160 ANNUAL OF SCIENTIFIC DISCOVERY. 



elapsed, and continued flowing out seven seconds after contact with the 

 battery had ceased ; that with the ordinary telegraphic systems sucli a 

 wire would require 15 seconds of time to make each signal ; and as several 

 signals are required for a letter, only one average word could he trans- 

 mitted per three minutes. Mr. Varley showed that, with the submarine 

 and subterranean wires between Holland, London, and elsewhere, the 

 Bain and Morse instruments would work too slow for commercial 

 purposes ; but, with the aid of his apparatus, these wires are now and 

 have been working for six months at the required speed, viz. : 25 words 

 per minute, for which 300 alterations of current per minute are required. 

 The effect of the former two telegraphs with these wires, when working 

 fast, is to run all the marks together, because the first electric impression 

 has not been completed when the second is given ; but his apparatus, by 

 spilling the charge and reversing the current at every movement of the 

 key, produces rapidly alternating currents through the wire, which, though 

 very weak at the extreme end of the wire, are quite sufficient to actuate 

 his galvanometer relay, which actuates a local battery to produce the 

 marks. The little arm on the axis of the relay, instead of striking against 

 a dead stop, rubs obliquely against a gold spring, filing off the little film of 

 air which would otherwise prevent the instant completion of the local 

 circuit. So sensitive is this apparatus, that four elements of a copper 

 and zinc battery have been found sufficient to work from Manchester to 

 London. He added, " Its advantages over the needle systems are, it 

 requires only one wire, gives a printed record of all communication, 

 requires but one-fourth the power to actuate it, and is not interrupted by 

 comparatively defective insulation. It gains these advantages : 1st. By 

 discharging the line wire at every move of the key. 2d. Gravity aiding 

 the electricity in making the relay contact, thus using the same instead 

 of the difference of the forces. 3d. The sliding action of the relay contact, 

 by rubbing off the thin film of air, gives sure and instant contact with a 

 small amount of battery power. 4th. It will work through a considerable 

 amount of leakage from one wire to the other, because there is a curren t 

 always flowing through the wire, rendering this apparatus peculiarly 

 adapted for wires suspended in the air, and which leak from one to the 

 other in damp weather, the surfaces of the intended insulators becoming 

 coated with moisture." 



The following are Mr. Varley 's conclusions : 1st. If a wire could be 

 suspended in an unbounded non-conductor, or atmosphere with 110 con- 

 ducting body near it, the transmission of an electric current through it 

 would be instantaneous, no matter what may be the length of the Avire. 

 2cl. The approach of any conducting body to this wire would (by 

 induction) reduce the speed of the transmission, as shown in the 1,500 

 mile experiment. 3d. In the case of a wire covered with a non-conduct- 

 ing substance, (such as gutta-percha,) the induction decreases in the same 

 proportion that the thickness of the coating is increased. 4th. The con- 

 ducting power of a wire is in proportion to its substance, the induction in 



