the diagram at p. 18, and the description of it at p. 20, I have
indicated and recommended a plan of moistening the soil by pouring water
down beneath the soil: this was to be done by the help of tubes provided
for the purpose. The soil was supposed to rest on the top of the hot
water-tank, which was to supply bottom heat; and immediately beneath the
soil, a layer of open rubble was proposed to be placed, among which the
water applied might find its way, and gradually moisten the superincumbent
soil. Mr. Hunter, gardener at Mawley Hall, in detailing[3] his sixteen
years' experience in tank-heating, has in great measure corroborated
these views; and as his corroboration of the plan I have recommended,
embodies some useful hints, I will quote the substance of his remarks:--"I
had a pit erected, thirty-eight feet long, seven and a half wide, divided
into four compartments, for growing melons and cucumbers, with a tank
extending the whole length of the pit, six feet wide and six inches deep.
Across this I put larch spars, and upon them turves, with the grassy side
downwards, and on them the soil for the melons and cucumbers. The plants
grew and did well for a time, but they were of short duration in
comparison with the dung-bed. Instead of the moisture ascending through
the soil as I expected, I found that the heat from the tank dried the
turves and soil next to them as dry as dust, and that there was no such
thing as obtaining a moist heat from hot water without the soil was in
contact with it. Next year I put broken stones upon the spars, and turves
upon them, and made my arrangements so that I could occasionally run water
in the tank to wet the turves and the soil next them. This was an
improvement; and I went on prosperously for some years, till the spars
began to decay. I then had iron bars put across, and two of the
compartments covered with squares, a foot in diameter, and one inch thick;
the other two with slates; both slates and squares jointed with Roman
cement, to prevent the soil from getting into the tank, as I had found the
inconvenience of it when using the spars. I put some broken stones upon
the covers, and turves upon them, and then the soil. Here my original
difficulty occurred; the soil next the covers got too dry, and to moisten
it from above was impracticable, without making the soil a complete
puddle, which would have stopped the healthy growth of the plants. To
remedy this, I put six small earthen pipes