40 Dr. E. L. Nichols on the Electrical Resistance and 



In measuring the resistance of the hot wire, the galvanome- 

 ters were read simultaneously before and after each determi- 

 nation of the length. 



The following table gives the results of the measurements, 

 for temperatures ranging between 0° and a point not far below 

 the melting-point of platinum. Both resistance and length of 

 wire at 0° are taken equal to unity. 



Table I. 



Resistance. 



Length. 



Resistance. 



Length. 



l'OOOO .e. 



... 1-00000 



3-7090 ... 



.. 1-01229 



1-0410 ... 



... 1-00002 



3-7427 ... 



.. 1-01223 



1-5071 ... 



... 1-00125 



3-7813 ... 



.. 1-01285 



1-9000 ... 



... 1-00289 



3-8750 ... 



.. 1-01349 



2-1212 ... 



... 1-00380 



3-8904 ... 



.. 1-01371 



2-2934 ... 



... 1-00456 



3-9305 ... 



.. 1-01378 



2-3035 ... 



... 1-00489 



4-0303 ... 



.. 1-01450 



2-7821 ... 



... 1-00732 



4-0631 ... 



.. 1-01469 



2-8633 ... 



... 1-00763 



4-0655 ... 



.. 1-01495 



2-9696 ... 



... 1-00809 



4-0747 ... 



.. 1-01499 



3-3533 ... 



... 1-01022 



4-0841 .... 



.. 1-01514 



3-3741 ... 



... 1-01003 



4-1248 .... 



.. 1-01540 



3-4151 ... 



... 1-01042 



4-2005 ... 



.. 1-01567 



3-6449 ... 



... 1-01160 



4-2447 ... 



.. 1-01632 



III. Dr. Siemens has published three formulae for the 

 variation of the resistance of a platinum wire with the tempe- 

 rature. 



The temperatures were calculated in one case (formula a) 

 from the heating effect of a copper ball, the specific heat of 

 copper being regarded as a constant; while the other two for- 

 mulas were derived from measurements with the air-thermo- 

 meter. 



These formulas are: — 



r = -039369 T* + -00216407 T--24127, . . (a) 



r= -0021448 T* + -0024187 T + -30425, . . (b) 



r= -092183 T~* + -00007781 T + -50196, . . (c) 



where T is the absolute temperature and r the resistance of 

 the wire. The following formula by Benoit is also sometimes 

 used for the determination of high temperatures: 



r = 1 + -002445* + -000000572 1 2 (d) 



In this expression t denotes the temperature in degrees Centi- 

 grade. 



