on Heated Iron. . 289 



will be more forcibly attracted towards B, agreeably to the 

 experiments of Professor Barlow. 



Experiment 2. Raise B to a white heat, apply the north end 

 of a pretty strong magnet to C, and the needle will be drawn 

 forcibly towards A. When the part B has sunk to a red heat, 

 the point B will become a stronger north pole than A, and the 

 needle will be forcibly drawn towards B. 



Experiment 3. Raise B to a white heat, as before, apply the 

 south end of the magnet to C, and the needle will be forcibly 

 repelled by A. When B cools to a red heat, it will now be- 

 come a stronger south pole than A, and the needle will of 

 course be repelled from B. 



It is obvious from the two last experiments, that iron heated 

 to whiteness prevents, in a great measure, the decomposition of 

 the magnetic fluid from C to the remote end of the wire at B ; 

 but when raised to a red heat, the decomposition goes on more 

 readily from C to B than it does at the ordinary temperature of 

 the atmosphere. I was now anxious to try whether iron heated 

 to different degrees had similar relations with regard to the 

 electric fluid. To ascertain this^ I had recourse to the following 

 experiments : 



Experiment 4. I heated the knob of an iron poker white hot, 

 and fixed the other end in the prime conductor of a powerful 

 electric machine, and found that I could not, with a smooth 

 brass ball, draw a single spark from the heated knob. When 

 it began to assume a red heat, a rapid succession of small 

 sparks passed between the two balls ; and the sparks gradually 

 struck off at greater intervals and increased in size as the iron 

 cooled. 



I was now about to draw the conclusion, that iron, heated to 

 whiteness, was a very imperfect conductor of the magnetic and 

 electric fluids, when this striking relation, which I fancied to 

 exist, was proved, by the following experiment, to be quite 

 imaginary. 



Experiment 5. I brought the middle of the poker to a white 

 heat, and having placed it in the conductor, found that I could 

 now draw sparks from the cold knob exactly as if the whole 

 had been at the ordinary temperature of the air. It was cu- 



