1)4 Messrs. K. Honda and T. Terada on the Change of 



other recorded the time by a mean -time chronometer: 

 According to the usual method of time-observation, 6*0 

 consecutive oscillations were employed for the determination 

 or! its period. The first and the last 10 were signalled and 

 recorded ; we thus obtained 10 sets of time records for 50 

 complete oscillations. The mean of these observations gave 

 the period of oscillation, which usually ranged from 10 to 20 

 seconds. Its value may be considered accurate to — of a 

 second. These processes were repeated for a series of 

 successively increasing fields, the demagnetization being 

 of course effected before each experiment. After a series of 

 observations was taken, the experiment at no field was 

 again repeated, and we usually found the result fairly 

 unchanged. 



Since the magnetizing coil was water jacketed, the heating- 

 effect was inappreciable. The magnetizing current was 

 measured both before and after each experiment, and the 

 mean was taken. The current remained fairly constant 

 during each experiment, except in a few cases. 



Though the period of oscillation was long and the oscillating 

 weights were moderately distant from the lower end of the 

 coil, it was necessary to determine experimentally the 

 retarding effect of the Foucault currents, which was liable to 

 be produced in the system vibrating in the magnetic field . 

 For this purpose, a copper wire of the same size as the 

 specimen was oscillated in a number of fields and the 

 corresponding periods w^ere determined. We found that for 

 the periods used in our experiments, the effect was negligibly 

 small. Logarithmic decrements for different fields were also 

 determined: but generally no appreciable change w r as ob- 

 served. In some of the magnetic wires, the damping of the 

 oscillation was found to become slightly faster as the field 

 was increased. But the change of the logarithmic decrement 

 was too small to sensibly affect the period of oscillation, when 

 referred to the equation 



«\ 1 + ***)> 



where T is the actual period of oscillation, T that for no 

 damping, and k the logarithmic decrement. This agrees 

 with the results * by Ignaz Klemencic and H. Tomlinson 

 for iron. 



* Ignaz Klemencic, Wien. Ber. lxxviii. 7 Nov. 1878, p. 8 ; H. Tomlin- 

 son, Proc. Hoy. Soc. xl. p. 447 ; Phil. Trans, clxxix. p. 1 (1888). 



