128 



Mr. Willoughhy Smith 



[June 6, 



however, it appears as if a very sluggish inductive effect were produced 

 in the diamagnetic metals of high conductivity, the sluggishness 

 increasing with the conductivity of the metal, as though the atoms 

 took a comparatively long time to accommodate themselves to the 

 changes in the magnetic field through which they were passing. 

 This, I think, confirms the theory I have ventured to advance with 

 respect to copper while under the influence of induction. 



If, as in the case of volta-electric induction, the lines of force are 

 generated too quickly; or, as in the case of magneto-electric induction, 

 the diamagnetic body passes too quickly through the magnetic field ; 

 the atoms of the substance, in each case, have not time to polarise with 

 sufficient rapidity to radiate in the same time or place as when 

 influenced more slowly by this force. This would account for the 

 apparent interruption of the lines of force by the copper plate in the 

 volta-electric experiments, and also for the " drag " or retardation on 

 the disc of the same metal, as shown by the blue colour in the diagram 

 whilst part of it is passing quickly through a magnetic field. That 

 being the case, it is easy to perceive that a speed of the copper disc 

 might be attained at which the current would be nil, through the 

 atoms being unable to polarise in the allotted time. Not so with 

 magnetic metals, as iron or nickel, in each of which the atoms appear 

 to be very susceptible to magnetic influences, and to polarise very 

 quickly, as shown by the way in which part of the disc is affected 

 just before entering the poles, as indicated by the blue colour in the 



diagram marked 3. 



Plate 3. 



The atoms must as quickly depolarise, as you perceive there is but 

 very little of what I have termed "drag " in those metals. The con- 

 sequence of this is, that with iron the amount of current is nearly in 

 direct i)roportion to the speed of the disc ; whereas with copper the 



