524 



PROFESSOR KNOTT ON SOME RELATIONS BETWEEN 



As in the case of Table VI., each row of numbers here given belongs to a complete 

 cycle, the character of which varies with the current and the twist, and with the tapping 

 or non-tapping, very much as in the similar experiments with nickel. As illustrations 

 of the character of such complete cycles, I have picked out the following ones, the twists 

 being expressed in fractions and multiples of 77, the currents in amperes, and the 

 intensities in C.G.S. electro-magnetic units. 



Table showing complete Cycles for Iron Wire. 



(1) Current = 1-23. 



(2) Current=l"18. 



Twist. 



Intensity. 



Lag. 



Twist 



Intensity. 



Lag. 



-1 



-328 



-328 







-3 



-284 



-287 



- 3 



-| 



-330 



-295 



35 



-2 



-292 



-295 



- 3 



-i 



-332 



-213 



119 



-1 



-229 



-295 



- 66 



-i 



-324 



+ 27 



351 







+ 240 



-257 



-497 







-290 



'', + 289 



579 



+ 1 



+ 290 



+ 228 



- 62 



+ i 



- 50 



+ 325 



375 



+ 2 



+ 289 



+ 296 



+ 7 



+i 



+ 208 



+ 332 



124 



+ 3 



+ 281 







+! 



+ 295 



+ 332 



37 









+ i 



livi^ + 330 













(3) Current = 1-39. 



(±) 



Current = 1 "39. Tapped. 



Twist. 



Intensity. 



Lag. 



Twist. 



Intensity. 



Lag. 



-1 



-281 



-284 



- 3 



-1 



-356 



-356 







-h 



-275 



-212 



+ 63 



i 



— 2 



-334 



-312 



+ 22 







-187 



+ 125 



+ 312 







+ 6 



- 90 



-96 



+1 



+ 187 



+ 270 



+ 83 



+4 



+ 318 



+ 328 



+ 10 



+ i 



+ 282 







+ i 



+ 359 







No. 1 is for the first specimen of iron wire ; the others are for the second specimen. 

 The representative curves are shown in figs. 1, 2, and 3, PI. V. The curve for the cyclic 

 twisting ±77 (fig. 2) shows distinct positive lagging, while the curve for the cyclic twist- 

 ing ±3 77 is characterised as distinctly by a negative lagging. The arrows in the figure 

 indicate how the curve is to be gone round. Thus, just as with nickel, a high enough 

 twisting produces in iron a negative lagging. Very similar, too, is the effect of tapping 

 as shown in complete cycles (3) and (4), and in their graphs in fig. 3 (PI. V.). The dotted 

 curve is for the case of tapping. In other particulars the conditions of experiment are 

 identical. In this example tapping has had a distinct effect, not only on the form of 

 the cyclic graph, but also on the range of intensities ; and a study of the numbers in 

 Table VI. will show that in the case of iron, tapping has distinctly more effect on the range 

 than in the case of nickel. 



23. Dominating Influence of the After-effect. — The results embodied in Table VII. 

 are partly shown in fig. 4, PL V., in which the march of the lag- area with current is 

 represented for three different twists. In all cases there is a tendency to a maximum as 



