CONDITION OF THE CURRENT NEVER CHANGES. 79 



trine of investigation, I next proceed to apply it to the analysis of the different pro- 

 cesses, by which a change of tension is supposed to be impressed on an electric cur- 

 rent; and this leads to the consideration of the second proposition : 



271. " That there is reason to doubt whether the processes usually supposed to af- 

 fect the condition of an electric current are ever attended with any such result ; but 

 that, when changes have apparently taken place, it is probable that they may be directly 

 traced either to a disturbance at the place of generation, or to the development of other 

 currents of a different character, the primary current itself remaining unchanged." 



272. It is popularly supposed that if we pass an electric current through a wire of 

 certain length, coiled upon itself, a kind of inductive influence will be exerted, so that 

 the current shall become more and more intense as it goes. Or, if two currents are 

 simultaneously passed into a double helix, they will mutually fortify each other. 



273. (.) A wire, covered with silk, 48 feet long, and arranged as one circular arc, 

 had a current passed through it which produced a deviation of 35 degrees. The same 

 wire was then coiled round a piece of wood, so as to make 155 circumvolutions ; the 

 deviation was still 35 ; and, therefore, no change was impressed on the current. 



274. (&.) A thermal current was passed through a straight wire with the following 

 result : 



22 



The wire was then coiled into a helix, the current passed through it and measured ; a 

 powerful bar magnet was next introduced into the helix, and then a rod of soft iron. But 

 in all these cases the measured numbers were absolutely the same as before. There- 

 fore there is no change impressed on the thermal current, either in relation to quantity 

 or tension, by making it pass along a coiled wire, or by acting on it with a magnet or 

 a bar of soft iron. 



275. (c.) The same experiments were made with a hydro-electric current, and they 

 gave the same results. 



276. (</.) The above-mentioned (i) thermal current was passed along one of the wires 

 of a double helix, and through the other wire a hydro-current was passed, from a single 

 pair of plates; but the tension and quantity remained the same as before. On sending a 

 current of still greater intensity, viz., from a voltaic series of five pairs of plates, the same 

 result was still obtained ; the hydro-current had power enough to decompose water. 



277. (e.) On altering the polar communications, and thereby changing the course of 

 the current, no change whatever in the primary current, either as to quantity or ten- 

 sion, was observed. 



278. It is well known, that by using a long wire as a discharger of a single pair of 

 plates, a spark will be obtained of a much more brilliant character than when the cur- 

 rent passes through a. shorter wire ; it is upon this fact that the flat spiral riband coil is 

 constructed. Many electricians have supposed that the results obtained by this beau- 

 tiful contrivance were partly due to the inducing action of the successive spires, but 

 chiefly to a long and easy conducting channel being open to the current, which gath- 

 ers momentum in its passage. I have already shown that there is no permanent action 



