VARIOUS METHODS OF HEATIXG DESCRIBED IN DETAIL. 247 



as the case may be, for the supply of the mansion, and the 

 several hot-houses, all of which are heated by the same appara- 

 tus. Here the air is moved and replaced, not only by its own 

 density, as in the common methods of hot-air heating, but it is 

 drawn rapidly inwards by the suction of the fan on the one side, 

 and driven onward by its propulsive power on the other ; and 

 thus it appears the heat travels with great rapidity, and within 

 a few minutes after the heated air is turned on the apartment, 

 and moistsned as may be desired by the jet of steam already 

 described."^ 



* Fans are now frequently employed for effecting ventilation, and 

 are generally connected with the heating apparatus. They have never, 

 as far as we know, been employed for this purpose in any kind of hor- 

 ticultural structures, although we can see no reason why they should 

 not be so. This will be again referred to, when we come to treat on 

 that part of our subject. 



