57 
ON 
THE RELATIVE MERITS OF IRON AND WOOD ROOFS, 
FOR STOVES, GREENHOUSES, &c. 
(Continued from page 40.) 
Having I think fully shown the advantage possessed by wood over cast-iron 
in these very essential points — the better growth of plants and the saving of fuel, 
glass, and labour, — I shall now add to these observations a few words on the 
various systems of heating houses, that is to say, by common flues, with steam, 
and by the circumvolution of hot water. The last-named method is now 
become very general, and is admitted by all scientific men to be the best, because 
it is the safest, the most certain, and no doubt, when fitted up on a good principle, 
it is also the most economical, as regards the expenditure of fuel and the applica- 
tion of labour. Entering therefore on this all-important subject, I shall confine 
my observations, in the first place, to the advantages of hot water over steam, 
which are in my opinion many and very great, particularly where coals are ex- 
pensive ; for, to generate steam, an enormous consumption of coal or oven-coke, 
which is nearly as expensive, is indispensably necessary, as a weaker fuel will be 
found of no avail. This is the first evil of the steam system ; and the second is, 
that a man's time must be nearly if not wholly taken up in affording that con- 
stant attention which is required to keep up the fire. Then, in the third place, 
there is a considerable loss not only of time but of fuel also, before the pipes 
become filled with steam. This is a very important fact, to which perhaps due 
attention has not been paid, for it may not be generally known, that steam travels 
through the pipes in a time no shorter than it requires to make them nearly as hot 
as itself ; for steam, the instant it comes in contact with a body colder than itself, 
becomes condensed, and its onward motion is of course impeded. Again, the 
moment the fire becomes too weak to keep the water at the boiling point so that 
steam may be generated, it immediately ceases to furnish heat to the pipes, conse- 
quently they soon become cold ; and this is the fourth evil of heating by steam, 
which is avoided by the use of hot water, for the instant the fire is ignited and the 
water gets warm, the particles of the fluid are set in motion, circulation in the 
pipes commences, and continues until the whole of the fluid is consumed, or so long 
as there remains any heat in the furnace, in the bricks, or in the boiler. Still 
further, I have proved that pipes each 4 inches in diameter, when filled, the one 
with water at a heat of 200 degrees, and the other with steam, the one with hot- 
water would contain a much greater and more enduring body of heat than the one 
filled with steam ; and I have no doubt, that if, when both pipes were heated up to 
the stated temperature, the fires were suffered to expire, the pipe containing steam 
would cool as much in one hour, as the hot- water pipe would in six or seven hours. 
vol. v. — NO. LI. I 
