476 Superposition of Mechanical Vibrations on Magnetization. 



could either be passed directly through a long iron wire, 

 0*041 cm. diam., or through a coil surrounding* it. In both 

 cases the effects of these oscillations, when superposed under 

 the A and also under the B conditions, were essentially the 

 same as the effects of mechanical vibrations. Any of the 

 corresponding curves of figs. I. and it. (present paper) show 

 the results obtained with sufficient accuracy. 



The precise method in which oscillations are generated 

 does not appear to be material, and I should like to point out 

 wherein Dr. Eccles's experiments differ essentially from my 

 own. He states that he found it possible " to get over and 

 over again practically the same magnetometer deflexion for 

 every spark, provided the effect of previous oscillations was 

 wiped out by taking the iron through a cycle." The fact 

 that the observations could be repeated does not prove that 

 the effect of previous oscillations had been wiped out. The 

 cycle so obtained and upon which the sparks are superposed 

 is not symmetrical about the origin, its want of symmetry 

 being determined by the set given to the magnetization by the 

 preceding oscillations. Moreover, I found, previous to deter- 

 mining my own experimental methods under the A conditions, 

 that repeaied reversals of the cyclic field were not sufficient to 

 wipe oat the effect of immediately preceding oscillations, and 

 that to do so the magnetic metal must be demagnetized by 

 decreasing reversals after each superposition of an electric 

 oscillation or of a mechanical vibration. 



The results are recorded " as if the observations had been 

 taken only on the ascending half of the hysteresis curves." 

 The readings are all positive, and one of the conclusions 

 arrived at is as follows : — " It is evident, moreover, that the 

 magnitude of the effect at any point is closely connected with 

 the slope of the hysteresis curve/' The occurrence of a 

 neutral point, now well established after a cyclic extreme is 

 departed from and which may occur close to the vertical axis, 

 disposes of any connexion between the value of dB/dil 

 at any point and the magnitude of the spark effect. 



Dr. Eccles's experimental method reproduces to a certain 

 extent the working condition of the first form of Marconi's 

 magnetic detector, and confirms the latter' s experience that 

 the magnitude of the spark effect is small as a cyclic extreme 

 is departed from. But in neither case are oscillations super- 

 posed upon a hysteresis loop which has not already been 

 modified by the effect of previous oscillations. In neither 

 case are the A conditions fulfilled. 



