for Voltaic Electricity, 



201 



The wires of iron and copper on parallel lines were said to be 

 of the same gauge, but the micrometer showed them to be of very- 

 different diameters. This table does not coincide with the law 

 of the conduction of wires of different diameters being as the 

 squares of their diameters. 



Power of hydrogen to abstract the heat produced by the passage 

 of electricity. 



Battery power 410. Current through steel wire 175 hundredths 

 of an inch. 

 Quantity conducted. 



220 . wire red-hot in air. 



310 , in hydrogen,, and invisible in the dark. 



In this experiment battery power not observed. 



Same wire as above. 



In air red-hot .... 220 

 In current of air, quite cold 270 



It would appear that the heating power of a current of electricity 

 diminishes the power of conduction; also that hydrogen, by 

 absorbing the heat, has the same effect as a current of cold air. 



Table V. — No. 20 wire placed in the air-bulb of sulphuric acid 

 thermometer. 



These experiments, very tedious and difficult to conduct, do 

 not appear to indicate any particular law. 



Much in this department of electricity appears yet to be done 

 before we are able to define the laws of conduction, and there 

 are many difficulties to be encountered. It is almost impossible 

 to get wire of any length of equal thickness and texture. It is 

 also not easy always to obtain the same connexions, and the least 

 variation in this respect vitiates the experiments. Some of the 

 anomalies in the tables are to be traced to these causes. 



A difference of temperature also, it appears, will affect con- 

 duction. Even bending the wire with so delicate an instrument 

 as the torsion galvanometer will affect the experiment; and 

 twisting will alter its powers permanently. 



