Report (in Tern per at are and llfdnfnll. 81 



from observations taken in the district, that in clear weather the 

 air in contact with the ground is sometimes cooled and rendered 

 denser by radiation, and gradually descends the hills to low- 

 lying grounds, displacing the warmer air below, and in this way, 

 by the accumulation of cold air in the valley of the Wandle, in 

 fine di-y weather the temperature at Beddington and Waddon is 

 lowered at night below that of the other stations. Moreover, 

 this hypothesis is confirmed by the table of relative humidity 

 computed from the West Norwood observations, from which it 

 will be seen that, roughly, the degree of humidity varies 

 inversely as the extent of depression of temperature at the 

 lower stations. Comparing Park Hill with Beddington, in the 

 seven mouths ending March, the average minimum temperature 

 at Beddington was less than that at Park Hill by l°-8, the 

 contemporaneous degree of humidity at Norwood having been 

 87 ; but from April to August, when the degree of humidity at 

 Norwood was only 75, the average minimum temperature at 

 Beddington was lower than at Park Hill by 2°-5. The driest 

 month of all was July, 1881, and on that occasion the average 

 difference amounted to 3°-5 and the extreme to 7°'l, and in 

 January, 1881, the driest of the Januarys, the differences were 

 respectively 2°'5 and 5°'8. 



Conditions resembling these as regards the distribution of 

 temperature exist without doubt in the valley of the Eavens- 

 bourne. In fact, very low temperatures have been recorded in 

 the more contracted parts of the valley, as at Catford Bridge, 

 the latent heat evolved on the descent of the air and its coming 

 under higher pressure and contracting in volume being insuffi- 

 cient to counteract the cold produced by radiation. 



At Chelsham, where temperature observations for two years 

 and nine months are available for comparison, the average was 

 1°'85 less than at the Croydon stations for the corresponding 

 period, showing a diminution of temperature at the rate of 1° per 

 231 feet increase of elevation, and the daily range of temperature 

 was less at Chelsham by 0°-5. 



As compared with the temperature of the air, the rainfall has 

 been far more extensively observed in the Club district. Nearly 

 all the hill stations were established several years ago, by Mr. 

 Baldwin Latham, by whose assistance it has alone been possible 

 adequately to investigate the rainfall of the North Downs. Mr. 

 G. J. Symons, the well-known authority on British rainfall, has 

 kindly permitted free use to be made of his annual publication, 

 and wherever temperature observations were taken the rain was 

 also observed. 



In tabulating the returns, when two or more gauges have been 

 maintained at the same place, only the records of the one 



