and of Healed Air for Electricity. 181 



charcoal and in the reverse direction; and, if equally trans- 

 mitted, iodine would appear beneath each of the wires placed 

 on the bibulous paper, as actually happens when the circuit is 

 completed by a metallic communication. 



On urging the fire till the flame reached the upper pole, 

 and turning at the same time the machine with moderate ra- 

 pidity, iodine was deposited at one of the wires which rested 

 on the moistened paper, while there was not the slightest dis- 

 colouration beneath the other wire. From the wire at which 

 the iodine was deposited, it followed that the current was 

 transmitted when the pole in the flame was positive, and in- 

 terrupted when the same pole was negative. The direction 

 in which the machine was turned did not produce any differ- 

 ence in the result; but by reversing the poles in contact with 

 the flame and with the charcoal, iodine was deposited at the 

 opposite wire. Here, then, was the most distinct proof of a 

 free path being afforded to an electrical current passing in one 

 direction, while a current, differing only in the direction in 

 which it tended to move, was interrupted. 



When the machine was turned very rapidly, a slight depo- 

 sition of iodine took place at the wire, where there was none 

 when the machine was turned more slowly ; and at the same 

 time a great quantity of iodine was visible around the other 

 wire. Both poles were now introduced into the charcoal 

 flame, and the machine worked rapidly ; iodine was deposited 

 at both wires. When the poles were surrounded to the same 

 extent by the flame, the deposition was apparently similar at 

 each wire; but when one pole was made just to touch the 

 flame, while the other was brought extensively into contact 

 with it, although iodine still appeared at both wires, it was no 

 longer in the same quantity, showing that the current passed 

 more freely in one direction than in the other. When the 

 pole which only touched the flame was positive, the current 

 passed with more facility than when the same pole was nega- 

 tive. 



That the current, whose effects disappeared or were dimi- 

 nished, was actually interrupted and not neutralized by an 

 opposite current developed during the combustion, it was easy 

 to prove by connecting wires of platina with the flame and 

 ignited charcoal and completing tlie circuit through the solu- 

 tion of the iodide of potassium; but no decomposition occurred. 

 The free electricity which Pouillet ascertained to be developed 

 during the j)rocess of combustion exists in too small quantity 

 to produce any chemical effects, and cannot therefore influence 

 the results of these experiments. 



It is ilifficult to discover a satisfactory explanation of this 



