102 MATERIALS OF CONSTRUCTION. 



spirit, however, which has long held undisputed sovereignty 

 over the minds of gardeners, is fast giving way before the sweep- 

 ing current of mechanical inventions ; and when science comes 

 to the aid of mechanism in the building of hot-houses, as in the 

 erection of factories, steam-engines, and other works of art, then 

 the flimsy barriers reared by prejudice will be swept away, and 

 I think I may fearlessly assert that, in regard to the opposition 

 that has been given to the erection of iron hot-houses, this has 

 nearly taken place. 



Gardeners, from the early ages of Abercrombie and Nicol, 

 have been prejudiced against metallic hot-houses, and, to our 

 knowledge, this prejudice is still entertained by some whose 

 learning and intelligence would encourage us to look for more 

 accurate judgment. 



The objections which have been raised against metallic houses 

 for horticultural purposes, are chiefly the following : — 



Contraction and expansion, oxydation, abduction of heat, at- 

 traction of electricity, and original cost. 



In regard to the first, and principal cause of opposition, viz., 

 its susceptibility to the influences of heat and cold, a fact which 

 cannot be denied, yet it is proved by experience that if a house 

 be properly constructed of good material, this susceptibility is 

 of no practical importance. In very small houses the incon- 

 venience occasioned by sudden fluctuations of temperature may 

 be more sensibly felt, although, in the management of small iron 

 vineries, in England, we have never seen the slightest incon- 

 venience result from external changes ; indeed, all our expe- 

 rience in the management of hot-houses goes to prove the 

 superiority of iron over wood, for every purpose to which timber 

 is generally applied. It has been stated that metallic roofs are 

 more liable to break the glass than wood ; practice has also 

 proved that this statement is without foundation, and if it has 

 ever taken place, can only be in copper or compound metallic 

 roofs. Cast-iron or solid wrousfht-iron bars have never been 

 known to cause breakage of glass, or displacement of joints, and 

 some have asserted that the breakajre of <r\ass is even more 

 during sudden changes, by wood than by iron roofs. 



The expansibility of copper being greater than that of iron. 



