( 68 ) 
Astronomy. — #On the yearly periodicity of the rates of the 
Standard-cloch of the observatory at Leiden, Honwt Nr 17.4 
First part. By Dr. EB. F. van DE SANDE BAKHUYZEN. 
I. Zntroduction. 
1. When the observatory at Leiden was founded in 1861, it was 
fitted with a clock made by Mr. A. Honwié of Amsterdam, and by 
him designated as Nr 17. Accurate investigations of Kaiser *) soon 
showed the great regularity of its rate, in which point it was superior 
to all clocks about which an investigation had so far been published. 
Since that time it has continually been used as the standard-clock 
of the observatory and at the present moment its rate is still 
eminently satisfactory. 
The clock was originally mounted in the transit-room of the 
observatory on a brick pier which rests on the foundations of the 
meridian-circle. The stability of the mounting thus left nothing to be 
desired. On the other hand the temperature at this place was rather 
variable, showing very clearly a daily period; moreover entirely irre- 
cular changes of temperature were often caused by the opening and 
closing of the shutters. b 
From 1861 the clock has been going regularly until 1874, with- 
out being touched during this time except for the purpose of winding 
once a week. On the 17 of June of the latter year however it 
stopped spontaneously, after having shown for about a month a 
particular irregularity. 
As the intention existed already to make considerable changes as 
well in the transit-room as in the meridian-circle, it was thought 
best to defer a thorough cleaning and overhauling of the clock till 
the time of these alterations. Accordingly the clock was then only 
provisorily cleaned, and was set going again after a few days. 
The intended alterations were made in the second half of 1876 
and the beginning of 1877, and in June of that year everything 
was again in working order, and also the clock Honwi 17 was 
mounted again. 
Though Prof. H. G. van pr SANDE BAKHUYZEN did consider the 
possibility of removing it to a better position, out of the transit-room, 
1) F. Kaiser, Onderzoekingen omtrent den gang van het hoofduurwerk der 
sterrenwacht te Leiden, de pendule Honwi N°. 17. Versl. en Meded. K. Akad. 
Amsterdam D. X VII, 1865. 
F. Kaiser, Untersuchungen über den Gang der Hauptuhr der Sternwarte in 
Leiden, Honwii NY’. 17. Astr. Nachr. NO. 1502. 
