82 K. HONDA. 



Here H and li denote effective longitudinal and circular 

 fields respective!}', both in C.G.S. units. A represents addition- 

 al change of length by circular field. All these changes were 

 measured at a constant temperature of about 25° C. 



Fig. 1 shows that the change of length by circular mag- 

 netization increases at first showly and tiien rapidly. With the 

 further increase of the circular field, the rate of increase becomes 

 gradually less. This result agrees in quality with Knott's 

 calculation. The circular magnetization combined with a constant 

 longitudinal one is always to increase the length which is first 

 shortened by the longitudinal magnetization. In weak circular 

 fields, the curve of the change of length with a constant 

 longitudinal field lies below the cui've with no such field ; 

 but in strong fields, the first curve lies above the second. The 

 point of intersection of these two curves is displaced into a higher 

 field with the increase of the longitudinal. 



6. We shall next pass on to the change of length by longi- 

 tudinal magnetization with a constant circular field. The tube 

 was first demagnetized by reversals, and then the deflections for 

 longitudinal magnetizing currents of different strength were 

 measured. During the experiment, the temperature at the centre 

 of the magnetizing coil was 18.8° C. The tube was then care- 

 fully demagnetized both as regards the longitudinal and cir- 

 cular magnetizations. Then a constant current was passed through 

 the circularly magnetizing coil so that the field strength became 

 null. Owing to the heating of the coil, the tube rapidly ex- 

 panded at first, but usually after an hour or two, it reached a 

 stationary state ; when that state was reached, the measurement of 

 the change of length by longitudinal field alone was commenced, 

 which gave the length change at a higher temperature. After 



