CHANGE OF ELECTRIC RESISTANCE OF NICKEL. 



541 



Dividing the numbers in each column by the corresponding resistance of the 

 unmagnetised wire and multiplying by 100,000, we obtain the following increments of 

 resistance due to the magnetisation of wires of nickel, the resistances in the unmagnetised 

 condition being 100,000 ohms at each temperature. In the second column of this table 

 the values of the magnetic fields in the heart of the coils are also given. 









Increments of Resistance of 100,001 



ohms of 





Current. 



Field. 





Wire M 





Wire N 









At 12° "6. 

 777 



At 57° -5. 



At93°-1. 



At 12° -9. 



At 57° -4. 



At 93° "9. 



1-5 



696 



807 



793 



732 



793 



818 



14 



65 



739 



762 



781 



693 



735 



766 



1-3 



60-3 



701 



725 745 



648 



690 



711 



1-2 



557 



659 



685 



706 



603 



646 



668 



M 



51 



616 



637 



067 



556 



598 



620 



l-o 



464 



571 



589 



622 



503 



546 



568 



•9 



41-8 



525 



541 



573 



456 



487 



516 



•8 



374 



462 



489 



521 



400 



436 



457 



■7 



32-5 



402 



434 



466 



346 



376 



399 



•6 



27-8 



339 



368 408 



284 



311 



331 



•5 



23-2 



275 



296 332 



223 



245 



268 



4 



18-6 



202 



215 245 



161 



176 



196 



•3 



13-9 



118 



132 156 



97 



108 



121 



•25 



11-6 



76 



89 108 



67 



77 



*0 



The general results embodied in these tables may be gathered at a glance from the 

 graphs on page 542, in which, however, the curves for the intermediate temperatures 

 are not given. A slight inspection of the numbers shows that the omitted curve lies 

 exactly between the other two for the same wire. 



Thus it appears that up to a temperature of 100° C. the effect of rise of temperature 

 is to increase the total change of resistance due to the application of a given field. 



It will be noticed that in the case of the wire M, the increase of resistance in the 

 field, 69*6, is somewhat less at 93°4 than at 57°"5. But the exception is only apparent, 

 and is due to an error of observation which is unavoidable under the conditions of the 

 experiment. It is this same error which gives the different forms to the M and N 

 curves in the higher fields. The curves for the M wire become distinctly more convex 

 upwards as the field attains its higher values, whereas the curves for the N wire tend 

 rather to become concave. Now it must be remembered that the two nickel wires were 

 cut originally from the same piece and had been subjected throughout their history to 

 the same treatment. Nevertheless they did not behave exactly the same as regards 

 their rate of heating when a given current was passed through the surrounding coils. 

 Because of some slight difference in the winding and the general form of the coils, the 

 one wire heated more quickly than the other. Hence when a strong current was used 

 and passed round the wires so as to magnetise neither, a gradually growing deflection 

 was obtained on the galvanometer. Similarly, when the current was broken, the one 



