Si.)- David Gill. 
215 
with this sum the services of a competent photographic assistant was 
secured. Then he had the rare good fortune to open correspondence with 
Professor Kapteyn, of Groningen, who, with a fine unselfishness, offered to 
carry out all the necessary reductions for position and magnitude from the 
photographic plates. 
Kapteyn's letter to Gill will hear repetition : — • 
" I have talked the matter of the Photographic Durchmusterung 
over with Dr. Bakhuyzen and his brother. I am bound to confess that 
they were not very enthusiastic about the matter ; of course, they thought 
the results once reached of immense value, but the drudgery to be gone 
through before these results are once got into the form of a Catalogue 
almost unbearable. However, I think my enthusiasm for the matter 
will be equal to six or seven years of work." 
This was in December, 1885. In 1899 Kapteyn wrote :— 
" The Cape Photographic Durchmusterung may at last be considered 
complete. The w^ork has cost nearly double the time, the six or seven 
years, which I originally estimated would be required." 
We may fittingly say here that the carrying out of this magnifi- 
cent sidereal survey occupied from first to last fifteen years — years of 
unremitting labour, as the task meant the examination again, again, 
and yet again, of nearly half a million stars. 
Then there were times when difiiculties external to the actual work of 
reducing seemed to threaten the whole enterprise. It must have been 
vexatious to Gill to find that his own restricted proposals were in definite 
danger from his larger proposals for a comprehensive star map of the 
whole sky. 
It may be of interest to state what the difiiculties were. Work for the 
Cape Photometric Durchmusterung was begun on April 2, 1885, and so 
convinced was Gill of the value of this new method of recording the 
position and magnitude of stars, that he urged Admiral Mouchez to 
convene a congress of astronomers to consider how best to secure by 
photography a great catalogue of stars. It was evident that transit or 
meridian observations could never overtake a fraction of the work that 
photography could fulfil with ease. A single photograph might contain 
more stars than the most competent observer could measure and fix in 
a lifetime. 
It was in 1887 that this first International Astrophotographic Congress 
was held. To it tiiere came from all parts of the world no fewer than 
sixty leading astronomers. Gill was the guiding spirit of all the meetings, 
and before the Congress broke up it was agreed to begin at once a vast 
star map of the sky. Twenty observatories promised to co-operate in the 
undertaking, an undertaking which, when completed, will mean the cata- 
loguing of over ten million stars. 
