On curvilinear Iron Roofs to Hot-houses. 229 



perfection at all seasons ; provided the flues operate with 

 sufficient power to give the requisite temperature. But in 

 my house, with a curvilinear roof, I acquired the power of 

 almost wholly preventing any change of air whatever, and I 

 exercised that power too extensively, after the fruit was 

 shown, and particularly after a part of it had nearly ac- 

 quired maturity. In the last spring I adopted a mode of 

 ventilation, from which I expected to derive all the advanta- 

 ges of change of air, without materially lowering the tempe- 

 rature of the house, and the success of it has greatly 

 exceeded the expectations I had entertained. I shall best 

 be able to shew the advantages of this mode of ventilation, 

 by giving a slight sketch of the form of a section of my 

 house, in which D, marks the position of cylindrical passa- 

 ges of nearly two inches diameter through the front wall. 

 Through these, which are placed eighteen inches distant from 

 each other, along the whole front wall of the house, the air, 

 whenever the weather is warm, is suffered to enter freely, 

 and its entrance is at other times more or less obstructed in 

 proportion to its coldness : but it is never wholly excluded, 

 except during the nights in very severe weather. 



The passages through the front wall are placed at just 

 such a distance from the ground, as will occasion them to 

 direct the air, which enters, either into contact with or to pass 

 closely over, the heated covers of the flue. It consequently 

 becomes heated, and is impelled amongst the Pine apple 

 plants, which stand in rows behind each other, each row of 

 plants being so far elevated above that before, as to place 

 every plant at nearly an equal distance from the glass roof. 

 A thermometer was placed at H, being equally distant from 



