.
644
(
Draft Note.
It apparently has not been realised in Hong Kong that
the methods of measuring humidity have been frequently
investigated by physecoats of first class repute both in
Europe and America. The results of their work have from time
to time been discussed by international meteorological
congresses; and an authoritative summary of the conclusions
reached was included in the "Internationaler Meteorologischer
Koder' published in 1907. A second edition was brought out
in 1911 by the Prussian Meteorological Institute (Berlin 1911)
and extracts have been given as an appendix. For the
measurement of air temperature and humidity, although no
binding rule is laid down, it is recommended that for first
class observatories the Assmann Aspiration- thermometer and
the Assmann Aspiration psychrometer should be adopted as
the standard instruments and that whatever methods of
measurement may be adopted, they should be compared from time
to time with the readings of these instruments.
2. Sling thermometers have been used for many years in the
United States, where the observers are far more capable men
than are to be found in ordinary tropical observatories; hence it may be assumed that the international committee has been familiar with them and has deliberately passed them over in accepting Assmann's methods as superior. I may add that a comparison between the temperature results obtained in our Indian standard sheds and those given by the Assmann instrument has been in progress for upwards of a year at Agra and shows
a satisfactory agreement; the work has been interrupted by the war and the results cannot be published for some time.
3.
Tuming to the Directos report of 14th April 1918 I have not seen His Excellency the Governor of Hong Kong'e despatch of 14th January 1918 and do not know the jutification for the statement that the Hong Kong practice is 'known to be more accurate than the Indian method'. The principle on which our reduction tables are based are stated on pages Viii and ix
of
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