﻿494 Mr. J. B. Henderson on the Effects of Magnetic 



represents the above series in graphic form, where the ordinates 

 represent resistances and the abscissae field-intensity c 



It will be seen that the curves take a form somewhat 

 resembling an hyperbola with its axis parallel to the resistance 

 coordinate ; and that the rate of increase of the resistance, or 

 the inclination of the curve to the horizontal, diminishes as 

 the temperature increases, so that each curve cuts all the 

 others but not in the same point, as will be made clearer in 

 considering the results from the small spiral. The third 

 columns in the foregoing table give the percentage increase 

 of resistance, and these are shown in graphic form in PL XV. 

 fig. 6. Here the curves all pass through the origin and have 

 a similar form to those described above, the inclination to the 

 horizontal being less as the temperature increases. 



With the large spiral, tests were made for hysteresis of 

 resistance by taking two series at the same temperature, one 

 w r ith ascending values of the field-intensity and the other with 

 descending ; but the results obtained agreed within the limits 

 of observational error, and -so, if hysteresis does exist, it must 

 be of -a small order of magnitude. 



Tests were also made for time-lag of resistance by finding 

 the resistance in zero-field, then, after being placed in a mag- 

 netic field, again in zero ; but no difference could be noticed 

 after times comparable with several seconds. That there is 

 such time-lag after very short intervals of time appears in 

 Lennard's results with the alternating current and telephone, 

 which show that the resistance found in this way is a function 

 of the period of alternation ; and it is also shown by some 

 experiments lately made by Rubens in Berlin to determine 

 if vibrating spirals of Bi wire in magnetic fields could 

 be used for microphonic purposes ; but his results proved the 

 negative. 



In the foregoing results the highest field obtained with the 

 large spiral has been 13,000 C.G.S., that is, over an area of 

 about 268 square millim., and was obtained with the pole- 

 pieces 9 millim. apart, with a current of 30 amperes. In the 

 investigation the current was obtained either from six accu- 

 mulators, or from the Berlin supply-mains at a potential of 

 108 volts. "With the fine pole-pieces fields of 28,000 were 

 obtained with about 10 amperes from the accumulators, and 

 33,000 with about 30 amperes from the mains ; and with the 

 same pole-pieces in H. du Bois's ring-magnet and a current 

 of 45 amperes, a field of 39,000 was obtained. 



Thus there was a full range up to 39,000 C.Gr S. available, 

 and the following table gives the resistance of the small spiral 

 at 18° C. in the full range of field-intensities. 



