164 PROCEEDINGS OF SECTION A. 
That the rectilinear co-ordinates can and will be measured on 
the plates within the prescribed limit of 0-2”, there can be very 
little doubt ; but if we desire the greatest possible precision in the 
deduced stars places, our efforts must be directed to secure an 
equivalent precision in the cases of the stars taken as zero points ; 
and it seems necessary that whatever refinements may be devised 
and introduced, their adoption should be general and strictly 
uniform, for the influence of additional means and precautions for 
eliminating systematic errors from meridian observations and 
reductions would then be felt beneficially throughout the whole 
range of fundamental astronomy of position. 
It is appropiate to refer here to a proposal of Dr. Gill, made 
some three years ago, which bears upon this subjeet. 
Dr. Gill proposed that an International Congress of Astrono- 
mers be held, to answer, among others, the following questions, 
viz. :—“ Are astronomers prepared to enter upon a_ preliminary 
study, discussion, and experiment on the practical methods by 
which the art of observation may be raised to a higher level of 
accuracy, and its results be derived and published in a more 
systematic and homogeneous system ?” 
In recent years it has been sought to improve the determina- 
tions of star positions, by investigating certain minute errors 
which had previously either remained unsuspected, or considered 
too small for practical treatment. Among these may be classed 
the latitude variation, and the changes of personal equation in 
the same observer due to difference of star magnitude, declination, 
or reversed direction of the apparent motion of the star across the 
field of view. 
On the other hand, it has been questioned whether it would be 
advisable as yet to introduce the necessary corrections for these 
errors, owing to the disturbing elements and uncertainties by 
which their respective investigations may be affected, such, for 
instance, as the irregular and undetected variation of temperature 
of parts of the transit circles, the conditions of the observing 
room, and physiological questions. These matters have been and 
are being analy sed with extreme care by leading authorities in 
the astronomical world, but the results have not so far been 
finally accepted for general application. 
Further improvements in the reduction of meridian observa- 
tions have been looked for in another direction, namely, the 
revision and redetermination of astronomical constants. With a 
view (among other considerations) of deciding upon the adoption 
by the National Ephemeries of a uniform system of these con- 
stants, a Conference was held in Paris last year for the purpose 
by the Directors of the National Ephemeries and other prominent 
astronomers. 
