1892.] Magnetisation in Wires carrying Currents. 501 



Table IY. — Nickel Wire, diameter 0'65 mm. 



Magnetic field 

 due to eoil. 

 C.G-.S. units. 



Eetractions in ten-millionths of length. 



With no current 

 through wire. 



With 1 ampere 

 through wire. 



Difterence. 



12 



- -■ 



8 



8 







15 



10 



11 



-1 



19 



15 



15 







28 



25-5 



25 



0-5 



36 



34 



33 



1 



50 



50 



48 



2 



69 



74 



72 



2 



84 



92 



92 







99 



113 



112 



1 



11Q 



134 



133 



1 



350 



164 



162 



2 



175 



178 



178 







209 



196 



194 



2 



256 



217 



215 



2 



330 



241 



240 



1 



Exp. 7. — A current of 1 ampere was passed through the nickel 

 wire, producing a heat elongation of 340 ten-millionths. Taking 

 the coefficient of expansion as 0*0000129, this implies a rise of tem- 

 perature of 2°*6. The retractions of the wire when carrying a 

 current are given in the third column of the table. Remembering 

 that the figures in the second and third columns denote millionths 

 of a centimetre, the close agreement between the two is very remark- 

 able. I have elsewhere* fully described the method of observation 

 adopted, but I may perhaps mention that each number as set down 

 in the table was obtained by the subtraction of two readings, the 

 one taken when there was no current in the magnetising coil, the 

 other when the current was turned on. The former or zero reading 

 was continually changing, owing to small alterations of temperature, 

 the index rarely being absolutely at rest. All the figures were 

 dictated, and when the second experiment was made, I had not seen 

 the results of the first. I may add that the table contains all the 

 observations which were taken in the two experiments. 



Though at first inclined to attribute such small discrepancies as 

 exist entirely to observational or instrumental errors and to infer that 

 the current had no influence whatever upon the contraction, I think it 

 appears pretty clearly from a careful inspection of the differences 

 tabulated in the fourth column that this is not actually the case. Four 

 pairs of observations agree exactly ; once only the retraction with the 



* 1 Phil. Trans.,' vol. 179, A, p. 218. 



