Photography mi Aid to Astronomy. 
235 
For such a purpose photographic methods have not as yet proved 
available, and recourse was necessary to the older method of visual 
observing with the meridian circle. From observations made in the 
years 1897-1900 with the transit circle, an accurate catalogue of these 
8,560 stars has now been formed, and has been utilised for the purpose 
of standardising each of our plates. The heavy arithmetical work 
involved in applying to each of our original measures, over two 
millions in number, the derived correction to refer the whole to a 
common standard is now rapidly proceeding and at the present time 
is about half completed. 
I have above referred to the catalogue of 8,560 comparison stars 
as a framework for the support of the more extensive photographic 
catalogue. Such a framework, at least on the basis on which this- 
one was constructed, is not entirely self-supporting, and it thu& 
behoves us to carefully consider its foundations and to ensure that 
they possess the necessary solidarity. 
Not the least of the important questions brought up for discussion 
at the last meeting of the International Committee charged with the 
conduct of the photographic work, was that of the steps to be taken 
for this purpose. 
It was recognised on all sides that even the best existing meridian 
catalogues were inadequate, and that they would have to be supple- 
mented by extensive additional observations. The main object of the 
discussion was to secure the most extensive co-operation from obser- 
vatories provided with suitable meridian equipment, and to classify 
the work in various grades of accuracy, so that each establishment 
might devote itself primarily to that branch for which its equipment 
was best adapted, at the same time keeping in view the co-ordination 
of its work with the larger scheme. The resolutions adopted have 
since been favourably received by meridian observers, and we may look 
in the future to a systematic organisation of meridian astronomy 
throughout the world, the results of which, apart from the mere economic 
aspect, cannot fail to be of the highest importance to science. 
It may well be asked. What is the use of such a chart as you 
have been describing ? or, Will it repay the enormous cost involved in 
compiling it ? 
As regards its use, I endeavoured to indicate in my address last 
year some of the problems which awaited solution and which serve 
to inspire the astronomer in the conduct of the lengthy routine operations 
involved. These motives are perhaps for the most part intellectual 
rather than utilitarian, and it is possible, even probable, that to many 
of the questions arising answers which will afford complete satisfaction 
will not be forthcoming at least for a generation or two to come. 
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