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25 
Astronomy. — Preliminary investigation of the rate of the standard 
clock of the observatory al Leyden Honwt N°. 17 after it 
was mounted im the niche of the great pier.’ By Dr. E. F. 
VAN DE SANDE BAKHUYZEN. 
1. In a preceding paper on the clock Honwé 17 I communicated 
the investigations I had made on an inequality of a yearly period 
noted in its rate which does not depend on the actual temperature. 
Besides the periods 1861—1874 and 1877—1898 I discussed also 
the period 1899—1902 when the clock had been mounted in the 
hall of the observatory in a niche cut out for this purpose from the 
great pier. From the mean daily rates during periods of about a 
month each, I derived formulae for the rate in two different ways, 
and this research clearly brought to light that during this period the 
rate of the clock had become considerably more regular than before 
and now satisfies high demands. 
Since that time the same formulae have been compared with the 
daily rates observed during much shorter periods and an investigation 
has been undertaken about the barometer coefficient, for which purpose 
the monthly rates were less appropriate. 
The latter calculations have so clearly shown the excellence of the 
‘clock also with regard to its rate during periods of a few days, that 
it seemed to be of interest briefly to give here the results to which 
they led. 
2. The results we obtained from the previous investigations may 
be resumed thus. | 
Under all the conditions in which the clock Honwt 17 has been 
placed, its rate, after correction for the influence of the temperature, 
has always shown a residual yearly inequality. As the former influence 
had been derived from the yearly variation of the temperature, the 
residual inequality must necessarily show a difference of phase of 
three months with respect to the temperature. 
If the influence of the temperature had been derived and accoun- 
ted for in the form = c, (#—t,) + c, (t—t,)", whether we had found 
for c, a small negligible value, as in the period 1862—1874 or an 
obviously real quantity as in the period 1899—1902,, the residual 
inequality could with sufficient accuracy be expressed by a simple 
sinusoid. If on the contrary only a linear influence of the temperature 
had been accounted for, while an investigation of ¢, showed it to 
have an appreciable value, the residual inequality showed a half- 
yearly term besides. This could be expected; for as long as only the 
Re) 
Proceedings Royal Acad. Amsterdam, Vol. \ 
