380 



PROFESSOR KNOTT ON SOME RELATIONS BETWEEN 



Table I. — Iron Wires — continued. 



No. 3 (continued). 



No. 4 (continued). 



No. 5 (continued). 





T 



io 4 -e 





T 



io 4 -e 





T 



lO 4 -0 





2050 

 2241 

 2505 



•58 

 •53 

 •53 





814 

 1097 

 1345 

 1625 



1876 



170 

 1-60 



1-22 



1-06 



•96 



C = 2-47 

 H=113 

 H'= 8-37 



23 



403 



784 



1164 



1551 



1931 



2-58 

 213 

 1-78 

 1-39 

 108 

 •93 



C =1-6 



H =8-9 

 H' = 77 



48 



243 



439 



633 



864 



1058 



1251 



1413 



1661 



2050 



2241 



2505 



2894 



316 



2-80 



2-39 



217 



1-69 



1-52 



1-33 



1-20 



101 



•77 



•65 



•68 



•53 



C = 2-07 

 H=120 

 H'= 8-25 



31 



284 

 561 

 814 

 1097 

 1345 

 1625 

 1876 



243 

 2-33 

 215 

 1-91 

 1-70 

 1-46 

 1-30 

 112 



No. 6. r = -072. 





T 



io 4 -e 



C = 2-28 

 H=10 

 H'= 6-33 



20 



280 

 536 



794 



1-79 

 1-59 

 1-39 

 112 



No. 5. r = -059. 



C = 3-04 

 H=116 

 H'= 8-44 



15 



270 



527 

 784 



1-88 

 1-68 

 1-46 

 1-22 



No. 4. r=0502. 





T 



1O 4 '0 



C =152 

 H=87 

 H' = 515 



23 



41 



591 



797 



981 



1180 



232 

 1-78 

 1-39 

 1-86 

 117 

 102 





T 



1O 4 "0 





C = 15 

 H=123 

 H'= 6 



31 



284 

 561 



221 

 213 

 1-91 









A careful study of these numbers seems to lead to the following conclusions : — 

 1. Other things being the same, the twist is greater in the thinner wire. It should 

 be noted here that there is considerable difficulty in deciding as to the meaning of " other 

 things being the same." The best mode is clearly, not to take the current through the 

 wire as a guide, nor yet the current density, but something which may be regarded as 

 giving an approximate estimate of the magnetic effect of the current. I have therefore 

 taken the quantity H', which measures the direct magnetic force at the circumference of 

 the wire due to an axial current of the magnitude used. The method is certainly open 

 to criticism ; but in our absolute ignorance of the magnetic distribution in an iron wire 

 due to a current passing along it, any other approximation could hardly be so justifiable. 

 It will be shown later, that, on the simplest supposition possible, a calculation based on 

 Maxwell's explanation of the Wiedemann effect leads to the result that the twist produced 

 in a thin tube under the influence of given longitudinal and circular magnetising forces 

 is inversely as the radius. It will readily be granted, when all the conditions are taken 

 into account, that the experimental result just given is in fair accordance with the result 

 deduced from theory. 



