1839.] Telegraphic Signals by induced electricity. 725 



Up to the sixth mile the needles were deflected with great rapidity 

 on the connexion being made with the voltaic element. The reversal 

 of the order of connection also satisfactorily reversed the needle from 

 east to west, and the contrary. But when the deflection fell to below 

 40°, the movements were exceedingly sluggish, so that on an average 

 two seconds elapsed before each signal could be read off. The change 

 of battery poles then often failed in reversing the direction of the 

 needles — and here, as before, at least two seconds were consumed in 

 each movement. Applying the same rule to this as to the preceding ex- 

 periment, the galvanometer would convey signals by a copper wire to a 

 distance of twenty-eight miles — and this might be increased by enlarging 

 the wire or the battery, or by adding to the delicacy of the galvanometer 

 — but in one essential point this system was deficient, namely, in rapi- 

 dity of movement. Two seconds or even one, on each telegraphic 

 movement, would be an extravagant waste of time compared with the 

 celerity with which signals can be conveyed by another method. 



Chemical decomposition. 

 One of the most delicate of all tests of voltaic electrical action is 

 the decomposition of ioduret of potassium and the production of a 

 blue colour which the free iodine strikes with starch. This effect 

 was produced in my experiments for a line of three miles of wire. 

 Beyond this no decomposition could be effected. From this fact we 

 are entitled to infer the impracticability of Soemmering's method. 

 See § 2. 



Induction machine, and mode of correspondence by Pulsations and 



Chronometers. 



The battery was connected with the primary coil see fig. 1. p. 723. 

 by very short wires ; — the ends of the secondary coil wires screwed 

 to the right and left wires of the great parallelogram. P. 721. 



On breaking contact with the primary coil, a shock utterly intole- 

 rable passed at half a mile to an individual holding the metallic 

 handles in which the wires ended. 



To avoid fatiguing details I may at once state, that by this secon- 

 dary coil, excited by but three small voltaic couples, the shocks up to 

 seven miles were exceedingly smart — at eleven and a half at each side, 

 they amounted to no more than strong, but not disagreeable, sensations. 

 I think these might be best termed " pulsations," for to the hand they 

 impart the same feeling proportionately, that a strong and full pulse 

 does to thejinger. 



5 A 



