ART. U).-K. HOXDA AND S. SHIMIZU : 



8. In all previous experiments, the range of the frequency of 

 an intermittent or alternate current \vas very limited ; but in our 

 case, a string alternator" was introducerl for continuously varying 



p tlie period of the 

 current. The arninge- 



ment is shown in the 

 ^ annexed figure. A 



copper wire is hori- 

 zontally stretched ; one of the ends is fixed to a support S, while 

 the other passing over the pulley P is attached to a weight (}. The 

 wire is electrically insulated at the centre R, so that the current 

 through the two mercury cups nij and m., flows in the circuit C. 

 The ])attery currents pass through the two mercury contacts Mj and 

 Mo. The vibration of the string is maintained constantly oscillating 

 by the electromagnet n and s. If the string is set in vibration with 

 a single node at R, an alternate current is produced in the circuit C ; 

 if only one set of batteries is used, an intermittent current is produced 

 in the same circuit. The frequency of alternation or of interruption 

 can easily be varied by the change of length and of tension of the 

 wire, c, and C2 are two condensers with a suitable capacity to 

 diminish the sparks at the mercury contacts M, and M2. 



For the stud}^ of the vibration of a ferromagnetic wire under a 

 varying field, we used Professor Xagaoka's apparatus for the measure- 

 ment of the minute change of length. In the present experiment, 

 the glass fibre in the slit of the collimator was removed and the fine 

 slit illuminated by a gas flame was used instead. The image of the 

 slit, after reflection by the revolving mirror and refraction through a 



1) K. Honda and S. Shiuiizu, Amer. Jour. Sc. 10. 6i, 1900; Phy. Zeitsch. 2 Jahrgang, 

 25.371, 1901. 



