On the Speed of Signalling through Telegraph Circuits. 2 1 1 



The following Table shows the closeness of approximation, 

 (theoretical — observed) -f- observed in each of the foregoing 

 comparisons : — 



I. 



-•00.39 



l«. 



-•0028* 



31. 



0001 



45. 



-0009 



2. 



0197 



17. 



•0001 



32. 



-•0005 



46. 



-•0070 



3. 



-0158 



18. 



-•0006 



33. 



0002 



47. 



-0043 



4. 



0109 



19. 



0019 



34. 



0008 



48. 



-0291 



5. 



-•0014 



20. 



•0006 



35. 



•0050 



49. 



-•0016 



e. 



•0001 



21. 



-0224 



36. 



•0006 



50. 



•0093 



7. 



0033 



22. 



-0013 



37. 



•0000 



51. 



-0023 



8. 



•0074 



23. 



-0012 



38. 



•0000 



52. 



-0025 



9. 



•0000 



24. 



•0010 



39. 



•0000 



53. 



-0014 



HI. 



•0070* 



25. 



0010 



40. 



•0009 



54. 



-0013 i 



11. 



-0023* 



26. 



iJOOl 



41. 



-0015 



55. 



•0030 | 



12. 



0169* 



27. 



0011 



42. 



- 018 



56. 



-0050 i 



13. 



•0238* 



28. 



0039 



43. 



—•0038 



57. 



-0008 ! 



14. 



•0319* 



29. 



0019 



44. 



-•0078 



58. 



0014 , 



15. 



•0052* 



30. 



-0010 











XXVIII. On the Speed of Signalling through Heterogeneous 

 Telegraph Circuits. By Oliver HeavisideI. 



WHEN the first trials of speed of working were made on 

 the Anglo-Danish cable, then recently laid (September 

 1868), it was found that a considerably higher speed could be 

 reached in one direction than in the other. The u line " portion 

 of the circuit consisted of a land-line on the English side of 240 

 ohms resistance, then a cable of 2500 ohms resistance and capa- 

 city 120 microfarads, and a land-line on the Danish side of 1250 

 ohms — all approximate. The circuit was completed through 

 a battery of 150 ohms at one end and a Wheatstone's receiver 

 of 750 ohms at the other, the circuit being worked on the 

 earth-to-earth principle, i. e. without condensers. But although 

 the battery and receiver at each end were the same, or nearly 

 so, the maximum speed obtained with Wheatstone's transmitter, 

 making mechanically exact signals, was 40 per cent, higher 

 from England to Denmark than from Denmark to England %. 

 This unexpected result was abundantly confirmed by the sub- 

 sequent experience of every-day practice, which proved the 

 existence of a difference in working-speed in opposite direc- 

 tions varying from 20 to 40 per cent, at different times, mainly 

 according to the state of insulation of the land-lines. 



* According to Herschel. 



t Communicated by the Author. 



X It may be interesting to state the actual speeds obtained on this cir- 

 cuit with different instruments. Morse, 60 to 75 letters per minute; 

 Wheatstone's transmitter and receiver, 90 to 140 letters per minute; 

 Wheatstone's transmitter and Thomson's recorder, 300 to 300 letters per 

 minute : in all cases without condensers. 



P2 



