Now if the volts be increased the quantity required to 

 produce a given number of heat-units is proportionately 

 diminished. 



If a 100-volt incandescent lamp taking • 6 of an ampere be 

 brought to incandescence by short impulses of current at 

 10,000 volts average pressure during each impulse, the quantity 

 passed in any considerable time will be only *01 of that which 

 would be required were the 100 volts continuously applied for 

 that time, or will be equal in quantity to "006 ampere con- 

 tinuous current. 



This may be expressed in another way. Assuming the 

 resistance constant we have 



Quantity Q = ^Cdt, 



Heat varies as fC 2 ^. 



If in fig. 2 the ordinates represent the current, abscissse time, 

 then the area of the figures = Q =§Cdt, the heat= fc 2 dt = the 

 moment of the figures about the line Ot. Figures of peaky 



