zipon the Dimensions of Iron and Steel Bars. 229 



Experiment 10. Pressure i80 lbs. 



The numbers in the last columns of the preceding tables 

 show that the elongation follows a rather higher ratio than 

 the square of the magnetic polarity. In the former section, 

 in which all the bars employed were a yard long, the ratio was 

 somewhat lower than that of the square of the polarity in the 

 case of well-annealed iron. I am inclined therefore to think 

 that the anomalies referred to at p. 83, were occasioned rather 

 by the too great length of the iron bars, which prevented 

 them from being magnetized as much at the ends as at the 

 middle })art, than by their different magnetic conditions at the 

 centre and surface. 



From the above tables it appears evident that the augmen- 

 tation oi pressure does not make much difference in the amount 

 of elongation for the same quantity of polarity. However, I 

 thought it desirable to try the effect of a greater pressure. 

 For this purpose I employed a piece of soft iron wire, six 

 inches long and one-fourth of an inch in diameter. This iron 

 pillar stood upon a small piece of flattened brass, resting iipon 

 a block of hard wood six inches high, in order that it might 

 be sufficiently elevated to support the lever. It was placed in 

 the axis of a suitable coil, 5,} inches long and one inch in in- 

 terior diameter, constructed of a covered copper wire twenty 

 yards long and one-tenth of an inch in diameter. 



