314 



Thermodynamic Properties of Air. 



T. 



o 



+ 50 

 

 -10 

 -20 

 -30 

 -40 

 -50 

 -60 

 -70 

 -80 



The variation of resistance is about 2 ohms per degree ; 

 therefore it is easy to obtain a sensibility of ^° Cent. 



Experience has shown that the relation between resistance 

 and temperature undergoes slight changes when the thermo- 

 meter is employed at widely different temperatures. For 

 this reason it is better to avoid heating a thermometer destined 

 for low temperatures ; this might cause a variation of resist- 

 ance which would not disappear until after several months. 



E. 



T. 



K. 



1105-9 



o 



- 90 



801-8 



1000-0 



-100 



778-9 



978-5 



-110 



755-8 



956-9 



-120 



732-4 



935-2 



-130 



708-9 



913-4 



-140 



685-3 



891-4 



-150 



661*5 



869-3 



-160 



637-3 



847-0 



-170 



612-7 



824-5 



-180 



588-0 



Note added by the Author. 



It has been found since that fine iron wire answers the 

 purposes of low-temperature thermometry still better than 

 platinum. Both constancy and sensitiveness are greater. 

 The following data apply to an iron thermometer which has 

 been now four years in use. Diameter of wire = 0'035 millim., 

 resistance at 0° about 576 ohms. 



Displacement of Zero-point 



January 1892 

 March 1892 

 June 1892 



February 1893 

 December 1893 

 March 1894 



February 1896 



R =1001-80 ohms. 



1001-50 

 1001-23 

 1000-97 

 1001-10 

 1001-17 

 1001-12 



The sensitiveness is also nearly double that of platinum- 

 thermometers, as will be seen by the following table : — 



