ON CURVILINEAR IRON ROOFS TO HOTHOUSES. 265 



ventilation, by giving (plate' 1 ?) a slight sketch of the form of a section of 

 my house, in which D marks the position of cylindrical passages 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 each end of the house, and I had the satisfac- 

 tion to observe, that the temperature of that part of the house in which 

 the thermometer stood was raised between two and three degrees, when 

 the external air was at 40. This effect was, I conclude, produced by the 

 heated air being impelled into the body of the house amongst the 

 plants, instead. of being permitted to rise, as it had previously done, and 

 to come instantly into contact with the roof : and by suspending light 

 bodies amongst the plants, I ascertained that the previously confined 

 air was thus constantly kept in a state of rapid motion. The air is 

 suffered to escape through passages of four inches wide and two inches and 

 a half high, at E, which passages are placed at the same equal distances 

 as those in the front wall, and, like those, are opened or closed as circum- 

 stances require. The trouble of opening or closing such passages, after 

 substances of proper form are prepared and suspended for the purpose, 

 is very small, much less, I think, than that of moving the lights of any 

 house of ordinary construction ; and the effect of the kind of ventilation 

 obtained upon the growth of my plants and fruit, is everything I wish 

 it to be. 



I have stated that my whole house is heated by a single flue : this 

 enters at the west end of it, and thence passes along the whole front 

 within sixteen inches of the wall. It then returns twenty feet towards 

 the middle of the house and back again, the smoke escaping at the end 

 opposite to that which it enters. The flue is consequently single at the 

 end of the house, which adjoins the fire place, and triple in the last 

 twenty feet of the opposite end ; by which means a nearly equal 

 temperature is everywhere given. 



