PRESIDENT’S ADDRESS. 163 
to refer these images to the images of a number of stars within 
the same respective regions which shall have been fundamentally 
observed with our meridian circles, so that these may be used as 
zero points not affected by the uncertainty of proper motion. 
The Conference decided in 1896 that there should be ten such 
zero points in each plate if possible. 
We have, therefore, for the completion of the Australian part 
of the photographic catalogue, to form a catalogue of some 12,000 
or 13,000 stars, fundamentally observed with transit circles, and 
reduced to the epoch 1900. 
Owing to the great magnitude of these labours, the fear has 
been felt in some quarters that the refinement sought for the 
photographic catalogue is beyond our resources, and may indefi- 
nitely retard the termination of the work. This apprehension is 
not a fanciful one, and, as it arises from the practical view taken 
of existing circumstances, it is likely to produce discouragement. 
It may be that the intentions of the late Admiral Mouchez, the 
originator of the astrophotographic scheme, and the ideas enter- 
tained by the earlier Conferences, were not so ambitious ; but if 
we look further ahead, and consider from a broad point of view 
the purposes which the undertaking is intended to serve, there 
seems to be but one satisfactory conclusion, namely, that delay 
would be a lesser evil than want of refinement carried even to the 
utmost degree. 
The essential fact to be taken into account is, that this work 
is, to a very great extent, for the service of the next generation of 
astronomers, principally to enable them to solve more satisfactorily 
than we can at present the great problems of sidereal astronomy, 
which depend on the accuracy of a great number of relatively old 
observations of star places. 
Consequently it seems of paramount importance to attain in 
the astrophotographic catalogue the highest possible precision, 
even if it involved an excessive delay. 
It must be borne in mind that the probable error of star 
positions, as deduced from the photographic plates, cannot be of a 
smaller magnitude than that of positions determined by meridian 
observations. 
The accidental errors which evade analysis leave their element 
of doubt in observed star places, which will always remain with 
the photographic positions as well. The systematic errors, though 
capable of measurement and control to a great extent, are by no 
means governed by constant and perfectly known laws, and do 
not receive uniform treatment at the hands of all catalogue 
makers and computers. 
Some uncertainty is therefore involved also in the process of 
reduction, which will also affect all the photographic positions 
