650 ‘ 
For this purpose it was interesting to investigate whether the devia- 
tions of the effective area from the real area presented the same 
course for different pressure balances. We might obtain some idea 
of this by comparing the pressure balance of Prof. Conrn at Utrecht 
with the small and the large pressure balance belonging to the 
apparatus of the vaN DER Waats fund, which comparison took place 
at Amsterdam from October to December 1915. 
Investigation. The Utrecht pressure balance looks entirely the 
same as the small Amsterdam one; only the real area is not 1, 
but + em*… so that its range of measurements reaches to 1000 
atmospheres. The comparison of the effective area of the two appa- 
ratus was carried out by using a measuring tube filled with hydrogen, 
as it has been described by Warsrra in his Thesis for the Doctorate’), 
as indicator. Then the measuring tube was successively brought in 
connection with the two pressure balances that were to be compared, 
the temperature of the gas being kept constant as well as possible 
at 25°. The results of the measurements at different pressures for 
different fillings in different measuring tubes on the given data are 
recorded in the following two tables. 
TAS CE 
Ratio effective area Amst. small and Utrecht press. bal. 
ect co A RE RAI a IT 
88 3.993 
109 3.993 3.993 
147 3.993 
151 3.993 | 3.992 | 3.993 3.992 
167 3.991 
195 3.993 | 3.991 | 3.991 
204 3.991 
223 | 3.992 
242 3.990 | 3.991 | 3.991 | 3.991 | 3.990 
K. W W. Watstra, Dissertatie Amsterdam 1914. Cf. These Proc. Vol. 16, (1913) 
D4 a 
ij 
754 and 822, Vol. 17, (1914) p. 208. 
p. 
