192 Mr. J. J. Waterston on the Thermal Action 



for granted — viz. that in the voltaic circle electricity circulates 

 in the mass of the wire through every part of its transverse sec- 

 tion, and is not confined, as with common electricity, to the sur- 

 face only. Professor Ohm's formula, however excellent as a 

 guide in practice, is only empirical ; and although one of the 

 terms is the transverse section of the wire, the accuracy with 

 which it applies to the various conditions of a circuit is no proof 

 of the electric current acting directly upon the interior of the 

 wire. Heat simply is produced in the wire, which may or may 

 not be first wholly engendered upon its surface. If on the sur- 

 face alone, conduction would immediately convey it into the 

 interior; so that there is absolutely nothing to indicate the 

 exact locale of the primary thermal action, whether it takes 

 place on the surface alone, or whether in the interior alone, or 

 in both. 



Barlow and Harris have proved that the power of magnets 

 resides on their surface, and, of course, inductively in the space 

 exterior to that surface. What if this should also be the case 

 with the current-force in a submarine cable ? would it not lead 

 to the adoption of flat conductors ? would not a strip of silver- 

 leaf or copper-foil T V tn °f an mcn * n Drea dth conduct as well 

 as the wires of the Atlantic cable ? Theoretical considerations 

 lead me to believe that it would, and that with a strip half an 

 inch in breadth we should have a conductor equal to a wire of 

 nearly half an inch diameter. Ample surface of conduction 

 with corresponding low electromotive force (or, as it may other- 

 wise be expressed, low electric pressure) seem to be essential to 

 the permanent success of long submarine cables ; and as strength 

 of core is not required, it seems to me that the riband form of 

 conductor might well deserve a trial by those practically inter- 

 ested in the question. 



The calorific effects of discharges of static electricity and of 

 dynamic or voltaic electricity through wires of various gauges 

 have both been fully examined experimentally. It will not be 

 disputed that in the former the primary thermal action takes 

 place only on the surface of the metal. Now the law of this 

 with reference to wires of different diameters has been deduced 

 from Professor Riess's experiments, and is thus stated at page 224 

 of the second volume of De la Rive's Treatise : — " We may there- 

 fore consider the following law as being well established : When 

 the same quantity of electricity completely discharged in the same 

 interval of time traverses wires of the same nature but of different 

 diameters, each wire experiences an elevation of temperature inde- 

 pendent of its length, and inversely proportional to the fourth power 

 of its radius. 33 



The quantity of material in an inch of the thicker wire is 



