( 277 ) 
After the element has been set up in the way described, it is 
immersed in a thermostat, the temperature of which is maintained 
at 25° by means of a toluene regulator. By means of this 
regulator and a stirring arrangement (a small ships propeller kept 
in movement day and night by a Hernreici’s hot air motor) it 
was possible to keep the temperature at 25° during the whole 
period of the observations (about 6 weeks); the greatest variations, 
measured by means of a thermometer designed for thermochemical 
work, did not exceed 0°,004 C. The variations which occurred 
within 15 minutes could not, of course, appear in the element itself. 
It was, further, only of importance that the two limbs of the 
element should undergo the same changes of temperature. 
The standard cells, which were used in the measurements by 
means of POGGENDORFF’s compensation method, were placed in the 
same thermostat. 
The standard cells were: 
1. A Weston-cell made in April 1899. 
2. A CraRk-cell A , in January 1899. 
3. A CrARK-cell B  , in January 1899. 
A small accumulator ') was used as the working cell. 
Since all the measurements were reduced to the Westoncell, it 
appeared important to control it from time to time. This was done 
by means of the two CLARK-cells; as will be seen the E. M. F. of 
the Weston-cell remained absolutely constant during the whole 
period of the measurements. (See Table I). 
TABLE I. 
; E.M.F.Crark A 25° E.M.F. Crark B 25° 
Date Ratio — Ratio 
E. M. F. WesTonN 25° E.M.F. Weston 25° 
1 October 1.3946 1.3945 
10 October 1.3946 1.3945 
20 October 1.3946 4.3945 
27 October 1.3946 1.5945 
10 November 1.8946 1.3945 
20 November ?) 1.3946 1.8945 
1) These accumulators, having the very small dimensions 55 X 42 X 150 m.m. 
capacity 5,5 ampere hours, (weight when filled 880 gr.) are obtainable from the 
Berlin accumulator factory Andreas Str. 32, Berlin (O) at a cost of 3 Marks. They 
are to be strongly recommended for measurements of this kind. My friend Dr. Brepie 
of Leipzig drew my attention to these cells. 
2) The great reliability of the standards is further evident from the fact that in 
another test made on June 17, 1899 the same ratios 1.3946 and 1.3945 were obtained. 
20 
Proceedings Royal Acad. Amsterdam. Vol. IL 
