30 



DR. F. HORTON ON THE EFFECTS OF CHANGES OF TEMPERATURE 



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Diagram IV. Showing the effect of temperature on the modulus of rigidity of platinum wire. 



The curve in this diagram bends in the opposite manner to that which was obtained 

 for soft iron. It is obvious that the rigidity of the wire falls off with increasing 

 temperature more rapidly than would be required by a linear law. The gradual 

 increase of rigidity with time which is greater the higher the temperature is, 

 however, continually acting in opposition to this, so that if it were possible to obtain 

 the rigidity of the wire at different temperatures, taking all the observations within 

 a very short space of time, the deviation from the linear law would be greater than 

 it is in Diagram IV. The shape of this curve for platinum is what one would expect 

 to obtain for a solid near its melting-point ; for as the melting-point is passed the 

 rigidity must become zero. (In the case of any solid with a latent heat it is not zero 

 at the melting-point.) It is difficult to understand why such a curve is given by 

 platinum one of the metals which, at ordinary temperatures, is furthest away from 

 its melting-point. 



The modulus of rigidity of platinum at 15 C. was found to be n l5 = 6'4GOO X 10 11 



