302 FORCING GARDEN. 
apparatus placed at the head of it; but this method, being 
complicated, has given way to several modifications, in 
which the door a has been found the most useful, the fuel 
being pressed forward by the common tools used for feed- 
ing furnaces: 8 is the door for regulating the fuel on the 
grate c. In its progress, the whole surface of the coal 
along the inclined plane is constantly kept in a state of 
inflammation, the flame having naturally a tendency to burn 
upwards. In this way, the greater part of the fresh coal 
is carbonized, that is, the gas is separated from it and in- 
flamed, leaving only coke. The strong combustion of the 
coke at the grate produces heat enough to carbonize the 
coal, and air enough to inflame the gas. This furnace, 
therefore, not only consumes most of the smoke, but effects 
a considerable saving of fuel. 
Steam.—Of late years steam has been applied with suc- 
cess to the production of an artificial climate -in glazed 
houses. It is more genial than fire-heat from flues, being 
less :contaminated, and more equable and pliant in its 
distribution. In steam hot-houses, the plants can scarcely 
ever be liable to suffer from scorching heat; the air con- 
tinues pure and untainted, and persons visiting the house 
are much less liable to be annoyed by the smell of smoke 
and soot. It is neater in all its arrangements within doors 
aud also without, for it precludes the necessity of more 
than one furnace, and one chimney-top, and in a great mea- 
sure removes the unseemliness of the heaps of coals and 
ashes with which common furnaces are usually surrounded. 
In districts where coals are dear, the saving of fuel is an 
object ; and it has been found that seven bushels of coal 
go as far in keeping up steam heat as ten bushels do in 
maintaining an equal temperature in the ordinary way. 
By merely opening a valve, the house may at any time ba 
