30 



Experimental Researches on Drawn Steel. [Jan. 30, 



determined by the position of the point of intersection of the hot and 

 cold curves of magnetisation. 



Observations, extending over several years, then follow on four 

 magnets made of drawn steel and treated in two different ways so as 

 to have nearly zero coefficients, and the effects of time and the effects of 

 remagnetisation on the temperature coefficient and on the intensity 

 a,re studied. 



Part II. 



The series of wires representing the twelve stages in the manufacture 

 of drawn wire were subjected to examination for resistivity and its 

 temperature coefficient, for Young's modulus and its temperature 

 coefficient, and for density. 



Eesistivity is augmented by tempering but diminished by drawing 

 up to a certain stage ; extreme traction, however, causes a rapid 

 increase again of resistivity. 



The temperature coefficient is related to the resistivity, so that, in 

 general, high resistivity and low coefficient are associated. Drawing, 

 however, does not produce a very large change in the temperature 

 coefficient of resistivity. 



Young's modulus increases markedly with tempering and to a less 

 •extent with drawing up to the point where the resistivity is a 

 minimum ; after that, extreme drawing produces a sharp diminution 

 of the modulus. 



The temperature coefficient of Young's modulus presents an interest- 

 ing relation to the modulus and like the resistivity coefficient follows in 

 an inverse sense the modulus curve, so that when the modulus is large 

 the coefficient is small. 



It was observed that after heating and cooling the wire, the value of 

 Young's modulus did not return to its initial value but was always a 

 little greater ; perhaps this was not a permanent effect, although it 

 persisted for some time. 



A careful series of determinations on the density of the wires 

 showed that, with some initial irregularities, the density is very 

 decidedly increased by drawing to the very last stage, when it becomes 

 8 grammes per c.cm. 



There is a very close correspondence between density and magnetic 

 intensity, the two being nearly proportional to one another over a 

 considerable range ; there is also some evidence of agreement between 

 a smoothed curve of Young's modulus and the magnetic intensity; 

 both appear to be functions of the density. 



