Measure of the relative Tension of the Electric Current. 273 

 Table A. 



and therefore we infer that the foregoing ratio holds. 



Currents of very low tension give proofs of the same fact. 

 A thermal pair of platina and palladium passed 44 through 

 the primary, and 19*50 through the secondary wire; and 

 when by increasing the temperature 236 passed through the 

 primary, 115 went through the secondary wire. In a pair of 

 palladium and silver, 165 and 11 30 being passed successively 

 through the primary, 43 and 313 went through the second- 

 ary wire. In a pair of iron and platina, 170 and 249 being 

 successively sent through the primary, 79 and 112 respectively 

 passed through the secondary wire. 



But let us further suppose, that the quantity of electricity 

 passing at different times through the primary wire A is con- 

 slant, its tension alone undergoing an increase. If A formerly 

 conducted all that was presented to it, it will under this new 

 condition of things of course still do the same. Such however 

 will not be the case with B, for a greater quantity is now en- 

 abled to pass it than before, and the ratio — will give a 



greater value ; we shall therefore in this case have a measure 

 of the tension. But if the tension still keeps increasing, b will 

 continually approach to equality with a ; and when the ten- 

 sion is infinitely high, these quantities ai'e accurately equal to 

 each other ; or in other words, when the elastic force of a 

 current is infinitely high, its tension is unity. 



If, on the other hand, the tension becomes lower and lower, 

 h continually decreases, and finally might be found equal to 

 zero. The value of the ratio then becomes zero; and there- 

 fore at the two extremes, or where the tension is unity, and 

 where it is zero, the secondary wire, so far from ceasing to act, 

 still truly indicates the condition of the current. 



Whilst, therefore, A conducts freely the whole current, B 

 will measure its tension under all circumstances; but in point 

 of practice, we can never make the adjustment here hypothetic 

 cally indicated, or so arrange a wire A, that it shall conduct 

 all the electricity presented to it. Let us therefore here in- 

 quire, how this variable condition of both wires will affect the 

 result. Let the tension [f], so change by any amount as to 



Phil. Mag. S. 3. Vol. 15. No. 96. Oct. 1839. T 



