( 73 ) 
the two temperatures. There also seems to be a small yearly 
inequality. We will return later on to these small differences between 
the separate months, and investigate the influence which they can 
have had on the rate of the clock, ¢f they are real. 
For the rest of the investigation the readings of the upper thermo- 
meter were used exclusively. I first formed daily means‘) — the 
day being reckoned from midnight to midnight — and then means 
for the periods of about one month. The index-correction, which may 
be taken constant and equal to — 0°.6 for the whole period, was 
not applied. 
Until May 1886 the heights of the barometer were read and 
reduced in exactly the same way as the temperatures. The readings 
were made on a mercurial barometer which was suspended in the 
transit-room from the same pier which also carried the clock. After 
that time a barograph of Richard was used, which was placed on 
the top of this same pier. Its corrections were determined by 
comparison with the mercurial barometer ®). The daily means were 
then derived by integration by means of a planimeter of AMSLER. 
During the period in question three different cistern barometers 
were used; in consequence of cleaning and refilling we must however 
distinguish 7 periods. The corrections for these 7 periods were 
determined by intercomparisons, by comparisons with simultaneous 
readings of the barometer of the Meteorological Institute at Utrecht, 
and finally by comparisons with a #Cistern-syphon” barometer by 
Furss, which in 1890 was provided for the observatory, to be used 
as a Standard barometer. Since however before 1890 no correction 
had been applied and the neglected corrections amounted to approxi- 
mately + 0.3 mm. during the whole period, the readings after 1890 
were reduced to: Normal barometer — 0.3 mm. 
The barometer-readings were not reduced to 0°. This reduction 
was omitted on purpose, though the errors introduced thereby are 
by no means negligible (at 7608" the effect of 1° Raum. is 0.15 ™"). 
The influence of these errors on the rate of the clock is however 
nearly completely compensated by the fact that also the influence 
of the temperature on the rate, which is thus found, differs from the 
true one. It is here supposed that the temperatures of the barometer 
has always been equal to that of the pendulum, which condition is 
1) The mean was taken of the readings at 12, 205, 40, 12, giving half weight 
to the extreme values. 
2) A constant correction was taken for each weekly barograph sheet derived 
from one or two readings of the mercurial barometer daily. 
