.S/A- \\-ll.LlA.\I .S7A.J//-.V.S-, l-.R.S. 



439 



IAI5LK IV. 



\VIKI-: TMK SAME AH IN III. 

 CURRENT DECI: I:\-IM.. 



The results given in the four tables are plotted out on the curve 

 marked (A) (Plate 36). The abscissae give the rate at which the 

 energy of the current is converted into heat, and the ordinates 

 the corresponding resistance of the wire. 



To determine the temperature of the wire corresponding to each 

 resistance, another series of experiments was made, which are 

 described hereafter. The values of a, /3, and y obtained were 



a = 0-0119 j 

 /3 = 0-00112 I 



7 = 0-512 ) 



y 

 hence ' = -0119T+ -00112T + -512 ; where r is the resistance 



r o 

 of the wire at the freezing point. By giving to T various values 



in this formula, a curve can be constructed showing the relation 

 between the resistance and absolute temperature. Such a curve 

 was drawn, and approximated for high temperatures to a straight 

 line, as evidently must be the case from the form of the equation. 



By solving the equation for the maximum value of observed, it 



r o 

 was found that the temperature of the wire when bright red hot 



was about 1100 C. It is known that platinum wire melts at 

 approximately 1800 C. 



