By Thomas Andrew Knight, Esq. 353 



provided that a considerable quantity, not less than twenty 

 tons, had been wanted. If the bars be made of the strength 

 proposed in the annexed sketch, each foot will contain twenty 

 ounces of iron, and each foot of the plates, which are to receive 

 the ends of the bars, about forty ounces ; in which case the 

 aggregate weight of the iron requisite for a forcing-house of 

 forty feet long, in the construction of which no timber what- 

 ever is used, cannot amount to half a ton, inclusive of all that 

 will be wanted to form cramps for securing the iron frame to 

 the brick work. 



Relatively to the expense of fitting and erecting the iron 

 work, I am not prepared to speak with any degree of accu- 

 racy ; but it cannot be very considerable : and as the curva- 

 ture of the bars will be every where the same, no difficulty 

 can occur in the application of them. It is, I think, not im- 

 probable, that iron bars of less weight that those proposed, 

 would be found sufficiently strong, particularly if metal of the 

 best quality were employed ; and such is Mr. Loudon's opi- 

 nion, to whose practical akill and extensive observation much 

 attention is due. 



