192 Prof. A. M. Mayer on the Magnetic Elongations 



elongation is yet *65 of a division, whereas when the circuit is 

 at once formed with this same interposed resistance the rod was 

 elongated only '05 of a division. 



The discovery of this most remarkable phenomenon was con- 

 tained in the above experiments ; but to be sure that my expe- 

 riments should not mislead me I repeated them several times, 

 using every precaution to ensure their accuracy, and obtained 

 results almost identical with those formerly observed. I am 

 therefore confident that I have discovered a phenomenon worthy 

 of minute study ; and I purpose to make it the subject of a spe- 

 cial investigation. 



Unfortunately, during the above experiments I did not make 

 a parallel series of determinations of the magnetic intensities of 

 the rod during the successive stages of passing a current of in- 

 creasing and of decreasing strength. Yet I can hardly believe 

 that the magnetic intensity will be kept up with the persistent 

 elongation of the rod when it is slowly demagnetized; I 

 think it will be found that the magnetic intensity of the rod 

 depends alone on the strength of the current traversing the 

 helix. The phenomenon indeed shows that, the molecules of 

 the rod on its elongation by magnetization having been forced 

 into new positions, the molecules, either by what might be 

 well called a "magnetic set"* or from molecular friction, re- 

 tain these new positions with such persistence that it requires 

 the sudden shock of the induced current produced on breaking 

 the circuit, to cause them to rush to their positions of stable 

 equilibrium. 



Effects observed on making and breaking separate currents in the 

 two component helices of the compound helix. 



In these experiments two batteries were used. In the outer 

 helix I made and broke a current from sixteen cells, arranged 

 four coupled and four in series. In connexion with the inner 

 helix I used a battery of 25 cells, connected five in a row and 

 five in series. The experiments are interesting, as showing the 

 effects of the induced currents formed on making and breaking 

 the circuits in the various manners given in the following : — 

 (1) Made circuit in inner helix ; rod elongated 1*4 division. 

 „ „ outer „ „ -25 „ 



Broke „ „ „ retracted *25 „ 



„ inner „ „ 1-4 „ 



* The term " magnetic set," as applied above, is, by analogy, an appro- 

 priate name for the phenomenon ; but it cannot well be so applied, because 

 Dr. Joule has already appropriated " magnetic set " as designating the re- 

 sidual magnetism an iron rod retains after its electromagnetization. 



