( 207 ) 
whereas, if we had neglected the consideration of the supplementary 
term, we should have found : 
1862—1867 M. E. = + 05,0382 
1868—1874 0377 
which values are considerably greater. 
IV. The period 1899—1902. 
17. Since the time, 1898 December, that the clock Honwi 17 
has been mounted in the niche of the pier of the 10-inch-refractor, 
its rates are kept under constant control by computations which are 
made, immediately after the time-determinations, by Mr. Hamersma, 
computer at the observatory. He computes moreover mean values 
of the rate at the end of every month, which are at once inserted 
in graphical representations. The following investigation was founded 
on these results only slightly modified. 
‘The modification is the consequence of a small correction of the 
barometer-readings caused by the fact that the temperature of the 
clock is no longer the same as that of the barometer in the transit- 
room. The barometer-readings were reduced therefore to what they 
would have been at the former temperature *). As my investigation, 
which includes no more than three years, must be considered as a 
preliminary one, it seemed useless to replace the original mean rea- 
dings by the mean values according to the barograph-diagrams. More- 
over the constant correction of the barometer used was neglected. 
As before the temperatures were determined from the readings of 
the upper one of the two thermometers suspended in the clock ease. 
The former thermometers had been replaced however by two other 
ones having centigrade scales. 
Besides the temperature in the niche below the eloekease has 
been determined for the period of a year by means of a thermo- 
graph of Ricnarp. It appeared that, even there, no trace of a daily 
period in the temperature is noticeable. 
In general the changes in the temperature have now become much 
slower and much more regular. At the same time the temperature 
in winter time does not nearly sink to so low a point as formerly ; 
this is shown even in the monthly means. In the years now under con- 
sideration the temperature in the clock case never sunk below + 2° C. 
_ As was done for the other periods, | have computed the differences 
1) The reduction amounted to 0.4 Mm, in maximo. 
i? 
