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of the observations of planets and comparison-stars, we can from 
the years following only record a reduction carried out by Kaiser 
and published in Vol. 2 of the Annalen of the transit-observations 
made in September 1868 for the purpose of the longitude-deter- 
mination with Brussels In this paper Kaiser gave a number of 
important remarks on the reduction-elements of the meridiancirele, 
but at the same time he showed that the observations proved an 
anomalous behaviour of the collimation-constant, which could not be 
explained at the time. 
Some years later the first of us investigated for the Leiden 
meridiancircle the influence of an eccentric illumination of the field 
of the telescope, a question which was much discussed at the time 
and which, although very simple and although the true nature of 
the disturbance originating from it, when the adjustment of the 
ocular is incorrect, had been made clear by Carine half a century 
before, had raised a considerable amount of dust. With different 
positions of the ocular pointings were made on one of the 
meridian marks, using for the bisections the apparent position of the 
micrometer-thread outside the mark; for on the mark the central 
illumination by the mark itself exceeds the eccentric field-illumination 
and that part of the thread is always seen in its true position. 
From the variations of the readings for different positions of the 
ocular it was possible to deduce the position of the mirror in 
the cube of the telescope which reflected the light for the illumina- 
tion of the field and, on the instrument being dismounted in 1876, 
the actual position of the mirror was found to agree exactly with 
the calculation. In the alterations of our meridiancircle carried out 
by RepsoLp in 1876—77, amongst other things the field-illumination 
was modified and made exactly central. 
These results naturally suggested to E. F. B., that the disturbance 
of the collimation-constant occurring in September 1868 would find 
its explanation in the same phenomenon. The sign of the error 
arising from it, like the influence of a normal collimation-constant, 
must change on reversal of the instrument and one would have to 
suppose, that in the observations for the longitude-determination, 
especially those of the pole-star, (all transits were at that time 
observed by the eye-and-ear-method) the ocular had been pushed 
in too far. This did not appear improbable in itself, as the thread 
seemed if anything to become even a little finer, when the ocular 
was pushed in a little too far. 
It thus became the question, whether disturbances of that kind 
had to be suspected during the whole of the period 1864—68. In 
