584 REPORT— 1900. 



Hora of a district, and their7observation with this object was a matter 

 which might well be recommended to all local scientific Societies. 



Mr. Vaughan Cornish said that in Berkshire the dew-ponds were 

 frequently in open situations and not under trees. He would bi'ing the 

 matter before the notice of the Dorsetshire Field Club, and he hoped they 

 might be able to make some systematic observations on dew-ponds. 



Mr. John Hopkinson noticed that Professor Miall held that the margin 

 of the jDond had very little effect in increasing the amount of rain col- 

 lected, but he believed that, as a rule, the area of the margin was at least 

 equal to that of the surface of the pond. There was thus twice the 

 area for rainfall that would be given if the water-covered surface alone 

 were reckoned. It was difficult to form an idea as to how water was 

 contributed to these ponds by dew, as dew would require a surface cooler 

 than the air oh which to condense, whilst the water in the pond would 

 usually cool more slowly than the air above it. The water being also 

 warmer than the surface of the ground surrounding it, dew would not 

 so readily condense on it. He believed that observations had been 

 made, but he was not aware that any one had actually seen the dew 

 accumulating on the side of a pond and trickling down into it. The 

 margin had certainly very little, if any, effect as regards the amount of 

 dew received. A distinction must be drawn between dew and mist : 

 the latter would probably increase the amount of water in a pond. As 

 to the level of these ponds, he believed that it varied considerably from 

 time to time. Where there were trees overhanging the pond there would 

 be a considerable deposition of dew, but he thought that the majority of 

 these ponds were not surrounded by trees. As to evaporation from 

 tlie ponds, mist was to be seen at times rising from their surface. He 

 believed that the average rainfall where dew-ponds were situated was 

 between twenty-five and thirty inches per annum. But there were 

 scarcely any rain-gauges on the high ground where dew-ponds existed, 

 and there was probably more rain on the hills than in the valleys. He 

 did not know of any dew-ponds in Hertfordshire, though there was a 

 considerable area around Royston and Hitchin where there was bare 

 chalk. He thought the subject extremely interesting, and one which 

 might be profitably studied by the local Societies. Among other results 

 their investigations might some day enable farmers to fix upon the best 

 possible sites for their dew -ponds, and so prevent the waste of a consider- 

 able amount of money. 



Mr. Clement Reid remarked that the ponds which had stood the severe 

 drought had generally trees on their margin. 



Mr. J. Brown said that in order to form an accurate estimate of what 

 was gomg on it would be necessary to consider the amount of water con- 

 sumed by the animals drinking at the pond. There were no dew ponds 

 in Ireland. 



The Chairman remarked that dew-ponds were only made in a country 

 like that of the higher chalk districts, where the rocks were absolutely dry. 



Mr. W. Gray said that there was a great deal of superstition about 

 water, and some of the accounts of dew-ponds which never failed, &c., 

 probably owed much to that source. There were wells in Ireland the 

 water of which it was said would not boil, and the people never used 

 it for cooking, because they thought that it would be useless for that 

 purpose. This notion evidently arose from the fact that the water from a 

 deep-seated source is of the same temperature in summer and winter, and 



