346 Mr Kemp^s Observations on the Electro- Magnetic 



On the communication being formed with the needle appara- 

 tus, no effect whatever was produced on the needle, showing 

 that charcoal, at a natural temperature, is not capable of con- 

 ducting the electricity of a single pair of plates, so as to affect 

 the needle. 



The cylinder of charcoal was then lowered into the furnace, 

 which was at a high temperature. 



When it had arrived at a red heat, the needle indicated, by 

 its deviation, that the electric current was circulating, and as 

 the temperature of the charcoal increased, the deviation became 

 gradually greater. The piece of charcoal was afterwards raised, 

 till it was brought opposite to the flue of the furnace, into which 

 a strong current of air was passing. Here the charcoal under- 

 went a rapid combustion, and the effect produced on the needle 

 was much increased. 



Experiment W. — Having prepared a cylindrical piece of 

 charcoal (Plate V. Fig. 4.), and coiled round each end of it 

 copper wires, it was placed into a glass tube, A B, of a little lar- 

 ger diameter than itself, to admit of the wire expanding. The 

 ends of the tube were then hermetically sealed round the wires. 

 The communication being made, as formerly, the tube was gra- 

 dually lowered into the furnace, and, when it arrived at a red 

 heat, no effect whatever was produced on the needle. When 

 the furnace had arrived at a high temperature, and the glass 

 had fused around the charcoal, a very slight effect was percep- 

 tible on the needle ; but it did not seem nearly so great as that 

 produced when the charcoal was in a state of combustion — the 

 temperature in both cases being alike. 



It would appear from these experiments, that the conducting 

 power of charcoal depends more upon its undergoing combus- 

 tion, than upon the temperature to which it is raised. 



The following experiments were performed, to ascertain whe- 

 ther or not charcoal, when forming the galvanic circuit, becomes 

 magnetic, like metallic wires, or merely acts the part of a con- 

 ductor, without displaying the phenomena of attraction and re- 

 pulsion. 



The apparatus used in this case consisted of a glass jar, A B, 

 (Fig. 5.) into the bottom of which was placed a magnetic needle, 

 C. It was provided with a wooden cover (Fig. 6.), made to fit 



