318 SCIENCE OF GARDENING. Part II. 



1612. A range of hot-houses (Jig. 202.) of any or of all the different varieties of cur- 

 vilinear surfaces, every one will allow to have a better effect than the common glazed 

 sheds or lean-to hot-houses of kitchen-gardens. 



262 



1613. Lean-to glass roofs are of various sorts. The simplest and most economical hot- 

 house of this description may be compared to a large pit. The back and front walls and 

 ends being of masonry, and a sloping side above of glass, and either fixed or moveable ; 

 if fixed, then air is admitted by openings in the front wall and top of the back wall ; if 

 moveable, the sashes slide, or are moved in grooves, the lower one being drawn up, and 

 the upper sash let down. Such a house will succeed perfectly well for grapes and pines. 

 The first improvement on this form consists in forming moving glass frames in front, in- 

 stead of the opaque wall of masonry and shutters ; a second consists in adding glass ends ; 

 a third, in forming the roof into two slopes ; and a fourth, in bevelling the positions of 

 the front sashes, and forming the whole roof into three different slopes, the lower for 

 receiving the sun's rays in winter ; the second for spring and autumn ; and the third, for 

 midsummer. 



1614. A variety of other forms will afterwards be given, both regular and anomalous, 

 adapted to specific purposes of culture, particular situations, as conservatories or cabinet 

 appendages to mansions, or for variety in flower-gardens. 



Scbsect. 3. Details of the Construction of Roofs, or the glazed Part of Hot-houses. 



1615. The glazed tegument, or cover, may either be wholly fixed, wholly moveable, or 

 partake of both modes. Each of these varieties may be considered in respect to com- 

 ponent parts and materials. 



1616. Fixed roofs are either formed of a series of bars "of iron or; wood, proceeding 

 at once from the front parapet to the back wall ; or from the base to the centre, or they 

 may be composed of sashes placed beside each other, or between rafters, as in common 

 lean-to houses. Roofs of this fixed kind have been approved of by Knight for vines ; 

 by Beattie, of Scone, for peaches ; and by most cultivators for the culture of pines and 

 palms ; but, excepting for the two latter purposes, the general experience of gardeners is 

 (in our opinion, very justly,) against them. -It is to be observed, that in all cases of fixed 

 roofs, shutters for ventilation are formed in the parapet, and in the upper part of the back 

 wall immediately under the roof. Economy in first cost, and less breakage of glass after- 

 wards, are the chief arguments in their favor ; the latter advantage, however, is generally 

 denied, it being improper glazing rather than the moving of the sashes, which occasions 

 the breakage of glass. 



1617. Moveable roofs are generally composed of sashes, six or eight feet 263 

 long, and three or four feet wide, which slide over each other, and are 

 moved by cords and pulleys, and sometimes balanced by weights, to 

 facilitate their motion ; but they are also occasionally formed of sashes 

 which open outwards by means of iron levers at their lower extremities, 

 and hinges at their upper angles (Jig. 263.), in the manner of the poly- 

 prosopic house. (Jig. 261.) 



1618. Roofs jwtaking of both characters generally have a few sashes 

 which let down or rise up in the roof or front glass ; or in the 



case of domes or acuminated roofs, the top part rises in the manner of a sky-light. 



1619. The material of fixed roofs is generally iron, as being least bulky in proportion 

 to the strength required, most durable, and admitting, in the case of curvilinear roofs, a 

 curvature to be formed at less expense than it could be of timber. In these roofs, in gene- 

 ral, no other bars or opaque bearers are required than those for receiving the glass ; and 

 hence their simplicity and unity with regard to component parts, and the equal degree of 

 transparency in every part of the surface. 



1620. The materials of moveable roofs are most commonly timber ; but frequently also 

 timber and iron, or timber and copper joined together. Thus cast-iron and wrought-iron 

 rafters are frequently used ; and in these are placed sashes with styles and rails of timber, 

 and bars of copper, and of cast or wrought iron. Two of the lightest-roofed shed-houses 

 yet built with sliding sashes are, one by Timmins, of Birmingham, in 1811, at Loddiges' 

 nursery, in which the rafters are of wrought-iron, cased in copper, to which are screwed 

 pulleys, on which the sashes, composed of copper bars and timber styles, slide without 

 grooves ; and the other is at the Union Nursery, King's Road, erected by J. S. Jorden, 

 in 1815, in which the upper part of the roof only moves ; the rafters are trusses of 

 wrought-iron, supporting bars of cast-iron ; and the entire sash is formed of hollow sheet- 



