104 MATERIALS OF CONSTRUCTION. 



same." From inquiries and calculations which we have made, 

 we have come to the same conclusion, although, from a want 

 of the requisite knowledge, and from the expense of having 

 patterns made for the castings, it may, in some localities, cost 

 more than a structure of wood. 



In small houses, sudden changes of the external temperature 

 are much sooner and more sensibly felt than in large structures, 

 whether they are constructed of wood or iron, which arises from 

 the fact that the smaller volume of air confined within becomes 

 more rapidly heated, and hence the change is the sooner felt. 

 Supposing the circumstance to be more strikingly sensible in the 

 case of small iron houses, then all that is necessary to coun- 

 terbalance it, is just a little more attention to ventilation, during 

 sudden changes of external temperature. 



For large structures iron is incomparably superior to wood, 

 and even for forcing-houses we would decidedly prefer the same 

 material. The contraction and expansion of metallic hot-houses 

 may be dreaded in the Southern States, if built on a very small 

 scale, and badly managed ; but in structures of moderate size, 

 this evil will be found practically of little importance, unless 

 they are badly constructed, and negligently managed. 



The finest horticultural structures that have yet been erected 

 in Europe are made of iron, and no houses of any importance 

 are now being erected of wood, which proves its superiority over 

 the latter material. The great conservatory, or Palm-house, 

 at Kew, is wholly of iron, constructed under the auspices of the 

 most scientific men in England. The Botanic Society's conser- 

 vatory, in the Regent's Park, (already spoken of,) is made of 

 iron. The fine plant-houses in the Glasnevin Botanic Garden, 

 near Dublin, are constructed of iron, and the quite unequalled 

 range of forcing-houses at Frogmore, in Windsor Park, are also 

 of iron. In fact, the most extensive horticultural erections in 

 Europe are made of iron, and many others, now in course of 

 erection, are being made of the same material. 



Admitting that properly constructed iron houses would cost, 

 at the outset, somewhat more than w r ooden ones, their lightness 

 and elegance render them much superior in point of appearance, 

 and, when their durability is taken into consideration, they will, 



