SUPERPOSED MAGNETISMS IN IRON AND NICKEL. 



199 



Joule further discovered that when the tension exceeded a certain value, 

 there was contraction instead of extension in the direction of magnetisation. 

 This ought to give in these experiments a reversed twist under tensions higher 

 than this critical value. Of this, however, there was no indication, although 

 the thicker iron wire broke under a tension of 2600 grammes' weight, and was, 

 therefore, subjected in experiments A to a comparatively high tension. 



It remains now to consider nickel. The experiments were conducted in 

 precisely the same manner as in the case of iron. The following are the 

 tabulated results for a nickel wire of cross section, -0056 sq. cc, length 36 cc, 

 and tension 1950 grammes' weight ; first, for a steady linear current and varied 

 helical current, and second, for a steady helical current and varied linear cur- 

 rent. As before, the currents are in amperes, and the twists in radians x 10 5 . 



Group A. (Linear Current Steady.) 

 Experiment I. Linear Current = - 674 Amp. 



Helical Current, 



0-368 



0700 



1-210 



1-891 



2-303 



2-616 



3-016 



3-997 



Twist, 



109 



200 



429 



765 



952 



1077 



1206 



1458 



Experiment II. Linear Current == 0995 Amp. 



Helical Current, 



0-307 



0-410 



0-741 



1-276 



1-680 



2-084 



2-594 



5-384 



Twist, 



55 



103 



281 



570 



871 



1052 



1303 



1897 



Experiment III. Linear Current = 2 - 510 Amp. 



Helical Current, 



0-368 



0-700 



1-210 



1-891 



2-303 



2-616 



3-016 



3-997 



Twist, 



152 



263 



596 



1119 



1415 



1923 



2145 



2552 



Experiment IV. Linear Current = 3-039 Amp. 



Helical Current, 



0-205 



0-393 



0-741 



1-313 



1-726 



2-084 



2-594 



3-591 



5-384 



Twist, 



90 



74 



436 



948 



1310 



1553 



1894 



2345 



2819 



