l82 



Harvest Weather Forecasts. 



[JUNE, 



larger it is, even though no rain may fall. If such a structure 

 is situated on the summit of a down, during the warmth of a 

 summer day the earth will have stored a considerable amount 

 of heat, while the pond, protected from this heat by the non- 

 conductivity of the straw, is at the same time chilled by the 

 process of evaporation from the puddled clay. The consequence 

 is that during the night the moisture of the comparatively warm 

 air is condensed on the surface of the cold clay. As the 

 condensation during the night is in excess of the evaporation 

 during the day, the pond becomes, night by night, gradually 

 filled. Theoretically, we may observe that during the day the 

 air being comparatively charged with moisture, evaporation is 

 necessarily less than the precipitation during the night. In 

 practice it is found that the pond will constantly yield a supply 

 of the purest water. 



"The dewpond will cease to attract the dew if the layer of 

 straw should get wet, as it then becomes of the same temperature 

 as the surrounding earth, and ceases to act as a non-conductor 

 of h'eat. This practically always occurs if a spring is allowed to 

 flow into the pond or if the layer of clay (technically called the 

 ' crust ') is pierced." 



During the harvest season the Meteorological Office will, 

 as before, supply forecasts of weather by telegraph to persons 

 desirous of receiving them, upon payment 

 Harvest Weather Qf ^j^g ^.Qgt of the teles^rams. The forecasts 

 Forecasts. .„ , 11,, r ^ 



will be so worded that the cost of each 



message will be 6d. for any one district, including an address of 

 three words. If the address to which the forecasts are to be 

 sent exceeds three words, an addition of a halfpenny for each 

 additional word must be made to the cost of the daily telegram. 



The harvest forecasts are prepared at 3.30 p.m. daily from 

 June I to September 30 (except Sundays), and are applicable 

 to the twenty-four hours from midnight following the time of 

 issue. 



Applications for the forecasts may be made on a form which 

 can be obtained from the Secretary, Meteorological Office, 

 63, Victoria Street, London, S.W. 



