212 , Mr. 0. Heaviside on the Speed of Signalling 



Later on the same instruments were introduced between 

 London and Amsterdam, on a circuit consisting of a land-line 

 of 130 miles on the English side, then a cable of 120 miles, 

 and on the Dutch side a land-line of 20 miles (Culley, Journ. 

 Soc. Tel. Eng. vol. i.). In this case the maximum speed ob- 

 tained was 50 per cent, higher from Amsterdam to London 

 than vice versa. Again, on the London-Dublin circuit, con- 

 sisting of cable 66 miles and land-lines 266 and 10 miles, the 

 longer line being on the English side, the speed from Dublin 

 to London was double that obtained in the reverse direction, 

 viz. 80 and 40 words per minute respectively. Similarly be- 

 tween London and Belfast. 



In all these cases it is to be observed that the station nearest 

 the cable receives the most slowly, and that the greater the 

 inequality of resistance of the land-lines, the greater is the dif- 

 ference in the working-speeds. This seems to point directly 

 to the conclusion that the uncentrical position of the cable in 

 the circuit actually causes the retardation to be greater in one 

 direction than in the other. The fact that the cable receives a 

 much larger charge of electricity when the battery is connected 

 to the end of the shorter than to the end of the longer land- 

 line might, on a cursory examination, seem to corroborate this 

 conclusion. But when the light of theory is thrown upon this 

 view of the matter it is at once found to be untenable. 



It is easily shown that if condensers be distributed in any 

 arbitrary manner along a line which is to earth at each end, 

 dividing it into sections having any resistances, and the con- 

 densers be all initially discharged, the introduction of an elec- 

 tromotive force in the first section will cause the current to rise 

 in the last section, in the same manner as the same electromo- 

 tive force in the last section will cause the current to rise in 

 the first section. Furthermore, it may be shown that if leaks 

 he introduced on the line in any arbitrary manner, the same 

 property will hold good. (The differential equation of the 

 current, which is linear and of the same degree as the number 

 of condensers, is the same for the first and last sections ; and 

 the conditions to determine the arbitrary constants are the 

 isame.) Now every telegraph-line, however irregular it may 

 be in its resistance, capacity, and insulation in different places, 

 may be considered as such a system of condensers and leaks, 

 infinite in number if necessary ; whence it follows that on any 

 line there is absolutely no difference in the retardation in either 

 direction, meaning by retardation the time required for an 

 electromotive force at one end to cause the current at the other 

 end to reach any stated fraction of its maximum. Therefore, 

 to account for the facts, which cannot be gainsaid, we must 



