50 ON THE MERITS OF IRON AND WOOD FOR ROOFS 



submit to your consideration the result of my practical observa- 

 tions relative to the two description of houses under consideration 

 as a guide to persons who may be inclined to raise such erections, 

 but are unacquainted with the injurious consequences of ill-con- 

 structed hothouses for horticultural purposes. Having had fif- 

 teen years practical experience with, and the management dur- 

 ing that long period of about three thousand running feet of 

 glass, designed for the culture of fruits and plants, enable me 

 to speak with some decision on the subject; and there are, I 

 doubt not, hundreds of practical gardeners, who will confirm the 

 truth of the following observations, and agree with me in the de- 

 cided conviction I entertain of the superiority of wood over 

 iron. I feel fully justified indeed in saying that when the merits 

 of wood, and the demerits of iron are fully ascertained, the erro- 

 neous prejudice in favour of the latter, will cease to exist in the 

 minds of all candid men who are practically acquainted with the 

 properties of the two materials, Every person possessing even 

 a very small portion of knowledge of the expansion and contrac- 

 tion of all metallic substances, may foim some idea of the inevi- 

 table expansion of a large iron roofed house in a hot summer's 

 day, and of its unquestionable contraction during a night of severe 

 frost, so powerful have I known the action of the sun's rays to 

 prove in expanding the iron rafters and lights of a large roof on 

 a hot day, that I have found the strength of too and sometimes 

 three men required to force down the sliding lights for the ad- 

 mission of air. 



In fully equal proportion I have witnessed the contraction of 

 the metal during the intensity of the winter, when so large have 

 been the apertures between the rafters and the lights as to ad- 

 mit the external air, in a dergee sufficient to counteract entirely 

 the power of two strong fires when the flues have been heated to 

 the greatest excess before the temperature of the house could be 

 raised to three degrees of Franheit, the thermometer standing 

 at 18 degrees of frost, (out of doors) this was in February 1830. 

 Now this took place in a house of no very great dimensions 

 compared with the wood-roofed vinery I am about to describe. 

 The dimensions of this building were forty feet long by sixteen 

 wide, and nine high, with a pit in the middle for the culture of 

 pines, &c. which very much reduced the cubical number of feet 

 of air to be rarified as compared with the wood roofed house 



