VENTILATION WITH FANS. 331 



50, the air entering should not be under that temperature, but 

 rather a few degrees above it. 



4. If the house be heated by pipes laid round the side of the 

 house, the air thus admitted should be introduced so as to pass 

 upward, by the side of the pipes, on entering the house. This 

 air should pass regularly and consentaneously upwards ; not in 

 sudden blasts and currents, which have always an injurious 

 influence on the internal atmosphere. 



To effect this, a hot-air chamber should be placed in connec- 

 tion with the heating apparatus, from which must be laid air 

 channels, or conduction tubes, all around the house, having 

 apertures for the egress of the air, at distances of six or eight feet 

 apart. Within this chamber a fan might be used for drawing 

 in the external air and driving in the warmed air through the 

 tube. This fan might be driven by a small windmill con- 

 structed for the purpose. 



When air is under the control of a moving power, it will take 

 any direction that is desired. It will move horizontally, or ver- 

 tically, either upwards or downwards, and even in both direc- 

 tions, at the same time. 



It is essential, however, that the supply to be warmed should 

 be drawn from the external atmosphere ; and here the fan may 

 be used to great advantage. In no case should the supply of air 

 be drawn from the interior of the house. The vitiated air, as it 

 passes upward, should be allowed to pass off freely into the 

 atmosphere. 



In this country, however, the fan cannot be so advantageously 

 applied in the ventilation of horticultural buildings, as in north- 

 ern Europe, and only at night, the period when ventilation is 

 most needful. The large amount of artificial heat necessary in 

 our New England climate, in severe nights, is more injurious to 

 green-house plants than the excessive heat of summer. There 

 is no impossibility, however, in producing a constant and equa- 

 ble motion in the atmosphere of green-houses, at night ; and 

 this may be effected by the means which we have just ex- 

 plained. 



Fans may also be beneficially employed in producing a cool- 

 ing effect in the air at the top of the house. The injurious 



