METEOROLOGICAL OBSERVATIONS, 



235 



measured. Another instrument often used is that known as the 

 Campbell-Stokes Eecorder * The rays of the sun are received on 

 a sphere of glass, 4-ins. in diameter, and concentrated on a card 

 placed in a groove at the back, the surface of which becomes 

 charred, and so gives a record of the duration of bright sunshine. 



The month during which most sunshine is recorded in Truro 

 is May, the average being 253-8 hours. December is the least 

 sunniest, the average being only 49-1 hours. The greatest 

 duration of sunshine in one month was 320 hours registered 

 during the month of May, 1896. The year of greatest sunshine 

 was 1899, with 1893-8 hours. 



Rainfall (diagram 4). It is important that the amount of 

 rain falling at di:fferent places should be ascertained. The 

 instrument used for collecting the rain is called the Eain Guage. 

 It consists of a metal funnel, usually five inches in diameter, 

 placed over a metal cylinder which contains a glass receiving 

 vessel into which the neck of the funnel is inserted. The 



N^^INCHl 



RAIN GUAGK. 



measurement is effected by pouring the contents into a measure 

 graduated to represent tenths and hundredths of an inch, and 

 reading off the division to which the water rises. One inch of 

 rain on a square yard gives 4-67 gallons, or 47-74 pounds ; on an 

 acre it corresponds to 22,662 gallons or 100-99 tons. December 

 is the wettest month in the year, the mean rainfall for that 

 month in Truro being 4-835 inches. The highest rainfall for 



* In use at the Falmouth Observatory. 



