80 Mr. J. N. Hcarder on the Atlantic Cable. 



Secondly, their lengths being equal, their relative resistances 

 will be directly as their mass ; for the wire which requires to 

 have its thickness increased to produce an equal effect, offers the 

 greatest resistance, and is the worst conductor. It is for this 

 reason that when iron wires are used for telegraphic puqioses 

 they require to be very much larger than when of copper. 



By means of this instrument, the Society will recollect that I 

 determined many of the relations between the energy of certain 

 voltaic arrangements and the conducting power of various wires 

 under different conditions ; and though it may aj)pear strange, 

 yet it is a fact, that the results which I obtained and detailed 

 to the Society from fourteen to sixteen years since, would, if I 

 were to publish them now, be quite new to the scientific world. 

 The laws of electro-motive force and resistance have, however, 

 been determined by instruments of a different character, such 

 as galvanometers, voltameters, &c.; and it is satisfactory to find 

 that they con-espond with the results obtained by the present 

 instrument. 



These laws being determined then, their operation in con- 

 nexion with the transmission of electricity through atmospheric 

 wires is, when sources of error are carefully excluded, very con- 

 stant and definite ; but in the action of subaqiieous conductors, 

 a new class of phsenomcna present themselves, in addition to 

 and altogether different from those already refen-ed to. A wire 

 coated with gutta percha and plunged in water, represents a 

 Leyden jar, of great length and small diameter. The wire is 

 tlie inner coating, the gutta percha or other insulating substance 

 is the dielectric, and represents the glass ; and the water is the 

 outer coating. If a coil of wire, insidated in this way, be im- 

 mersed in a tank of water, with its two ends out of the water, 

 we shall have a Leyden jar whose coated surface will depend 

 upon the length and diameter of the included wire ; and if a 

 charge of electricity be communicated to this wire, either from 

 an electrical machine or a voltaic battery, that charge will be 

 retained for a certain time, and the wire may be subsequently 

 discharged, producing effects commensurate with the conditions 

 of the arrangement. I think about ten or eleven years since, I 

 was applied to by an agent of the Gutta Percha Company, to 

 explain the reason why a portion of the charge of a voltaic bat- 

 tery was retained by an insulated wire under the conditions 

 which I have just described ; and I at once referred it to the 

 action of the Leyden jar. About two years subsequently it 

 was submitted to Dr. Faraday, who gave the same explanation. 

 From that moment I foresaw the difficulties which would pre- 

 sent themselves when very long submarine lines should be used ; 

 and these have been constantly experienced, more or less, in all of 



