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 : b 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 

 and 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 be 



