FORCING DEPARTMENT. 321 



as sound as when first executed, although of but 

 very slight manufacture, in comparison to the bars 

 constructed in the present day. 



There are, also, in the Gardens here, cast iron raf- 

 ters, and wall-plates, that have now, for nearly 

 twenty years, been used in a couple of Pine pits, 

 still as sound as when first cast. The lights of these 

 pits are constructed of wood, and have been, for 

 several years past, constantly under the necessity of 

 having some part or other renewed : these are 

 heated with dung, and, also, with hot water; so that 

 either, or both heats, may be applied at pleasure. 

 The steam, arising from the fermenting substancer, 

 is very detrimental to the wood, whilst its pernicious 

 effects do not injure the metal in the slightest degres . 

 In short, I should recommend cast metal rafters, 

 and wall-plates, in all pits that are heated with 

 dung. 



Various other instances, in proof of the durability 

 of metallic roofs, might be referred to, from works 

 that were executed from thirty to forty years ago. 

 The numerous objections that have been raised 

 against metallic Hot-Houses, have been principally 

 advanced by those who never had them under their 

 own immediate charge, or by those who have had 

 the cast metal, or the sashes whose bars were com- 

 posed of the sheet iron, and enveloped in a thin bit 

 of copper. But, injustice to the public, the opponents 

 of the metallic roofs would but act fairly to state 

 the exact materials of which the houses that they cite 

 are constructed. 



Mr. M'Intosh, an excellent scientific and practical 

 2 T 



