( 194 ) 
Astronomy. — “On the yearly periodicity of the rates of the 
Standardclock of the observatory at Leyden, Honwü No. 17.” 
Second part. By Dr. E. F. van DE SANDE BAKHUYZEN. 
I. The period 1862—1874. 
9. As was mentioned, several investigations about the rate of the 
clock Houwt 17 during this period have been made by Kaiser. 
They have been partly published. These published investigations are 
relative to the period 1862 May—1864 August *). 
Afterwards, in the autumn of 1870, Kaiser undertook a new 
investigation founded on the period 1862—1870*). In 1872 this 
investigation was continued and extended over the last year and a 
half *). Kaiser was engaged in this investigation, the results of which 
were intended for the 3% Volume of the Annals of the observatory, 
till the last months of his life. It was unfinished, however, at his death. 
The results which Karser had obtained did not wholly satisfy him. 
Several singular irregularities had shown themselves; moreover he 
was aware of the fact that the barometer-readings, one of the foun- 
dations of the investigation, might still be affected by rather consider- 
able systematic errors, even after they had been corrected as well 
as possible. These barometer-readings had been derived by him from 
observations repeated three times every day on an old defective mer- 
cury barometer oi Burtr hanging in his study (during a year and a 
half on an Aneroid-barometer). The correction of this barometer 
was derived from simultaneous readings of the barometer in the 
transit-room. It appeared to be variable with the height of the 
barometer and increased considerably in the course of the years ; 
moreover the temperature of the barometer was quite uncertain. 
For these reasons H. G. VAN DE SANDE BAKHUYZEN, when in 1873 he 
planned the continuation of the investigation of the clock, deemed it 
necessary, first of all to procure better data about the atmospheric 
pressure to which the clock had been exposed *). He intended to derive 
these by the help of the regular barometer-readings made at the 
meteorological Institute at Utrecht. 
In the first place the constant differences between the barometer- 
readings at Utrecht and those at Leyden (the barometer in the transit- 
room) had to be derived. From extensive calculations, which have 
1) F. Kaiser |. c. 
2) Vide: Verslag van den staat der sterrenwacht te Leiden. 1870—71 pp. 15 and 16. 
3) Vide: Verslag van den staat der sterrenwacht te Leiden. 1871—72 pp. 14 and 15. 
4) Vide: Verslag van den staat der sterrenwacht te Leiden 1872—73 p. 4. 
