Tonju'ratitvc on Magnetic Clnnnu' of Residnnce. 6i>5 



apI>li«Ml ;in<l hmiiovimI, and tlie curve C 'A\v\' tli(> hi<>;;>est load 

 Wl'l kilos had Ihhmi removed. It will be noticed that <tretchinnj 

 lias the ertect of increa-ing the residual change of resistance; 

 while, as shown in tig. 1, the residual change is diminished 

 when the load is on the wire. 



In the course of these experiments it was noticed that the 

 magnetic change of resistance was very different in different 

 specimens of wire. Three specimens of different diameters 

 were tried, the diameters being '35 mm., '21 mm., and 

 •14 mm. In the tiner wires the change of resistance is 

 smaller at low fields and oi'cater at high fields than in the 

 thicker wire. 



In the wire of '14: mm. diameter the change of resistance at 

 the highest field is over 3 per cent. A considerable portion of 

 this difference is removed by heating the wire in the flame. 

 These results are shown by the curves in fig. 3, which give 

 the change of resistance for the three specimens. 



These curves were all taken with the wires unloaded and 

 at a temperature of 15° C. The difference is perhaps due 

 to the strain which the wire undergoes in drawing. 



It will be noticed that the curves for the finer wires are 

 somewhat similar to those obtained by loading the thicker 

 wire, as shown in fig. 1. 



Experiment II. — Tlie Inflnencp. of Stress on the Magnetic 

 Change of Resistance in Iron.. 



The iron wire experimented upon was "32 mm. in diameter, 

 and was connected up as previously described. The results 

 of the measurements are shown by the curves in fig. I. It 

 will be noticed that the effect of stress on the change of 

 resistance is much smaller in iron than in nickel, and that 

 there is hardly any effect at the highest fields. 



The dotted curve in the diagram represents the after-effect 

 of stress, being taken after the greatest load ['l-l'O kilos.) had 

 been removed. This effect is in the opposite direction to the 

 temporary effect of stress, being an increase at all the fields 

 used ; a similar and smaller effect was observed after removing 

 the other loads. In the case of iron there is very little differ- 

 ence between the value of the change of resistance in specimens 

 of different diameters. 



Experiment IIL — Tlie Injiaence of Stress on tJie Magnetic 

 Change of Re-sistance in Platinite. 



This was a specimen of nickel-steel kindly supplied by 

 Mr. T. Agar Baugh. The wire was '3.5 mm. in diameter, 

 and was quite soft. The effect of stress on the change of 

 resistance of this specimen is shown by the curves in fig 5. 

 The highest value of the change of resistance is rather 



