On Penris Mode of Warming and Ventilating, 209 



number of roots, which of course procured additional nourish- 

 ment to the plant, and hence its larger size. The same may be 

 the case with trees and shrubs, which may have portions of their 

 fibrous roots disturbed by gusts of wind. 



The usual expedient for ventilating hot-houses, as it has been 

 called, is rather a misnomer; for, in fact, sliding lights were 

 and are employed more for reducing the temperature than for 

 admitting a current of air through the interior. Indeed, a cur- 

 rent of air, whether hot or cold, is ordered by some of our 

 preceptors to be provided against by interposing some kind of 

 open fabric over the openings ; and this is really sometimes ne- 

 cessary. But many practical men have long ago felt the incon- 

 venience of stagnant air in forcing-houses, which induced them 

 to try to dissipate it, by always opening both front and top sashes 

 at the same time ; or by setting both end doors open at once, in 

 order to produce a clear and strong current through the building. 

 For the same purpose, I have myself used what I called sijlap- 

 'per ; a thin panel of wood held between the hands, and flapped 

 forcibly downwards along the paths of the house, which dis- 

 lodged the lowest stagnant air. 



Mr. Weeks, senior, of the King's Road, Chelsea, who has 

 done, and is doing, so much in building and heating houses by 

 hot water, and who unites a knowledge of general gardening 

 with very considerable abilities as a mechanic and engineer, has 

 a vinery on his premises in which he invariably produces splendid 

 crops of grapes. Two or thi-ee years ago, he noticed that part 

 of his crop suffered from the want of ventilation, and, knowing 

 how rapidly hot air ascends, made, or rather inserted, a row of 

 three-inch pipes in the front wall, the outer ends flush with the 

 face of the wall, with stoppers to be used occasionally. The 

 inner ends of the pipes are brought close to the front hot-water 

 pipe, so that there is a constant blast of cold air impinging upon 

 the hot pipe, and from that to the top of the house, escaping 

 there through sliding shutters, which are shut or opened according 

 to the state of the weather. This arrangement qualified the heat 

 at the bottom of the trellis, and served to increase its ascent to 

 the top; and, at any rate, the vines grew and bore beautifully. 



It appears that heated air can be made to descend against its 

 natural tendency, by first withdrawing the colder and heavier 

 air from the lower part of the house: but whether a current of 

 air be impelled upon plants from above or from below can make, 

 I think, but little difference to the health of such as are shrubby ; 

 but, for pines plunged or set on a bed, a descending current is 

 most to be preferred, merely for its penetrating so much more 

 freely among the leaves, and reaching every part exposed to the 

 light. 



P 2 



