SOME DEW-PONDS IN DORSET. 31 



Messrs. Hubbard, in the 2nd Edition of their work, give a 

 most interesting chapter on dew-pond experiments. These 

 they carried out on rather a large scale. They obtained 

 a suitable site and excavated the ground over a space of 100 

 feet square, thus obtaining a superficial area of 10,000 feet. 

 The excavation was carried to a uniform depth of 1ft 6in., 

 and a layer of 4in. of concrete was laid over the whole. 



Upon this they put a coating of pitch or tar to stop any 

 moisture from below from penetrating through the concrete 

 to the layer of non-conducting material they intended to 

 lay upon it, spreading dried sand over the tarred surface. 



For this non-conducting layer they used mica, which is a 

 well-known non-conducting medium ; on this was laid a 

 coating of asphalt to bind the whole upper surface together. 

 This was successful to a certain point, namely, that their pond 

 gathered a considerable quantity of water by night, though 

 no rain fell, which was lost by evaporation by day. The 

 rainy season having set in they were obliged to postpone 

 their experiments until the following summer. 



Unfortunately, through an accident, the asphalt got 

 damaged in several places, thus admitting the water to the 

 layer of mica, reducing it to a useless pulp, so that the experi- 

 ment had to be abandoned. 



Further experiments were conducted by Mrs. George 

 Hubbard on ponds constructed on the same principle, but 

 employing different materials, but though the results she 

 obtained were encouraging, they failed to prove that water 

 in any considerable quantity could be collected from dew, 

 on the principle upon which they sought to prove that 

 Neolithic man obtained his water supply for his camps 

 situated in elevated positions on the tops of our downs, where 

 they are usually to be found. 



From some interesting experiments conducted by Mr. J. 

 G. Cornish on the Berkshire Downs in January, 1910, it was 

 found that after a night of fog the surface of his pond had 

 (on January 18th) risen 1J inches ; the next day, following 

 another heavy fog, it had risen no less than 2 inches, and on 



