On the relation of Common and Voltaic Electricity. 345 



an amount of mechanical strength to the insulating coating, that, 

 in addition to its improved electrical character, it will be free 

 from the disadvantages before alluded to, when not thus pro- 

 tected. The specific gravity also of such a cable may be made, 

 if necessary, extremely low. 



When made of the requisite dimensions, it need not weigh 

 more than 6 cwt. per mile in air, or 1 cwt. in water; and, from 

 experiments made with a sample of an analogous construction, 

 the breaking strain would be upwards of 17 cwt., or equivalent 

 to between seventeen and twenty miles of its own length in 

 water. It will be remembered that the Atlantic Cable would 

 not support three miles of its own length in water ; and I ques- 

 tion much if the integrity of its gutta-percha coating could be 

 depended upon under the strain of a single mile. 



These are considerations which, I would venture to submit, are 

 of no mean importance, even when viewed apart from any elec- 

 trical qualities, but which, when taken in connexion with those 

 already described, appear to me to give to this form of cable a 

 decided superiority over any form yet devised. I say nothing 

 of any subsequent coating of wire, &c. for additional protection 

 in exposed situations, when found to be necessary, as such an 

 arrangement is as applicable to this form of cable as to any 

 other. 



LIV. Note as to the relation of Common and Voltaic Electricity. 

 By J. J. Waterston, Esq.^ 



IN the seventh series of his ' Experimental Researches,' Fara- 

 day treats of the absolute quantity of electricity associated 

 with the atoms of matter, and sums up with a statement as to 

 the quantity of electricity associated with the chemical elements 

 of a grain of water, which has often been quoted since in a way 

 that tends to mislead as to the potential magnitude of the forces 

 involved. There is an example of this in the last (January) 

 Number of the Edinburgh Review, p. 235, where the following 

 passage occurs: — "Yet they find authority in the marvellous 

 fact, well authenticated by Faraday, that one drop of water con- 

 tains, and may be made to evolve, as much electricity as under 

 other manner of evolution would suffice to produce a thunder- 

 stormP The mechanical value of the chemical force that unites 

 the oxygen to the hydrogen of a grain of water is well known to 

 be about equal to the weight of 7 cwt. exerted through one foot. 

 That such amount of force would suffice to produce a thunder- 

 storm is plainly an idea that cannot be entertained j nor is it 

 strictly implied by the words of Faraday, which arc — " The che- 

 * CoraTOunicatcd by the Author. i 



Phil. Mag. S. 4. Vol. 17. No. 1 15. May 1859. 2 A 



