194 



PROFESSOR C. G. KNOTT ON THE 



reversings and re-reversings of the current, a series of readings was obtained 

 whose differences gave a good mean. From the numbers so deduced the true 

 twist expressed in radians was easily calculated. 



The first experiments were made with an iron wire, '00435 square centi- 

 metres in cross section. The most important are those in which the current 

 along the wire (the linear current) was kept constant, while the helical current 

 was made to vary from under half an ampere to nearly six amperes. Five 

 different series were taken with different values of the steady current. In the 

 following tables the upper row gives the successive values of the helical cur- 

 rents in amperes, and the lower the corresponding twists in radians x 10 5 . 



Group A. 

 Experiment T. Linear Current = "575 Amp. 



Helical Current, 



Twist, 



0-377 



234 



0-741 



489 



1-289 



629 



2-045 



672 



2-573 



663 



5-019 



625 





Experiment II. Linear Current = 



= -723. 









Helical Current, 



0-368 



0-758 



1-289 



1-676 



2-025 



2-436 



2-902 



3-375 



5019 



Twist, 



307 



597 



816 



877 



907 



900 



881 



832 



703 





Experiment III. Linear Current = 



= 1-891. 









Helical Current, 



Twist, 



0-393 



0-741 



372 



762 



1-254 



1-566 



1179 



1335 



1-987 



1389 



2488 



1389 



2-925 



1387 



3-527 



1345 



4-068 



5-781 



1279 



1077 



Experiment IV. Linear Current = 3-157. 



Helical Current, 



0-460 



0-700 



1-254 



1-991 



2488 



3-157 



4-592 



Twist, 



342 



775 



1251 



1567 



1680 



1710 



1652 



