5.4 Collaborating with David Gill
75
scale of the Solar System. In 1879 he was appointed ‘Her Majesty’s Astronomer’
at the Royal Observatory at the Cape of Good Hope, where he would remain
until his retirement in 1906.
It has been suggested, in the biography of Kapteyn’s daughter as well as
obituaries and other biographical articles about Kapteyn, that the collaboration between Kapteyn and Gill arose when Kapteyn read an article during the
Christmas holidays of December 1885, in Leiden, in which Gill described his
plans to construct a star catalog of the southern sky using photographic exposures, and sought help with this. Kapteyn would have spontaneously offered
his services. But that is not at all how it happened. Such an article by David Gill
does not even exist; it would have been published in the British journal the Observatory, but there is no such an article in it. What happened is the following.
Kapteyn himself sent his article on the measurement of absolute declinations
and polar height to Gill with an accompanying letter dated April 30, 1884. In
it he refers to an article that does exist, by David Gill in the Vierteljahresschrift
of the Astronomische Gesellschaft on the question of absolute declinations.
Gill wrote back (with some delay) that he found the article ‘a model of clarity’.
He also suggested setting up an observing program to put Kapteyn’s ideas into
practice.
Interestingly, David Gill wrote some time later that he had Kapteyn’s article translated from German into English because he was not very good at
languages; he added that ‘it is all clear to me now’ (!!). The annual reports
of the Cape Observatory do mention observations for the Kapteyn project
for several years, but as far as I know no final results were ever published. In
1882 Gill had made photographs of the ‘large comet’ that was visible that
year, and he had noticed that there were large numbers of stars visible on the
plate (Fig. 5.5). Now above we saw how the Bonner Durchmusterung had been
produced in the northern hemisphere, which had yielded relatively accurate
positions and brightnesses of stars up to at least magnitude 9–10. This had
then been extended from Bonn to all stars that were visible from there in the
Südliche Durchmusterung, but most of the southern sky had not been mapped
to any reasonable accuracy for all but the brightest stars. It was planned to
do this from the Córdoba Observatorio Astronómico in Argentina, but it had
not gotten very far yet. And the intention was that, like the northern duchmusterungs, it would be done star by star with a meridian circle, which could
take many years. David Gill realized that in principle it could be done much
faster with photographic images. He therefore started taking the first exposures with a specially built telescope with a lens of 15 cm and a focal length of
137 cm (see Fig. 5.6). But he had absolutely not the time nor the manpower
to measure up those plates.
75
scale of the Solar System. In 1879 he was appointed ‘Her Majesty’s Astronomer’
at the Royal Observatory at the Cape of Good Hope, where he would remain
until his retirement in 1906.
It has been suggested, in the biography of Kapteyn’s daughter as well as
obituaries and other biographical articles about Kapteyn, that the collaboration between Kapteyn and Gill arose when Kapteyn read an article during the
Christmas holidays of December 1885, in Leiden, in which Gill described his
plans to construct a star catalog of the southern sky using photographic exposures, and sought help with this. Kapteyn would have spontaneously offered
his services. But that is not at all how it happened. Such an article by David Gill
does not even exist; it would have been published in the British journal the Observatory, but there is no such an article in it. What happened is the following.
Kapteyn himself sent his article on the measurement of absolute declinations
and polar height to Gill with an accompanying letter dated April 30, 1884. In
it he refers to an article that does exist, by David Gill in the Vierteljahresschrift
of the Astronomische Gesellschaft on the question of absolute declinations.
Gill wrote back (with some delay) that he found the article ‘a model of clarity’.
He also suggested setting up an observing program to put Kapteyn’s ideas into
practice.
Interestingly, David Gill wrote some time later that he had Kapteyn’s article translated from German into English because he was not very good at
languages; he added that ‘it is all clear to me now’ (!!). The annual reports
of the Cape Observatory do mention observations for the Kapteyn project
for several years, but as far as I know no final results were ever published. In
1882 Gill had made photographs of the ‘large comet’ that was visible that
year, and he had noticed that there were large numbers of stars visible on the
plate (Fig. 5.5). Now above we saw how the Bonner Durchmusterung had been
produced in the northern hemisphere, which had yielded relatively accurate
positions and brightnesses of stars up to at least magnitude 9–10. This had
then been extended from Bonn to all stars that were visible from there in the
Südliche Durchmusterung, but most of the southern sky had not been mapped
to any reasonable accuracy for all but the brightest stars. It was planned to
do this from the Córdoba Observatorio Astronómico in Argentina, but it had
not gotten very far yet. And the intention was that, like the northern duchmusterungs, it would be done star by star with a meridian circle, which could
take many years. David Gill realized that in principle it could be done much
faster with photographic images. He therefore started taking the first exposures with a specially built telescope with a lens of 15 cm and a focal length of
137 cm (see Fig. 5.6). But he had absolutely not the time nor the manpower
to measure up those plates.