195 ) 
been continued afterwards, it finally appeared that, when the neces- 
sary corrections ') and the reduction for difference in altitude had 
been applied, the mean barometer-readings at both places are in 
perfect agreement *). | 
After the completion of this preparatory work H. G. vaN Dr SANDE 
BAKHUYZEN has been prevented by want of time from further inves- 
tigations of the rates of the clock Honwé 17. 
10. When last year the investigation of the clock in the period 
1862—74, was resumed by me, I have soon given up the attempt to 
derive trustworthy corrections for the barometer of Burrr and I too 
have used the readings at Utrecht. It appeared that in this way we 
can get a precision sufficient for our purpose, at least for the mean 
monthly barometer-readings. 
I had at my disposal readings of the barometer at Utrecht for 
205, 2% and 10". From these I derived mean barometerreadings 
reduced to 0° for the whole of our period *). In addition to these, 
however, we have readings of the barometer at Leyden for the last 
months. For, to begin with July 1873, the barometer in the transit- 
room has been regularly read five times a day. From these I could 
derive, in the same way as I had done for the time after 1877 mean 
barometerreadings, which afterwards I reduced to 0°. The comparison 
of the monthly means obtained in the two ways stands as follows 
L. — U. L. — U. 
1873 July + 0.3 Mm. 1873 Dee. + 0.8 Mm. 
Aug. 0.0 1874 Jan. — 0.2 
Sept. — 0.2 Febr. + 0.2 
Oct. — 0.2 March + 0.3 
Nov. — 01 April + 01 
The differences thus appear to be very small. They would have 
turned out still smaller perhaps, if we had not neglected the hundredth 
parts of the millimeters in all the computations. The mean value 
amounts only to + 0,05 Mm. 
1) About the errors of the barometer at Utrecht see: J. D. van per Praars, 
„Over den barometer van het K. Nederl. Meteor. Inst.” (Meteor. Jaarboek voor 1888). 
At Leyden the barometer-readings were reduced to those of the standard-barometer 
of Furss. 
2) See also: Annalen der Sternwarte in Leiden. Vol. VI pp. GXIV—CXVI. 
3) Ly taking the means of the readings at 10°, 205, 2%, 10° and giving half 
weight to both the extreme values I obtained the daily means from midnight to 
midnight. 
