100 
UPON THE APPLICATION OF HOT WATER IN HEATING 
HOT-HOUSES. 
BY MR. THOMAS TREDGOLD. 
Extracted from his Paper read before the London Horticultural Society, August 5, 
1828, and inserted in their " Transactions," Vol. 7, p. 568. 
The power of imitating other climes and other seasons than those which nature 
affords us, is known and valued as it ought to be ; yet it remains difficult even to 
imagine the extent to which this power may be applied. In this age it produces 
luxuries of which few can enjoy more than the commonest species ; but in the next, 
nay, even in our own, there is a reasonable expectation of a considerable addition to 
the quantity and quality of those artificial productions, as well as to the best sources 
of pleasure and information they afford to the admirers and students of nature. 
The obvious advantages of the hot water system are, — 1st, the mild and equal 
temperature it produces, for the hot surface cannot be hotter than boiling water ; 
2nd, the power of heating such a body of water as will preserve the temperature of 
the house many hours without attention ; and, 3rd, the freedom from smoke, or other 
effluvia of smoke flues. In houses appropriated to plants, these advantages are 
most important. 
In order to develop the principles on which a hot-water apparatus acts, we may 
select the simple case of two vessels placed on an horizontal plane, with two pipes 
to connect them ; the vessels being open at the top, and the one pipe connecting 
the lower parts of the vessels, and the other their upper parts. 
If the vessels and pipes be filled with water, as fig. 1, and heat be applied to 
vessel A, the effects of heat will expand the water in the vessel A, and its surface 
will, in consequence, rise to a higher level {a, a), the former general level surface 
being b b. 
Fig. 1. 
; IgMiBSf 
b 
The density of the fluid in the vessel A will also decrease in consequence of its 
expansion ; but as soon as the column c d of fluid above the centre of the upper 
pipe is of a greater weight than the column f e, above that centre, motion will 
