( 186 ) 

 of the several commutators may be considered ag perfectly certain. 



§ 5. The control of the thermo-elements. 

 It appeared : 



a. that when the four places of contact were packed in ice, the electro- 

 motive force of the element amounted to less than one microvolt; 



b. that the changing of the two places of contact constantin-steel, 

 so that they were alternately placed in the cryostat, indicated only a 

 very small difference in electromotive force. Care is taken, however, 

 that always the same limb is placed into the cryostat ; 



c. that while the place of contact was moved up and down in 

 the bath no difference could be perceived in the reading (hence 

 the difference of temperature certainly <^ 0^.02). 



All this proves that the electromoti\e forces which are raised 

 in the element outside the places of contact, are exceedingly small. 



§ 6. Corrections and calculations of the determinations of the 

 electromotive forces. 



a. In the following sections R^ Be R' have the meaning which has 

 been explained in Comm. N°. 89 § 3. E^-, Ec and E' signify the 

 electromotive forces of the observation-element, the comparison-element 

 and the Weston-battery respectively. If we have obtained 11,0 Re and 

 R' it follows that : 



Rw _ _ Rw 



Ew '== 



As a test we use : 



E,o = — Ec or E,, — — E'. 

 Rp R' 



E' 



En =^ Rr ' 



R' 



b. In order to find R^ we read on the stops of the resistance box 

 R'w (in the branch of small resistance),' and R'w (in the branch of 

 great resistance) which are switched in parallel to form /?^.. 



«. To none of the resistance boxes temperature corrections had 

 to be applied (nor to those given by Re and R' either). 



/?. To R'w we sometimes had to add the connecting resistance of 

 the stops. 



y. To Rw is added the correction to international ohms according 

 to the calibration table of the Phys. Techn. Reichsanstalt. 



Ö. To R'w is added the amount required to render the compen- 

 sation complete, which amount is derived from the deflections on 



