A NEW CURRENT WEIGHER, ETC.' 



519 



avoid possible electromagnetic disturbances the oil was not stirred by a motor- 

 driven turbine, but by a stream of air forced through it. In a few of the earlier 

 determinations the standard cell was kept in the room containing the remainder of 

 the apparatus ; considerable variations in temperature were, however, experienced, 

 and as there was evidence of a slight lag in the E.M.F. of the cell it was removed to 



Fig. 24. General view of apparatus. 



a constant-temperature room in the basement. S', fig. 23, is a second standard cell 

 for the preliminary adjustment of the current, and the turning head T readily allows 

 of either cell being inserted in the potentiometer circuit. B is a battery of 55 accumu- 

 lators of 30 ampere hours' capacity; it is earthed at one point to eliminate electrostatic 

 effects (see p. 525). The resistance of the circuit can be adjusted by means of a set 

 of manganin coils and a mercury trough in N ; in all there are ten 10-ohm coils, 



