Dr G. C. Simpson 243 



of the highest temperature. The thermometer which 

 records the lowest temperature of the night is usually 

 filled with spirit instead of mercury, and has a small 

 metal index immersed in the spirit. As the temperature 

 falls the index is carried down by the spirit, but when the 

 temperature rises again the spirit flows past the index, 

 leaving it to register the lowest temperature attained. 



The instrument which measures rainfall consists of a 

 copper cylinder four to six inches high, with a funnel- 

 shaped bottom, fitting into the top of a ' splayed ' copper 

 vessel firmly fixed in the ground. A glass vessel is placed 

 inside the base below the funnel to catch the rain-water. 

 The observer takes off the funnel and pours the water 

 from the glass vessel into a measuring-glass, on which 

 he reads the amount of rainfall since the last observation, 

 in inches or millimetres. The result is recorded in the 

 observer's register, and in the case of a station which 

 reports by telegraphy it is included in the message to 

 Adastral House. 



Sunshine is measured by burning. A clear glass ball is 

 partly encircled by a metal belt at a distance of about an 

 inch. Fitted into this belt is a blue card marked off in 

 sections by white lines, each line representing one hour. 

 The sun's rays are caught by the ball and focused on to 

 the blue card, where they trace a thin burnt line into it. 

 Thus, if there are four hours of continuous sunshine, a line 

 is burned across four sections of the cord. If the sun is 

 obscured, the point of the card which would have been 

 under the rays at that moment is unburnt. 



" Visibility good," says a weather report. What does 

 the phrase mean ? At Kew Observatory one may learn. 

 Standing on the roof, the observer takes local landmarks 

 as guides. Thus thick fog at Kew means that a shed a 

 few feet from the building is hidden. A near-by church is 

 another point ; the Richmond golf club-house is another. 

 Each point has its corresponding state of visibility — 



