117 
In the measurements the current varied from 10 to 40 amp. and 
was obtained from three 60 volt batteries of accumulators, coupled 
in parallel. 
For the absolute determination of Verrpert’s constant the current 
was measured with an ammeter having three ranges (O—2, O0—20, 
O—50 amp). This ammeter was calibrated on the potentiometer, 
and, moreover, when taking the photographs, the variation of the 
current was so chosen that the pointer of the instrnment coincided 
with the graduations as during the calibration, so that the current 
is known with certainty to one-tenth of an amp. (one scale division 
= 0,5 amp.) 
The pressure was measured on a ScHAFFER and BUDENBERG metal 
manometer with a circular scale of 16 em diameter, reading up to 
150 kg/em? by steps of '/, kg/em*. The greatest difference between 
two independent calibrations did not exceed 0,1 kg/em*. We assumed 
therefore that the pressure is accurate to 0,1 ke/em*. 
The manometer was coupled directly to the experimental tube, 
and, along with it, could be shut off from the rest of the appara- 
tus by means of a tap. The rest of the apparatus consisted of 
a gaseylinder and an airpump (a GaArpr vacuum kapsel-pump) ; 
AN p . 
Fig. 2. 
there was also an exit tap for the gas in the experimental tube, as 
it would not have been good for the nicols to expose them to 
the high pressure for days on end. 
