234 Mr. Albert Griffiths : Some 



the former considerably, while diminishing the latter to a 

 much less degree. 



I employed a length of iron wire which had a resistance 

 equal to 1'845 ohms, £ = 4675 centiin. ; taking //, = 100, we 

 get when p = 2irx 10,000 :— 



r p 2 = *50 approx. 



The wire was placed between the secondary of the induction- 

 coil (which had, as arranged, a resistance of about 24 ohms) 

 and the Wheatstone bridge. 



No very appreciable change was produced in the intensity 

 of the sound of the telephone when the iron wire was intro- 

 duced, nor was any change produced in the reading which 

 gave the position of minimum sound. 



The use of the telephone, as being too comprehensive in its 

 record, seemed to me in some respects unsatisfactory; and I 

 thought that possibly a method might be useful which enabled 

 the telephone to be replaced by a galvanometer, whilst still 

 retaining an alternating current. 



It has already been mentioned that the interruptions were 

 produced by means of a vibrating wire, a platinum point 

 attached to the wire dipped in and out of mercury ; to the 

 same vibrating wire was attached, by means of an insulator, 

 some platinum wire in the form of an inverted U, the lower 

 tips of which just dipped in some mercury contained in 

 two little vessels. The telephone was replaced by a galvano- 

 meter, and the latter was so connected to the bridge that the 

 galvanometer-branch was only complete when the platinum 

 wire (in the form of an inverted U) dipped into the mercury 

 in the two little vessels. 



This arrangement, as was to be expected, gave correct 

 results when the resistance of a german-silver wire, for 

 example, was determined by means of an alternating current; 

 but when the attempt was made to determine the resistance 

 of a bismuth spiral in a strong magnetic field, the method 

 failed. Matters were sufficiently stable to allow of observa- 

 tion s, but the results obtained varied with the frequencies, 

 and even with the same frequency were not constant from 

 hour to hour. Since readings could be obtained, and since 

 Y^ of a second is no doubt small in comparison w T ith the 

 time the galvanometer-branch was complete, it seems ex- 

 tremely probable that the action of the bismuth spiral 

 depends on some action upon the alternating current of the 

 frequency I was endeavouring to employ (about 50). It 

 seems likely also that the action of the bismuth is not a 

 simple one, i. e. there is perhaps not merely (if at all) an 



