Astronomy. — “Qn a change with the declination in the personal 
equation in meridian-observations.”’ By C. H. Hins. (Com- 
municated by Prof. W. pe SITTER). 
(Communicated at the meeting of September 24, 1921). 
In the preliminary reduction of the R.A. in the current programme 
of the Leyden meridian circle, the question arose as how to deal 
witb the clock rate. 
The first difficulty that arises is that the registering clock KNoBLIcH 
is not the same as the principal clock of the observatory, Honwü 17. 
We shall therefore first give a brief account of how the reduction 
was made in former observations. 
Before the beginning and after the end of the observations the 
beats of Houwü 17 were registered for one and a half minute, with 
intervals of three seconds, on the slips upon which the KNOBLICH 
clock registers every two seconds. In this way the value of the 
difference of time Kn.—H. 17 was obtained at two epochs. Even 
when these comparisons were made three or more times in one 
evening, they were always represented by a straight line. (See 
PANNEKOEK, Annals of the Leyden Observatory Vol. X part U). 
At regular intervals of about ten days determinations of time were 
made which gave the daily rate of the clock Honwi 17. This 
“rough” rate observed in the interval between two determinations 
of time was reduced by the formula: 
p = daily rate —0s,0153 (6—760™™) + 0s,0263 (£°—10°) —0 ,37 (t—1’) 
to the so called reduced daily rate p at t=10°, b6=760™™ and 
t—t’ = 0. 
In the above formula 
b represents the mean barometer in the interval. 
t the mean temperature in the interval. 
t—t’ the mean difference of the temperatures at the top and the 
bottom in the case of the clock. 
daily rate: the rough rate as explained above. 
From this reduced daily rate the actual rate of H. 17 during the 
observations was derived by the above formula and the observed 
values of 6, t and ¢—t?'. 
All transits expressed in the time of the Kn. clock could be reduced 
to H. 17 time by means.of the interpolated difference Kn.—H. 17, 
or, which comes to the same thing, from the observed relative rate 
