10 



MR. Thompson's experimext. 



feet Mgh, without any pit in the middle ; the result of my observations 

 on those two houses, and the quantity of fuel required by each of them, 

 was as follows : The iron-roofed house with eighteen degi'ees of frost, 

 required nearly six bushels of coals, and unremitting attention during the 

 night and until three o'clock in the moridng, while scarcely three bushels 

 were consumed in keeping the vinery at the same degree of temperature, 

 no attention being required after ten o'clock, at which time the fires were 

 made up and left for the night. 



Being determined to investigate thoroughly the merits of the two 

 materials, I caused one house, constructed of wood, and another of iron, of 

 precisely the same dimensions as regards the superficial feet of glass, to 

 be perfectly repaired, in the autumn of 1832, and on having them examined 

 and repaired in the following season, I found that the cost of repairing 

 the iron house was nearly double the sum required to repair the wood 

 one, which I attributed to the expansion of the iron in summer and its 

 contraction in the winter. From these and other experiments I have had 

 opportunities of making, I have arrived at the conclusion, that wood has 

 the advantage over iron in four xery essential points, viz., the saving of 

 fuel, glass, and labour. I have also found it conducive to the better growth 

 of plants and fruits, as I have never found the plants thrive so well or 

 look so healthy in an iron, as in a wooden-roofed house, 



"I am aware that for lightness of appearance in the structure, iron has 

 hitherto had the advantage, but I am confident that if proper attention 

 were paid to the erection of hot houses, and to the materials used in their 

 erection, the appearance of the wood roof would be less objectionable, and 

 for the assistance of persons of less practical experience than myself, I here 

 give a brief description of the materials and mode of construction I would 

 recommend, as combining all the desired objects. The first thing to be 

 attended to is, to give the roof a proper pitch or incUnation, so as eflfect- 

 ually to cany off the water, and to prevent drip into the house, which is 

 liighly injurious to all plants, particularly to those grown in pots ; the 

 rafters should be of wood, varying according to the length of the roof, 

 from six to eleven inches in breadth, and the section of the rafter should 

 be wedge-shaped, from three to four inches wide on the 

 upper side, where the lights rest, and about half an inch 

 wide on the under side. The strength of all rafters depend 

 more on their depth than thickness. The shade would be 

 also less. The four sides of the hghts (all made of wood) 

 should be as follows, — the top should be from five to six 

 inches wide, the sides two and a half inches, and the bottom from six to 



