TRANSACTIONS OF SECTION E. 531 
so-called dew-ponds of the south of England are kept full, or partly so, by dew. 
A dew-pond is a pond, generally on the chalk downs, which has no visible means 
of replenishment other than rain, and as such ponds as a rule maintain a supply 
of water during a long spell of hot weather, when most of the ponds at lower 
levels have dried up, the conclusion has been drawn that they have been 
fed by dew, and that this dew has been sufficient to prevent them being dried 
up. The name is quite modern, and even Gilbert White, who wrote about 
their peculiarity, does not call them by that’ name. It is probable that in 
the popular mind any form of condensation out of the atmosphere has been. 
regarded’ as dew, and that really these ponds are ‘mist-ponds.’ As regards 
the foundations of such ponds there is no uniformity. The author found no 
fewer than ten different arrangements of the bottoms of the ponds. | Many 
of them had straw as part of the foundations, but no practical pond-builder: 
contended that this had anything to do with the . condensation of dew 
into the pond. Straw is a bad foundation on which to puddle clay or chalk, 
and must necessarily become damp in the process, and so become a fair conductor 
of heat. In order to test the theory that straw would prevent the heat of the 
earth from rising-and warming the pond after nightfall, two ponds were made, 
in one of which the puddle was laid direct.on.the straw, and in the other planks 
were inserted between the straw and the puddle, in order to give a firm base. 
Experiment went to show that in neither case was there any appreciable effect as 
regards dew-deposition. This was probably so because, as pointed out by 
Dr. J. Aitken, such a foundation would tend to make the water take a higher tem- 
perature during the day, and this would be in direct proportion as the bad heat- 
connection was effective during the night. The water would not have sufficient 
time as a rule during the short summer night to become reduced below. dew-point.. 
The experiments made only refer to those ponds which have no trees or bushes 
growing around them which would prevent free radiation. It is not denied that 
there would be considerable drip from trees, &c., which would feed a pond, but 
this means of replenishment would be of a different nature from that which, it 
had been supposed, a pond would receive when the grass of downland around was 
seen to be drenched with dew. There may be heavy dews upon the grass, but 
there may be none whatever deposited in the pond. It has been suggested that 
there may be upward percolation of water from the soil into the pond in dry 
weather, and the state of the puddle when the pond was dug up seemed to show 
that to some extent this may be the case. On the other hand, there may have 
been escape of the water downward, for it is probably impossible to make a pond- 
bottom completely watertight. It is found that if precipitation and evaporation 
were equally spread over the year, a pond which was well laid would never dry 
up. But nine-tenths of the annual evaporation takes place in the summer 
six months, whereas rain is irregular in its distribution. The evaporation 
would actually empty some ponds in the summer months if there were not some 
other form of condensation which assisted in overcoming the concentration of 
evaporation duiing the droughts. The author sees in fogs and mists the factor 
which tends to keep alive the best-made of the ponds. The precipitation of mist 
into ponds, aided perhaps by silent discharges of electricity, and the entanglement, 
of mist-laden salt-dust in the hollows in which the ponds lie, are believed to be 
the means by which some ponds maintain a supply of water all through the year, 
in spite of the great draught which is made upon them by numerous cattle. 
2. Antarctic Discovery. By Sir Cuements R. Marxuam, K.C.B., 
F.R.S. (Opening a Discussion on the Antarctic.) 
The Antarctic work which formed the subject of this Paper was solely that 
which was sketched out by Sir John Murray in 1893—the exploration of the 
southern continent. It did not refer to voyages of ships in the south temperate 
zone or a little to the south of the Antarctic circle, nor did it refer to mere 
dashes to the South Pole. 
The true Antarctic expeditions, with which alone the Paper was occupied, are 
those whose main objects have been the exploration of the southern continent, 
those of Captain Scott, Mr. Mawson, and Captain Filchner. 
MM 2 
