e carried fifty feet, with a rise of not more than six inches, and
the draft will then be sufficient.

The dimensions of the flue may vary from 8 to 12 inches in width, and
from 12 to 18 inches in height, according to the space required to be
heated. The usual mode of construction, when bricks are used, is to lay
them crosswise and flat for the bottom and top, and to set them edgewise
for the sides. Tiles for the bottom and covering are an improvement upon
bricks: being thinner, the heat passes through them more readily, while
they still retain the heat sufficiently to equalize the temperature.
Tiles used for the top covering are sometimes made with circular
depressions for holding water for evaporation.

STEAM.--The employment of steam for heating green houses, graperies,
&c., is almost entirely superceded by the hot water method. It will,
therefore, be necessary only to allude briefly to this part of our
subject. It occasionally happens that a conservatory attached to a
dwelling is heated by the same steam apparatus employed to heat the
latter, but we believe that a person who should advocate, at the present
day, the general adoption of steam as a means of heating horticultural
structures, would be regarded as belonging to a generation which has now
passed away.

Steam travels through pipes with great rapidity, and parting with its
heat rapidly, it becomes quickly condensed, unless the boiler is of
large capacity and capable of furnishing a full supply. It is, at best,
an unsatisfactory mode of heating plant houses, for if from any cause
the water in the boiler is reduced below the boiling point, the steam in
the pipes is instantly condensed, and with it all heat, except that
remaining in the iron of the pipes, and the condensed steam, is
withdrawn.

Hood, an English author on heating, quoted by McIntosh in his valuable
work the "Book of the Garden," thus compares the merits of steam and hot
water. "The weight of steam at the temperature of 212 deg. compared with the
weight of water at 212 deg., is about as 1 to 1694, so that a pipe that is
filled with water at 212 deg., contains 1694 times as much _matter_ as one
of equal size filled with steam. If the source of heat be withdrawn from
the steam pipes, the temperature will soon fall below 212 deg. and the steam
immediately in contact with the pipes will condense: but in condensing,
the steam parts with its _latent heat_ and this heat in passing from the
latent to