of Danger in Torpedo Experiments. 73 



cell, and a simple test with the galvanometer will show any 

 one who may care to make the experiment that under these 

 circumstances a considerable current passes along the wire. 

 The only difference between this sea-cell and a cell consist- 

 ing of a tumbler of sea- water, with slips of zinc and iron, 

 would be in their internal resistances; the electromotive 

 force would be the same, but the internal resistance of the 

 small cell would be considerable, while that of the sea-cell 

 is inappreciable, and may be regarded as nothing. 



It is easy to see how there may have been this contact 

 between the copper wire of the firing line and the iron bod} T 

 of the vessel. The exposed end of the wire may, for instance, 

 have touched some portion of the vessel, or its metal fittings, 

 metallically connected therewith, and not originally covered 

 with paint, or from which the paint had been removed. 



But I do not say there was such a contact. Indeed, 

 my object in this paper is not to usurp the functions 

 of the Board by investigating the cause of the accident, but 

 to call attention to what may prove a source of clanger, 

 and perhaps of disaster, in similar experiments, conducted 

 under similar circumstances. 



The important question, therefore, is, whether the elec- 

 trical action of a sea-cell composed of a zinc case like that 

 used in the fatal experiment, the body of an iron vessel, and 

 the sea-water in or on which both are lying, is sufficient to 

 produce a current equal to or approaching within dangerous 

 proximity to that which is known to be sufficient to explode 

 an ordinary fuse. 



By r the well-known law called Ohm's law, the electro- 

 motive force in any circuit, measured in Volts divided by 

 the current circulating in the circuit, measured in Vebers, is 

 equal to the total resistance of the circuit, measured in 

 Ohms. Given any two of these quantities, and the third 

 can at once be ascertained. 



Poggendorff (as quoted by Sabine) gives the electromotive 

 force of zinc and iron in a concentrated solution of chloride 

 of sodium (common salt) as — 



•476 of a Daniell's element, 

 = -476 x 1-079 Volt, 

 = -514 Volt. 



From tabulated results obtained by Professors AjTton and 

 Perry, and given in Everett's Units and Physical Con- 

 stants, the value would appear to be '564. It is found 

 thus : — 



