( 185 ) 



juncture are in contact with each other, but we only require that 

 a definite ele;ctromotive force for a definite temperature of the bath 

 in which the element is immersed should be accurately indicated, 

 (for the rest comp. § 5). 



In order to lessen the influence of the conduction of heat along 

 the wire at the juncture we shall for the new elements destined for 

 taking the temperature of a liquid bath make a trial with the insertion 

 into the glass tube at 2 cm. above the copper rim of the copper 

 block of a copper tube, 5 cm. long, which is soldered on either 

 side of the glass tube and remains over its whole length immersed 

 in the liquid. 



§ 4. Precautions at the measureme?its of the electromotive forces. 



a. The apparatus and connections which have been described in 

 § 3 of Comm. K". 89 have been mounted entirely on paraffin, with 

 w^hich also the enveloping portions of the apparatus are insulated. 

 Only the wares running between the different rooms stretched on 

 porcelain insulators, of which the high insulation-resistance has 

 repeatedly been tested, have no paraffin-insulation. The ice-pots are 

 hanging on porcelain insulators. As a matter of coui'se, all parts of 

 the installation have been carefully examined as to their insulation 

 before they are used. 



h. The necessity of continually packing together the ice in the 

 ice-pots has been argued before in Comm. N°. 89. 



c. The plug-commutators are of copper. All contacts between different 

 metals in the connection have been carefully protected from variations 

 of temperature by packing of wool or cotton-wool, from which they 

 are insulated by paraffin in card-board boxes. This was only omitted 

 at the contact places of the copper leads with the brass clips of the 

 resistance boxes. To secure to the Weston-elements an invariable 

 temperature, the latter have also been carefully packed. The accu- 

 mulator is placed in a wooden box. 



d. With regard to the testing elements, care has been taken that 

 the steam left the boiling apparatus (comp. Comm. N°. 27, § 8) at 

 a given constant rate. 



e. Before a measurement is started we investigate by short-cir- 

 cuiting in the copper commutators in the conductions, leading from 

 the thermo-elements and the Weston-battery to the connections, whether 

 all electromotive forces in the connections are so small and constant 

 (not more than some microvolts), that elimination through the re^•ersal 



