232 



METEOROLOGICAL OBSERVATIONS. 



ture is 53°, and the daily range of temperature 13°. For 

 determining the temperature of the air an instrument known as 

 the thermometer is used. It consists of a closed glass tube with 

 a bulb at the bottom, which is filled with mercury. Heat causes 

 mercury to expand. The tube is graduated to correspond with 

 the temperature which is indicated by the height of the column 

 of mercury. 



The thermometers are hung in a hexagonal wooden shed, 7 

 feet in height, 3 feet 6 inches in width, and 2 feet 6 inches from 

 front to back, with conical roof. This shed stands on the flat 

 leaden roof of the Mu.seum and, above the level of 4 feet 2 inches, 

 is furnished all round with horizontal louvres 4 inches wide, 

 inclined outwards at an angle of 50 degrees and with interspaces 

 2^ inches wide, through which the air passes freely. The 

 underportion is pierced Jay numerous holes 1 inch in diameter. 

 All thermometers have Kew certificates. 



Maximum Temperature. This takes place during the 

 day and is registered by the maximum thermometer. This 

 instrument differs from the ordinary form of thermometer, by 

 having just above the bend near the bulb a small piece of glass 



H 



MAXIMUM TH:eRMOMETBR. 



which acts as a valve, allowing the mercury to pass upwards as 

 the temperature increases, but not permitting it to return when 

 the temperature gets lower. It therefore registers the maximum 

 temperature. The highest temperature registered at Truro was 

 92° on June 19th, 1893. 



MINIMUM THERM OMETE;r. 



Minimum Temperature. This takes place during the 

 night and is registered by the minimum thermometer. Instead 



