52 



FOSM OF GREEXHOU.^ES. 



cannot be obviated without deviating from the spherical to the spheroidal 

 form, which Sir George states to be objectionable, on account of the 

 great nicety required in the workmanship. On making a few trials to 

 ascertain the variety of forms wliich might be given for hot houses, by 

 taking the different segments of a sphere, I soon became perfectly 

 satisfied that forcing houses, of excellent form, for almost every purpose 

 and of any convenient extent, might be constructed without deviating 

 from the spherical form, and I am now," says he, " perfectly confident 

 that such house v>ill be erected and kept in repair at less expense, 

 \Yi\l possess the important advantage of admitting more light, and wiU. be 

 found much more durable than such as are constructed according to any 

 of the forms that have been hitherto recommended. By employing a 

 small segment of a large sphere, as low and as wide a forcing house as 

 can be wanted for any purpose, may be readily obtained. Instead of the 

 half, a hemisphere of thirty feet diameter, let the half of one of fifty be 

 chosen, and from the base of this cut off thirty five degrees, and fi'om the 

 summit fifteen degrees, and the following proportions for a forcing house 

 will be given. Its height, (including eighteen inches of upright, opaque 

 front, opening as shutters), will be twelve feet ; its ^vidth in the centre, 

 fourteen feet, and its length very nearly forty feet ; and there are few 

 purposes for wliich a house, constiTicted according to some of the inter- 

 mediate forms, between that above mentioned and the accuminated semi- 

 dome, will not be found extremely well adapted." 



Cunihnear-roofed hot houses of all shapes, we ought to observe, require 

 very great care in regulating the effects of solar heat, particularly those 

 that are constructed of metallic matter. From the experiments made in 

 the gardens of the London Hoiticultural Society, and pubhshed in the 



Transactions " of that Society, vol. YI. p. 379, we learn that in the 

 first year of its trial, the roof was permitted to be wholly exposed to the 

 action of the sun, but it was fomid impracticable to regulate its tem- 

 perature under such chcumstances, although the house was ventilated, not 

 only by means of apparatus in the front and back walls, but the two ends 

 of the house were so contrived that they will open almost enthely when 

 necessary, so that a current of air may be introduced both at the ends and 

 §ides. The temperature was indeed kept regular dming the night by 

 means of fire heat without difficulty, but in the day time it was found 

 impossible to do so. "WTien there were alternate changes from a clouded 

 to a bright sky, the action of the sun's rays was so sudden, that the 

 thermometer of the house was raised too high before the speediest supply 

 of air could be given ; and when there was a whole day of continued 



