1878.] 



Eleetrodynamie Qualities of Metals. 



441 



For other features the curves themselves as given in the paper may- 

 be looked to. 



Later experiments on the effects of pull transverse to the direction 

 of magnetization showed correspondingly opposite effects to those of 

 longitudinal pull, but with a " critical value " of magnetizing force 

 nearly twice as great. That for longitudinal pull, according to the 

 preceding figures, was about 23 times the Glasgow vertical force ; for 

 the transverse pull the critical value found was about 60 times the 

 Glasgow vertical force. The transverse pull was produced by water 

 pressure in the interior of a gun-barrel applied by a piston and lever 

 at one end. Thus a pressure of about 1,000 lbs. per square inch, 

 applied and removed at pleasure, gave effects on the magnetism in- 

 duced in the vertical gun-barrel by the vertical component of the 

 terrestrial magnetic force, and, again, by an electric current through 

 a coil of insulated copper wire round the gun-barrel. When the force 

 magnetizing the gun-barrel was anything less than about 60 times the 

 Glasgow vertical force, the magnetization was found to be less with 

 the pressure on than off. When the magnetizing force exceeded that 

 critical value, the magnetization was greater with the pressure on than 

 off. The residual (retained) magnetism was always less with the 

 pressure on than off (after ten or a dozen " ons " and " offs " of the 

 pressure to shake out as much of the magnetization as was so loosely 

 held as to be shaken out by this agitation). 



The vertical component of the terrestrial magnetic force at Glasgow 

 is about "43 c.-g.-s. units. Hence the critical values of the magnetiz- 

 ing force for longitudinal and transverse pull are approximately 10 and 

 25 c.-g.-s. units. With any magnetizing force between these limits 

 the effect of pull whether transverse or longitudinal must be to 

 diminish the magnetization. Hence it is to be inferred that equal pull 

 in all directions would diminish, and equal positive pressure in all 

 directions would increase, the magnetization under the influence of 

 force between these critical values, and through some range above and 

 below them ; and not improbably for all amounts, however large or 

 small, of the magnetizing force (?) ; but further experiment is necessary 

 to answer this question. 



The opposite effects of longitudinal and transverse pull, for magne- 

 tizing forces not between the critical range of from 10 to 25 c.-g.-s. 

 units, show an aeolotropic magnetic susceptibility in iron under aeolo- 

 tropic stress [that is, any stress other than pressure (whether positive 

 or negative) equal in all directions.] Consideration of the relation of 

 this result to Wiedemann's remarkable discovery of the induction of 

 longitudinal magnetization by twisting an iron wire through which 

 an electric current is maintained, is important and suggestive. In the 

 present paper a counter-influence is pointed out, in the aeolotropic 

 change of electric conductivity probably produced in the iron by 



VOL. XXVII. 2 G 



