( 405 ) 



This comparison teaches thai the four term formula for the represen- 

 tation of tlie observations may be considered to be almost equivalent 

 to the live term formula, and that therefore (this remark is in har- 

 mony' with note 2 of §13) for the calibration to — 217° the lowest 

 number of temperatures for which obserAations are required, amounts 

 to four. That three are not sufficient was already proved in § IJ. 

 This appears also clearly, when the mean error is determined, which 

 rises to ±7.6 microvolts for the three term formula. 



T A H L E IX. 



DEVIATIONS OF THE CALIBRATION-FORMULAE FOR THE 

 THERM 0-ELEMENT CONST ANTIN-STEEL. 



