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PROFESSOR KNOTT ON SOME RELATIONS BETWEEN 



the required twist. Only three different specimens of nickel wire were at our disposal, 

 and of these the thinnest one had no special claims to purity. The symbols, r, c, H, H 7 , 

 T, 0, have the same meanings as before, except that H has no reference whatever to 

 a maximum twist. 



r = radius of wire in centimetres. 



C = current along the wire in amperes. 



H = longitudinal magnetic field. 



H' = C/5r = circular magnetic field at the circumference of the wire. 



T = tension in kgs. weight per sq. cm. 



6 == measure in radians of the twist per centimetre length of the wire. 



Table II. — Nickel Wires. 



No. 1. 



r = -0253. 



C = 152 

 H =28-5 

 H' = 12-0 



T 



160 



657 



1155 



1652 



2150 



10 4 -fl 



No. 2. 



r = -0422. 



521 



3-67 

 301 



2-43 

 1-82 



G = 2-28 



160 



6-32 



H =285 



657 



3-87 



H' = 18-0 



1145 



241 





1652 



2-22 





2150 



1-73 





2687 



1-85 



C = 152 

 H=285 

 H'= 72 



io 4 e 



No. 3. r=05. 



57-4 

 236 

 415 

 594 



773 



1-54 

 1-37 

 1-25 

 1-19 

 107 



C = 2-28 



57-4 



1-51 



H=285 



236 



1-45 



H' = 108 



415 



1-45 





594 



1-38 



C = 152 

 H = 285 

 H'= 61 



41 



168 

 296 

 423 

 550 

 736 

 1107 



C = 231 

 H=28-5 

 H'= 9-2 



41 

 168 

 296 

 423 

 550 

 736 

 1107 



1O 4 '0 



1-86 

 2-31 

 256 

 2-64 

 2-47 

 235 

 1-86 



301 

 335 

 3 38 

 3-28 

 315 

 2-67 

 210 



It will be noticed that the thinnest specimen behaves very like iron — that is, 

 increasing tension is accompanied by diminishing twist, and that very markedly. A 

 very similar effect is produced in the case of the intermediate specimen, with the single 

 difference that the effect is not so pronounced. With the thickest, and what is probably 

 the purest specimen, however, the effect of tension on the twist is quite peculiar. At 

 first, as the tension is increased, the twist increases until the tension attains a value of 

 300 or 400 kgs. weight per sq. cm. After this, as the tension is further increased, a 

 pretty rapid decrease of twist sets in. It may be mentioned that this maximum twist 

 for some intermediate value of tension was obtained in my earlier experiments * with 

 very thin nickel wire. It existed, however, only in one series of experiments, and 

 disappeared when the current along the wire was doubled. In the present case there is 



* See page 203 of the paper already referred to. 



