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c) on the best means of utilising charts of gravity anomalies for
the determination of potential (always remembering that directly
observed values are preferable),
d) on the means of obtaining the most accurate and most convenient
values of orthometric heights.
4The I.A.G., in reviewing resolutions no. 6, no. 7, no. 8, adopted
at the IXth General Assembly in Brussels, taking note that valuable
research had been conducted as a result of these resolutionsconsider
ing that this research should be continued and developed, reaffirms
previous resolutions regarding
1) seasonal oscillations of the Earth's surface,
2) diurnal oscillations of the vertical and of the Earth's surface,
3) secular and sudden movements of the Earth's surface.
5. The I.A.G., considering that atmospheric refraction is capable
of causing serious systematic errors in levelling carried out along a
continuous slopethat these errors are related to the vertical gra
dients of temperature and perhaps to humidityexpresses the hope
that investigations be undertaken or continued in various countries
with the idea of correcting in a practical way, so far as is possible,
the levelling carried out along considerable slopes for the systematic
effects of atmospheric refraction.
6. The I.A.G., considering that any adjustment, even a provisional
one, of the European levelling networks will have scientific interest,
e.g. in the study of the vertical movements of the earth's crust, and
of the departure of mean sea-level from the geoidand that informa
tion about the junctions between the different European levelling
networks has now been nearly completely collected by Study Group
no. 5, and that the simple approximate method proposed by Dr. T. J.
Kukkamiiki gives satisfactory results on the basis of the material
available, has adopted the resolution' that the work of Study Group
no. 5, which has been working on the adjustment of the European
levelling networks should be completed in the following way
the collection of all available information about junctions between
different European levelling networks should be completed, and a
provisional adjustment should be made by the method proposed by
Dr. T. J. Kukkamaki to bring the datums of different countries all
into the same terms.
7. The I.A.G. reviewing the resolution no. 5 of the Brussels As
sembly, considering that interesting research has taken place in Egypt
regarding the statistical analysis of the results of levelling; consider
ing that a more thorough analysis of the distribution errors would
allo.w a better understanding of their physical natureconsidering
that a better evaluation could probably be found, resolves that a study
group be entrusted with the study of the most suitable means in
order to apply the mathematical statistics to the analysis of levelling
errors.
