Thermometers Under the Shed
During the Observatory's Open Day in March every year, lots of visitors are attracted by the historical 1883 Building and take photos right in front of it. Meanwhile, a shed on the Observatory's lawn just next to the building also draws the visitors' attention. An official name for the shed is "Thermometer Shed". Thermometers respectively for measuring dry- and wet-bulb temperatures are placed under the shed.
The air temperature is directly measured from the dry-bulb thermometer while the relative humidity is calculated from the difference between temperatures measured by the dry- and wet-bulb thermometers. To obtain the actual temperatures, the thermometers are placed under a shed to avoid the measured temperatures being affected by direct sunlight and adverse weather conditions, and to allow good ventilation at the same time.
Thermometer shed is a special shelter used in tropical regions to house the thermometers. A thermometer shed has been used at the Observatory Headquarters in the late 1880s. The shed is covered by mattress and palm leaves which are required to be repaired or re-surfaced once every 5 years or so. Due to its bulky size, the Observatory has only installed a thermometer shed at its Headquarters. The conventional Stevenson Screen is used at the automatic weather stations over Hong Kong for housing thermometers.
Figure 1 Various meteorological instruments are installed at the Observatory's lawn.
Figure 2 Thermometer shed housing thermometers for measuring dry- and wet-bulb temperatures.
Figure 3 Stevenson Screen housing thermometers.