506 



Elongation produced in Soft Iron by Magnetism. 



Diameter, 

 in milliin. 



Length, 

 in millim. 



Ratio of 

 D to L. 



Elongation in 

 fraction 

 of length. 



Observer. 



Magnetic 

 field. 



127 

 9-5 



7-9 

 3-15 

 19-5 



15265 

 9144 

 700-0 

 1000 



52 



•0083 

 •0104 

 •0113 

 ■0315 

 •3750 



•0000019 

 •0000028 

 •0000038 

 •0000042 

 •00001084- 



Mayer. 

 Joule. 

 Lochner. 

 Bid well. 

 Berget. 



60 



59 



540+ 



635 



\ 6-35 



635 



7000 

 435-0 

 1950 



•0090 

 •0146 

 •0326 



•0000031 

 •0000042 

 •0000045 



Lochner. 

 Lochner. 

 Lochner. 



56 



66 



119 



Bars I., II., III., and VI. were all of the same length ; their 

 respective weights were 350, 192, 160, and 217 grams. 



The following table seems to indicate that the expansion 

 varies with the magnetic moment per unit volume or mass as 

 well as with the form of the bar. 



Bar. 



Moment 

 per grm. 

 Field 200. 



Batio 

 D:L. 



A 



Fringes, 

 Maximum 

 Expansion. 



I. ... 



175-3 



•0136 



•117 



10-3 



II. ... 



1531 



•0101 



•100 



5-6 



III. ... 



173-6 



•0091 



•095 



7-4 



VI. ... 



170-6 



•0107 



•107 



7-2 



It may be stated briefly that my observations furnish the 

 following evidence in regard to the expansion which takes 

 place in soft iron bars : — 



1st. They confirm the general form of Mr. Shelford Bidwell's 

 curves. 



2nd. They indicate that the expansion is a function of the 

 ratio between the diameter and length, and that the elongation 

 varies directly as possibly the square root of this ratio. 



3rd. They further indicate that the expansion varies directly 

 as the permeability. 



4th. That the amount of current required to produce the 

 maximum expansion, and also the point of no expansion, 



