44 STRUCTURES ADAPTED TO PARTICULAR PURPOSES. 



linear house, and should be made of iron, as a curvature for this 

 purpose can be made cheaper of iron than of wood, and is 

 tighter and more durable. Iron beams are made to screw into 

 the rafters, b, b, b, , having a fillet in which the smaller rafters 

 are placed, on which the sashes run. We have seen two methods 

 of constructing this kind of roof, the one just described, in 

 which the sashes are made to slide, and another, in which the 

 sashes are made to rise on hinges, by which the house may be 

 aired, over the whole surface of the roof, or entirely exposed, for 

 admission of a congenial shower of rain, or for hardening the 

 vines or peach trees, after the crop has been gathered. The 

 arrangement by which this is effected is exceedingly simple, not 

 liable to get out of repair, and is applicable to all kinds of houses, 

 whether the roof is formed of curved or straight lines. This 

 form of house is considered by Loudon as the ne plus ultra of 

 improvement, so far as air and light are concerned. We are of 

 opinion, however, that these considerations alone render it less 

 valuable in this country than it is in England, except, as we 

 have already stated, for the purposes of winter forcing. 



The Cambridge pit, Fig. 7, is admirably adapted for early 

 forcing, where there is an abundant supply of stable manure. 

 It is heated entirely with fermenting material, and is much used 

 in England for the purpose of growing pine-apples, melons, 

 cucumbers, &c. a, #, are shutters, which lift entirely off, or are 

 wrought up and down by hinges attached to the back wall of 

 the pit. These shutters are made to fit closely on the lining 

 bed, b } b, which is kept constantly filled with the materials to 

 supply the heat, which enters the interior of the pit through 

 pigeon-holes in the wall. We have kept pines during long and 

 severe winters, in this kind of pit, keeping up a temperature of 

 50 to 55 in the coldest weather. During winter the linings 

 require to be frequently renewed, at least every week some fresh 

 material must be added, otherwise the heat will decline below 

 the minimum temperature ; and, as it will be some time before 

 the new linings generate much heat, a part should only be re- 

 newed at one time, and never both sides of the pit at once. 



Saunders' forcing-pit, Fig. 8, is considered an improvement 



