SECTION VIII. 



VENTILATION WITH FANS. 



In a preceding part of this work, [see Part II., Sec. V.] we have 

 described a method of warming hot-houses practised in Ger- 

 many, in which a fan is used as a means of propelling the 

 heated air into the apartments required to be warmed, and by 

 which the volume of air to be heated is drawn from the external 

 atmosphere. As an auxiliary to a heating apparatus, however, 

 the complicated arrangements of this machine, the cost of its 

 construction, and the expense and trouble of working it, must 

 ever continue to prevent its adoption as a method of warming 

 horticultural buildings, however extensive they may be. But as 

 an auxiliary of ventilation, and as a means of creating that con- 

 tinual motion in the air, which some cultivators so much admire, 

 it is undoubtedly superior to all other methods. 



Fans are so common as to require very little description. The 

 kind of machine generally used for this purpose is merely a 

 light circular kind of wheel, composed of as many vanes or blades 

 as the size will admit. By the constant revolution of this w^heel, 

 a movement is created in the atmosphere, which causes a change 

 in the position of the atomic particles of the atmosphere of the 

 room in which it is at work ; but does not, as some suppose, 

 tend to its equalization. 



Fans are of t\vo kinds, and have different methods of action. 

 The one is termed blowing fans ; the other, exhausting^ or suction 

 fans. In the first case,, the air in the house is driven outwards 

 from the fan, or blown away ; in the other, it is drawn towards it. 

 It will appear evident, however, that, in applying this machine 

 to the creation of a movement in the atmosphere of a hot-house, 

 various requisites must be had, namely, a moving powder, con- 

 stantly and steadily acting, and completely under control ; and 

 when it is to be applied to night ventilation and motion, which 

 appears to us the most adaptable use to which it can be applied 



