go Relations between Chemical Change, [January, 



pole, and we get a current of electricity, magnetic, and 

 other forces, all brought into play, and we get a good deal 

 of work out of them. Next put them at the poles of another 

 thermo-electric battery composed of metals differing in 

 thermo-electric power from the former battery, and we 

 accordingly get more or less work out of them, as the case 

 may be. Is there any limit to this ? The answer to this 

 question requires proof. 



8. Now to turn to the aspect of the question as presented 

 in a galvanic circuit. Is there any necessary connection, 

 under all circumstances, between the heat evolved and the 

 magnetic force produced ? Do they bear any proportion to 

 each other ? It is often assumed and stated that they are 

 the measures of each other. Let us show that they are 

 not. It is pretty well agreed that i, being the intensity, and 

 r the resistance of the external part of a circuit, H (the heat 

 of the exterior circuit) = i 2 xr. But though many persons 

 have asserted or assumed that other forms of energy vary 

 as the heat, yet I think no one has ventured to maintain in 

 so many words that the force or energy varies as iz x r. 

 Almost any experiment would instantly show that this was 

 not true. What is the mathematical expression for the 

 energy is by no means determined. Quot homines tot 

 sententice. It is pretty well agreed that the action of a wire 

 on a magnetic needle varies as / x i, I being the length of 

 wire. But when we come to an electro-magnet this will 

 not hold. Some say its attractive force on soft iron varies 

 as I 2 x i 2 ; this seems the prevailing opinion, but it is certainly 

 not true ; or, at least, true in exceedingly few cases. 



I have examined and compared more than 1200 ex- 

 periments by different persons ; and though it certainly 

 varies as some function of / and some function of i, yet, 

 under different circumstances, it seems to vary almost as 

 any function of / less than l z , and any function of i less than 

 i 2 . In fact, it seems to vary under different circumstances, 

 according to laws which are as yet almost wholly unknown. 

 But this we may, I think, safely say that it does not vary as 

 the heat. Again, the law which connects the portative 

 power of a magnet with its attractions at various distances 

 is by no means uniform. To show clearly that there is no 

 connection between the heat and other forms of energy in 

 a wire, take the very instructive experiments published by 

 Mr. Gore in the " Philosophical Magazine," of October, 1870. 

 He took two helices of the same length ; one made of 

 platinum wire, the other of copper wire ; he placed them at 

 equal distances from a magnetic needle, and so arranged 



