Transactions of the Horticultural Society. 



201 



are accurately fitted, (c). In the 

 back wall, within the house, and 

 next the glass at top, are also 

 fitted a corresponding number of 

 wooden frames (d), furnished with 

 a wooden slider, running up and 

 down by means of pullies with 

 cords and weights, after the man- 

 ner of a window sash, (e) These 

 sliders are interposed between 

 a hollow in the wall (/), which 

 communicates with the external 

 air in front, above the glass roof 

 of the house, (g) When it is 

 wished that no air shall be admit- 

 ted, the front shutters and the back 

 sliders are closed, and in propor- 

 tion as it is desired to ventilate the 

 house, are they opened to a greater 

 or less degree. By these means a current of air is maintained from front 

 to back ; and as fast as the admitted air becomes heated, and rises in the 

 house, it escapes through the ventilators at the top of the back wall. 

 When it is expedient to admit fresh air, without loss of much heat, the 

 front ventilators alone are opened. The ventilation of the houses being 

 thus effected with facility and accuracy, renders the moving the lights 

 for that purpose unnecessary ; and, in consequence, all the sashes in the 

 houses erected in the garden of the Society, excepting those of the peach- 

 houses, are now fixed. By aid of these ventilators, the temperature of 

 iron houses is capable of being lowered in the hottest days of summer to a 

 degree even inferior to that of the external air. The advantage in ob- 

 viating the wear of wood- work, and the breakage of glass is manifest." 



Humidity in the houses. Some observations, taken with 

 Mr. Daniel's hygrometer, have led to the conclusion, that 

 .860 of that instrument, the temperature being from 80° to 

 87°, and the transmission of light such as takes place through 

 a curvilineal roof of iron bars and crown glass, is the most 

 suitable to tropical vegetation. 



" It can also be stated, that unless such a degree of humidity is carefully 

 maintained during the summer months in a hot-house constituted of iron, 

 such a house will be found more rapidly prejudicial to the health of plants, 

 than one constructed of wood, because its atmosphere, if left to itself, 

 would become more dry, and the plants would exhibit all the symptoms 

 consequent on aridity." 



We have before observed (vol. i. p. 292.), that whatever be 

 the description of house, when the temperature is high, say 

 from 60° upwards, the gardener can never go wrong in regard 

 to atmospheric moisture, if he keep the floor well watered. 

 This being done, the heated air will always take up the 

 natural proportion of vapour. Mr. Daniel's hygrometer is 

 perhaps the most accurate instrument of the kind, but un- 

 fortunately for its coming into general use, before any thing 



