521 



THE TRACTTCAL GARDENER 



In one conservatory, Mr. Horner has adopted an ingenious 

 plan of combinini^ strength and hghtness in the rafters. The 

 roof is of an cHiptical form, and the sashes are fixed. The 

 rafters are composed of one bar of wrought iron, three quartern 

 of an incli thick, and three inches broad ; this bar of iron if 

 covered with deal timber half an inch thick, and secured to tlu 

 iron bar with neat screw-bolts, so that they have the appear 

 ance of being wholly of wood, and their size is consequentb 

 only one inch and three-quarters thick, and four inches deep 

 which has a very light and neat appearance, while it is suffi- 

 ciently strong to carry the weight of the roof. If strength and 

 lightness be really indispensable for hot-house rafters, this 

 appears to be the princi[)le by which it can be eflected, as by 

 being covered with wood, all the conducting powers of heat, 

 cold, or electricity are corrected, and the eftbcts of contraction 

 or expansion lessened, so as to be attended with no bad conse- 

 quence ; and it is probable that rafters so constructed, will be 

 more durable than metallic ones, exposed to the action of the 

 weather. However, the expense of such rafters is considerably 

 more than wooden ones of equally proportionable strength. 



The rafters of the ix?ach-house in the garden of the Horti- 

 cultural Society are also strengthened, by having bars of iron 

 introduced into them, in a similar way, as are the rafters in the 

 conservatory of Mr, Hope, at Deepden; both houses are de- 

 signed by William Atkinson, Esq., and in both of them the 

 rafters are neat, light, and of suflicient strength to suj)port any 

 weight ever likely to be api)licd to them. 



Metallic houses attract electricity, and to guard against this 

 evil, it has been reconmiended to cover with thick coats ol 

 paint. Most painters consider that paint put on in thick bodies 

 defeats the i)urpose for which it is intended, by not adhering 

 so closely to the body on which it is placed, as thinner coats 

 of the same material, and, instead of protecting the body of 

 the material, is constantly peeling off. Putty is also recom- 

 mended to be spread over half the bar, to lessen the conduct- 

 ing principle ; most glaziers agree that the smaller the quan- 

 tity of putty used, the less liable it is to loosen or fall off; and 

 this is accounted for upon nearly the same principle, that thin 

 coats of paint are better than thick ones. There is certainly 



