METHODS OF VENTILATION. 279 



in England. Fig. 54 represents the end section of the house, 

 with the ventilator in proportion to the other parts. Fig. 55 



Fig. 55. 



shows the sectional view of the ventilator, enlarged : a a sue 

 openings of admission, and are covered with lattice-work, to 

 break the force of the current of ingress ; b, the movable shut- 

 ter, which regulates the admission to and egress from the house. 

 It is scarcely necessary to observe that these houses have been 

 ventilated on the most approved principles; and it appears 

 that several advantages are gained by this method. For in- 

 stance, the current of heated air is arrested, in its progress 

 outwards, by the depending glass at c c, and is, in some meas- 

 ure, thrown downwards, preventing also the escape of its con- 

 tained moisture. There is no doubt this method is very com- 

 mendable for span-roofed houses ; and one of its advantages is, 

 that the house can be aired, at any time, without the plants 

 being saturated with rain. 



It is very possible that these compound systems of ventilation 

 may excite a smile from some who have, all their lifetime, been 

 accustomed to pull heavy sashes up and down for the purpose 

 of giving air. But if we include, in one computation, the 

 labor, the time, and the advantages of giving a range of houses 

 three or four hundred feet long, air at the proper time, and all at 

 the same moment, we will find a value in the system worthy of 

 something more than the mere smile of passive silence, which 

 is too frequently all that is at first accorded to such improve- 

 ments. 



In some establishments, instead of pulleys, toothed wheels are 

 fixed to the shaft, which are made to work in a curved handle 

 24* 



