168 HOUSTON, KENNELLY — THE PATH OF A CURRENT. [Mar. 19, 



sive arrows, none of which entirely cancel. Their sum, however, 

 is half ei, and at ad, rhe voltage E'.,, E'^^, falls on the dotted lines E'l 

 B', E'\ D'. The same is true for any other point on the line. 

 Consequently, the pressure falls steadily from AC to BD. 



It is otherwise, however, with the magnetic flux which under- 

 goes Ro reversal. The development of this is shown at M^, M^ and 

 Mg. The arrows are all of equal length to the corresponding elec- 

 tric flux arrows at E^, E2 and E3, but there is no reversal of direc- 

 tion. The sum of all these sets of arrows is constant at all points 

 of the line, and this condition of constancy in total magnetic flux 

 is represented by the horizontal straight lines m, m, m, m, m, m. 

 In other words, the current strength is constant. 



The rate at which energy is being transferred from the dynamo 

 along the circuit past any point is simply the sum of the electric and 

 magnetic energies contained in the various passing streams of flux, 

 the summation being made with regard to the direction of these 

 streams. Thus the first stream may carry past the point considered 

 1,000,000 ergs in each second, half in magnetic energy, and half in 

 electric energy, the second stream may carry 500,000 ergs back- 

 ward, the third 250,000 forward, and so on; the resultant stream 

 in this case being 666,667 ^^S^ P^^ second forward, and this is the 

 activity of the circuit at the point considered. 



According to these views, therefore, the electric current, which is 

 electric flux-rush, is invariably transmitted with the velocity of 

 light in the ether of the particular insulator considered. But the 

 actual velocity with which an electric impulse travels along the cir- 

 cuit, as measured by the time which elapses between the connection 

 of the source at the generating end and the appearance of energy at 

 the receiving end, always tends to be less than this velocity, because, 

 owing to attenuation and distortion, the first impulse or block of 

 flux may be completely absorbed and dissipated before it can reach 

 the distant end with the velocity at which it travels, and further 

 flux must gradually come up from the source and suffer attenuation 

 and distortion, before the vanguard can finally arrive at the receiv- 

 ing end and perform its allotted function. It is for this reason that 

 a submarine electric cable between say Ireland and America, takes 

 nearly |th of a second before an electric signal or impulse trans- 

 mitted from one end will make its first appearance at the other, 

 although the time that an electric wave would take to traverse its 

 length would be only say about ■g^o'^h second. The original impulse 



