STEAM. 319 



of an oblong form, furnished T\-itli safety-valves, and 

 heated by a smoke-consummg furnace. As in the com- 

 mon steam-engine^ the boiler is supplied from a cistern 

 above, and is made to regulate itself by a simple con- 

 trivance. In the feed-hfiad is a valve, which is opened 

 by the sinking of a float, which descends in proportion 

 as the water is dissipated in steam ; and, being balanced 

 by a weight, whenever a sufficient quantity of water is 

 admitted, rises again, and shuts the valv-e. As steam 

 may be conveyed, without materially impairing its calo- 

 rific powers, to the distance of several thousand feet, 

 one boiler is sufficient for heating all the glazed houses 

 which are ever erected together ; but a second is gene- 

 rally kept in readiness, to act as an auxiliary in case of 

 accident, or in very severe weather. Steam is con- 

 ducted from the boiler in a single main pipe, or in two 

 parallel pipes, which, according to Mr. Tredgold, may 

 be only one inch in bore. The divarications of the 

 pipes into particular houses are arranged somewhat in 

 the manner of flues, and, indeed, are sometimes placed 

 within these, or on them, when they already exist. 

 These interior pipes are from three to six inches in dia- 

 meter, in order to afford a greater radiating surface, 

 and are supplied with sets of valves, to admit, regulate, 

 or exclude the heated vapor, according to circum- 

 stances. 



The mos| perfect and extensive samples of steam ap- 

 paratus exiist at Syon House, the princely seat of the 

 Duke of Northumberland, near Brentford, and in the 

 nursery garden of Messrs. Loddiges at Hackney. At 

 the latter place, glazed houses, to the extent of almost 

 a thousand feet in length, and forming three sides of a 

 square, are heated solely by steam from one boiler. 



