347 
that case the computation of the absolute azimuth especially would 
become much more difficult and the importance of the observations 
for the determination of absolute Right-Ascensions might perhaps 
be materially reduced. Fortunately a few years later in 1882, when 
the first of us at the request of Newcoms undertook a revised reduc- 
tion of the Leiden observations of Mercury, which naturally involved 
some investigations, albeit provisional ones, on the instrumental con- 
stants, it was found that during the whole period of the Fundamental 
Observations 1864—July 1868 somewhat considerable influences of 
the eccentric illumination could not be detected, 
The old series of fundamental R. A. observations thus continued 
fully to deserve an accurate systematically planned reduction and 
discussion, but the great extent of the work was gradually giving 
rise to the fear that it would bardly be undertaken any more, when 
last year the second of us resolved to undertake the task, at least 
for an important part, notwithstanding the considerable difficulties 
arising from the present circumstances which compel him to reside 
outside Leiden. 
The working plan to be followed was then agreed upon by us. 
The main object would be, assuming the relative R. A. of the fun- 
damental stars as given by Auwers’s New Fund. Cat. or by that of 
Newcoms, to deduce from the observations of the sun a new deter- 
mination of the Equinox for 1865. The declination-observations of 
the sun, as recalled above, had already been discussed by the first 
of us a long time ago, and consequently by this procedure data 
would be obtained regarding the advantages and disadvantages 
of the method of separate treatment of the two coordinates of 
the sun. 
The work proper would be preceded by a new and rigid inves- 
tigation of all the reduction-elements and ‘all errors and peculiarities 
of the instrument and the observers, for which purpose the inves- 
tigations formerly instituted at Leiden could serve as a first approxi- 
mation, and the results of two special investigations regarding the 
value of the divisions of the level used and the irregularities of 
the pivots could immediately be utilized. 
In the first volume of the Annalen the means of the times of 
transit reduced to the middle thread are given for all the observations, 
while in the introduction on page LXXXVIII are mentioned the 
values of the thread intervals which were used in the reduction, 
the total period having been divided into six parts, for which different 
values were assumed. It soon appeared to us, however, that in 
view of the degree of accuracy now aimed at, and the fact that 
