Notes and Comments. 155 
Previous to that, the stock grazing on the open commons were 
driven to be watered at the ponds in the villages. These 
ponds are mostly of a circular form and of all sizes, from ten 
yards to fifty yards in diameter. A few are oval, to adapt 
themselves to the ground on which they are constructed.’ 
THEIR SITES. 
‘Their chosen sites are generally in depressions on the’ 
surface of the land, in which the rain-water has a tendency to 
collect, or on sloping ground, and often near the side of a high 
road or track-way, where the running water from the roads 
during rain can be conveyed by a channel or gutter into the 
pond. This is the means by which the ponds are supplied on 
the Yorkshire Wolds. No one ever thinks of filling them by 
any other means, the condensation of a fog or mist being a 
very small factor.’ 
THEIR CONSTRUCTION. 
“In this district they are constructed as follows :—Fiurst, 
a dish-shaped excavation with a gentle slope to the centre, is 
made in the ground, to the depth of 4 to 6 feet, according to 
the diameter of the pond. This is then covered with quick 
lime, next a layer of clay, which is wetted and beaten with 
wooden mallets into an impervious sheet, 3 to 4 inches thick. 
Again a covering of quick-lime is applied, then a coating of 
stiff wheat-straw, and on the top of this is spread broken chalk. 
The two coverings of lime are to prevent earth-worms boring 
through the bed of clay. The bed of straw is to prevent the 
covering of broken chalk from being trodden, by cattle going 
to drink, into the impervious bed of clay, which, if not pro- 
tected by the straw and broken chalk, would be pierced through, 
and the pond would lose its water. I believe it is generally 
considered that, as soon as the pond is constructed, the sooner 
it is filled with water the better, as, if without water for any 
length of time, the clay lining is liable to shrink and crack from 
the effect of dry weather.’ 
ACTION OF LIGHT UPON CHLOROPHYLL. 
At a recent meeting of the Linnean Society, Mr. Harold. 
Wager read a paper on‘ The Action of Light upon Chlorophyll.’ 
‘ By making a film of chlorophyll, upon paper and on glass, 
by floating an alcoholic solution, and allowing it to dry, the 
author was able to bleach a portion under strong sunlight, 
and covering a portion by black paper ; when this was tested 
by Schiff’s solution, the exposed, that is the bleached portion, 
became pink, the unexposed portion showing no colour change. 
Another experiment was made by subjecting similarly bleached 
portions of chlorophyll to the action of potassium iodide, when 
the exposed parts turned reddish-blue, in consequence of the 
liberation of iodine, which acts upon the starch on the paper. 
1915 May 1. 
