CO129-516-8 Survey of Hong Kong 24-4-1929 - 11-11-1929 — Page 25

Copy.

Enclosure No. 5.

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The Longitude of the Royal Observatory now in use is

7h.36m. 41.25s.E. It was determined by 13 observations of the

Bordeaux radio time signal made simultaneously at the Royal

Observatory, Greenwich and the Royal Observatory, Hong Kong in

September/November 1924, and has been adopted for use since January 1st 1926. No correction was made for the time of

transmission of the radio signal, but it is thought that any

correction to be applied later (on this account, or to bring the

longitude into agreement with the lnternational determination

of Longitudes by wireless telegraphy) will not exceed 0.05s.

Details of the original determination of the longitude

of Hong Kong are to be found in "Telegraphic Determinations of

Longitude in the East Indies, China and Japan 1881-1882′′ in No.

65b of the Hydrographic Office U.S. Navy 1883.

Briefly, Commander Green determined the difference of

Longitude between Madras and Hong Kong as 2h.15m.39.43s., and

the difference of longitude Hong Kong-Vladivostock as lh.10m.52.

07s.

In the absence of any record, it is assumed that the

longitude of the Royal Observatory was calculated as below. It

should be noted that Commander Green's observing station was

Palos pier on the site of the Naval Yard.

h m S

h m s

-1.10.52.07

Longitude Madras 5.20. 59.43E Long Vladivostock 8.47.31.31£ Madras-Palos Pier 2.15. 39.43 VL.-Palos Pier Long.Palos Pier 7.36. 38.85E Long.Palos Pier

h m $

Mean 7.36.39.045E.

Diff. Long.Palos Pier and

Meridian of the Transit

Instrument, Royal Observatory)

7.36.39.245

Hong Kong 3966 feet

Long. Royal Observatory

2.815.

7.36.41.86 E.

determined by triangulation by Public works Department.

The