64 STRUCTURES ADAPTED TO PARTICULAR PURPOSES. 



given to hot-houses by taking different segments of a sphere, 

 I, however, soon became fully satisfied that forcing-houses, of 

 excellent forms for almost every purpose, and of any convenient 

 extent, might be constructed without deviating from the spheri- 

 cal form ; and I am now perfectly confident that such houses 

 will be erected and kept in repairs at less expense, will possess 

 the important advantage of admitting much more light, and will 

 be found much more durable, than such as are constructed 

 according to the methods and forms which have hitherto been 

 recommended." 



Fig. 21 is a representation of what is called the zig-zag, or 

 ridge-and-furrow roof, which has not, as far as we know, been 

 very extensively adopted. There are several places in Eng- 

 land where this method of roofing has been adopted, but prin- 

 cipally as an experiment, or merely as the fancy of the erector. 

 The advantage of this mode ,of roofing is, that the rays of the 

 sun are presented more perpendicularly to the glass in the 

 morning and afternoon, when they are weakest, and more 

 obliquely to the glass at noon, when they are strongest. We 

 doubt, however, though the arguments we have heard urged 

 in favor of this kind of houses be indisputable, whether the 

 additional expense required in their construction will be coun- 

 terbalanced by the advantages gained. There is no doubt the 

 expense of their erection militates very much against them ; and, 

 if they could be erected as cheap as plane roofs, they are decid- 

 edly superior to them for graperies, as the vine can be trained 

 up the middle of the ridge, and, consequently, though suffi- 

 ciently near the glass, the intense rays of the sun will be less 

 injurious than under a plane roof. 



The ridge-and-furrow roof may be carried out either on com- 

 mon plane-roofed houses, or on the curvilinear principle, though 

 doubtless the latter is more difficult of construction, and, of 

 course, more expensive ; but we have no doubt, if the principle 

 of constructing horticultural structures were fully understood by 

 competent manufacturers, who had directed their attention to 

 the details of the structures, that this, or, in fact, any other 

 form of structure, could be made as cheap as the houses now in 

 common use. 



