348 
the times of transit of each of the sun’s limbs are usually based 
on not more than three threads a closer investigation into this 
question would also have to be instituted beforehand. During this 
investigation a peculiar anomaly showed itself, the true nature of 
which was at first not recognized by us for a long time and, as a 
similar anomaly may also have occurred in other series of eye- 
and-ear-observations, it seemed to us of some importance to make 
a separate short communication on this point. 
2. Deduction of the thread intervals. Peculiar divergences 
in the observation of the transits. 
The reticule of the meridian-circle at that time contained 7 vertical 
threads. It is probable, that special ‘not very extensive series of 
observations were carried out each time to deduce the thread-intervals, 
as given in volume 1, although sometimes the method of deduction 
followed is not quit clear. The motives for the separation of the 
periods are not always equally clear either. Sometimes some per- 
turbation had taken place or the reticule had been cleaned, but 
in one case at least, that of the separation of the 6'" from the 5* 
period, the ground for it cannot be recognized in the least. 
However that may be, it seemed to us necessary to investigate 
the matter more closely by testing the intervals assumed each time 
on large numbers of transits of the fundamental stars observed, 
using the results of both observers and also, as much as possible, 
those obtained in both positions of the instrument designated in 
Leiden as clamp East and clamp West. In later years it had appeared 
at Leiden again and again, that small systematic differences may 
occur here dependent upon observer and position of the instrument. 
Using the times of transit reduced with the thread-intervals as 
assumed before, for each observation the differences middle thread — 
side thread were formed, which we shall call | A]. Further calling 
the corrections of the distances assumed for the threads I to VII (I is 
the one nearest the clamp) 4 I, All, etc, if there are no disturbances, 
we must have 
Thread Clamp West Clamp Kast 
I [Al= 4 Al [A] =—Al 
II i +All x see fl 
Ill : +Alil rm Sea HI 
Vv ke Pea AN 
VI ie ARNE 5 +A VI 
VII arches fal ATEN 
