BOOK III. 



FORMS OF HOT-HOUSE ROOFS. 



315 



that, in regard to form, the strength and tenacity of the iron bar, and the proper choice 

 of shape in the panes of glass, admits of every conceivable variety of glazed surface. 

 In this we have eomplctely succeeded, without in the least interfering with the objects 

 of culture. To render all these improvements available by the public, as matters of trade, 

 we transferred, in 1818, our right in the invention of the bar to efficient tradesmen ( W. and 

 D. Bailey, 272. Holborn, London), who have since, from our plans, constructed in a most 

 excellent style of workmanship, the curvilinear houses in different parts of the country, 

 of which we have already given a list and description. (1587.) 



1603. Some forms of hot-houses on the curvilinear prindpk shall now be submitted, and 

 afterwards. some specimens of the forms in common use ; for common forms, it is to be 

 observed, are not recommended to be laid aside in cases where ordinary objects are to be 

 attained in the easiest manner ; and they are, besides the forms of roofs, the most con- 

 venient for pits, frames, and glass tents, as already exemplified in treating of these struc- 

 tures. 



1604. The acuminated semi-globe. 



(Jig. 254.) The most perfect form ^-tssssrr^ 254 



of a hot-house is indisputably that of 

 a glazed semi -globe. Here plants, as 

 far as respects light, would be nearly 

 in the same situation as if in the open 

 air; and art, as already observed, 

 ( 1 592. ) can add heat, and all the other 

 agents of vegetation, nearly to perfec- 

 tion. But in respect to excluding the 

 rain, the semi-globe is too flat at top, 

 and requires to be acuminated ; and in regard to economy, the first cost and expense of 

 maintaining an artificial heat against its constant abduction through a thin medium, ex- 

 posed to the north winds, would, for most purposes, be a great objection. 



1 605. An acuminated semi-dome, or a vertical section of the last figure, placed against 

 a wall built in a direction from east to west, removes a great part of the objection as to 

 heat, and will still admit an adequate supply of light to plants kept constantly in the 

 same position, or turned very frequently. This, therefore, may be reckoned the second 

 best form for a plant-habitation for general purposes, and without reference to particular 

 modes of culture. 



1606. The semi-ellipse (Jig. 255.) is a figure which, in the plan (a, a), displays half an 



255 



