ON THE MERITS OF IRON AND WOOD FOR ROOFS. 53 



and to prevent drip in the house, which is highly injurious to 

 plants, particularly those grown in pots. 



Secondly, to form the roof in the following manner, the rafters 

 to be of wood varying according to the length of the rafter from 

 six to eleven inches, the section of the rafter to be wedge-shap- 

 ed from three to four inches wide on the upper side where the 

 lights rest, and half an inch wide on the bottom or under the ends 

 and sides of the lights to be made of wood, the top from five to 

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

 six to seven inches wide, and the sash bars to prevent as much as 

 possible the obstruction of the sun's rays, should be of copper, 

 which will give the house a light and neat appearance, without 

 subjecting the plants to the injurious extremes of temperature, 

 heat and cold, as the small quantity of metal in the thin sash 

 bars which need not be more than half an inch wide, and about 

 the same in depth, will cause but very little variation in the tem- 

 perature by radiation, aad little from expansion and contraction, 

 neither would it increase the expense of the light, but little more 

 than if made of wood, For as copper of that dimension would not 

 weigh more than 8 ounces to the running foot I should suppose 

 it would be bought for about eightpence per pound, therefore 

 the expence would be but triffling when compared with the ad- 

 vantage, indeed the extra expense would be gained in a few years 

 by the saving of wood in repairing the glass, as glazier's cannot 

 hack out old putty without destroying the sash bars, and this be- 

 ing very frequently repeated, as (is necessary when lights are kept 

 constantly in use) very soon lessens the substance of the sash 

 bars, I therefore recommend all persons when erecting forcing and 

 other houses, to have them constructed of the above materials, 

 particularly if they are desirous of excelling in the culture of 

 fruits and plants, as by the use of copper sash bars, they obtain 

 all the desired objects, viz. lightness of appearance, economy of 

 fuel, glass and labour. Moreover, any Gentleman before erect- 

 ing or deciding on any particular plan or dimensions of houses 

 for horticultural purposes, should consult his own gardener or 

 some other practical man, acquainted with the subject, as it is 

 impossible for any architect or surveyor to know the proper di- 

 mensions and elevations of hothouses, greenhouses, or other 

 erections, to ensure all the intended purposes, to which they 

 are appropriated so well as the gardener. It is true that an 

 architect may make a very interesting external drawing which 



