194 



A Chapter on Greenhouses. 



it may be easily accessible in all weathers. It has an ornamental sash at 

 the sides, at tlie bottom, and also at the top under the cupola. 



Ventilation is obtained by opening a portion of the bottom sash at the 



sides, and all the side sash in the cupola. The ventilating sashes are ope- 

 rated by means of a shaft the length of the house, with arms attached by 

 rods to each ventilator, all opening simultaneously : the shaft is operated 

 by means of a spiral screw and gear, which returns the ventilators in the 



