68 



Messrs. J. W. Swan and J. Rhodin. Absolute [May 24-, 

 FIG. 3. 



-8 metres 



The following is a description of the details : B was a single lead and 

 lead peroxide element, of a comparatively large capacity (30 ampere 

 hours). It was found necessary to have the capacity of the cell 

 tolerably large to avoid the necessity of making too large corrections 

 for the fall of potential in the cell itself between different observa- 

 tions. By means of a mercury contact key, K, the battery could be 

 short-circuited through a nickel wire resistance r (of about 6 ohms), 

 the standard ohm B and the resistance to be measured X. All these 

 resistances were in series. (The current in the main circuit was only 

 O2 or 0'25 ampere, and did not produce any sensible heating of the 

 ,various resistances.) By means of the current reverser, C (a mercury 

 switch), the current direction could be easily changed. The galva- 

 nometer, Gr, was connected with another mercury switch, Ci, by means 

 of which it could be put in shunt to the standard ohm and X alter- 

 nately in rapid succession. In the galvanometer circuit the resist- 

 ance box, BB, was inserted in order to render it possible to make the 

 deflections nearly equal when X differed considerably from R. 



