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Thermometer Shed

Thermometer Shed

weather familyIn tropical regions, thermometer sheds were constructed to protect thermometers from radiation from the sun and sky, precipitation and any invasion of birds and animals.  They could also allow free circulation of air around the thermometers.

Thermometer sheds were first used in India in the last quarter of the nineteenth century.   They were called Madras huts or Bengal huts.  The construction varied from place to place and the thermometers were mounted in a cage suspended in the shed.

At the Hong Kong Observatory, an "Indian pattern"   thermometer shed was constructed in the late 1880s.  The shed had double palm-leaf roof with a 6-inch air space between the two roofs.  It covered 25 feet by 20 feet and was 3 feet high at the eaves and 9 feet at the ridgepole.  The shed was originally located 75 feet southeast of the main building and was relocated to 50 feet north-northeast of the main building in 1912.  In 1933, a new shed was reconstructed at the original site in the southeast corner of the compound.   This new shed was 20 feet by 15 feet with double palm-leaf roof extending to within 3 feet above the ground on all sides except the north, which was left completely open. Since then, although the shed has been rethatched or repaired many times, its location and construction remains practically the same.  Thermometers are mounted on a frame at the centre of the shed under the ridgepole with thermometer bulbs about 1.25 m above the ground.

A comparison of temperatures obtained between the shed and a rotating thermometer was made in 1935 and 1936, the differences were surprisingly low.  The then director came to the conclusion that in tropical climates temperatures measured by thermometers inside a well-exposed palm-leaf shelter would be more representative than those obtained inside a Stevenson screen.

Another comparison of temperature readings taken from the thermometer shed, from a Stevenson screen and from a rotating thermometer was carried out in 1978.   The conclusion was the same as before and the results were documented in the Hong Kong Observatory's Technical Note No. 49.