This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
In making the above remarks, I do not wish it to be understood that fresh air or copious ventilation is invariably an evil; far from it. Without a pure atmosphere no plant will flourish for any length of time: neither will fruit be of good quality, or flowers highly colored, or odorous; but I would caution all fruit and flower-growers against accepting the too common method of admitting bottom drafts, without a due consideration of the state of the external atmosphere, and also the stage of growth of the inmates. All that is needed in this respect is a suitable temperature and atmosphere, with abundance of light and a freedom from any noxious gases.
A few observations of a more mechanical character may be of service. We have seen, so far, that heat may be diffused through the whole cube of a house, but the tendency is to pass upwards, and out of the upper part of the roof; consequently there is a circulation of air in the interior, in proportion according to the influences at work. This, however, is not always in a direct perpendicular line, and even a cool bottom current may be produced without the aid of any ventilation. If we choose the common flue as an illustration, and consider it as placed on the ground level along the extreme front, the end nearest to the fire will be the hottest, and of course the radiated heat greater. In this case the opposite end close to the ground, at the back, will be the coldest and heaviest, and the air will move along the floor in a diverging diagonal stream, to take the place of that which is more rarified, the which will also travel in a contrary direction near the top. It will thus be seen that one part of a house so heated will be comparatively cold, while the other is warm.
If hot-water pipes are laid in the same position, with one flow and one return, the warmth at both ends of the house is equalized, the curreat being direct with the plane of the roof, and the coldest part will be, in less extreme, along the ground level at the back. In both examples there is a disparity of temperature; but if in the former the flue were continued in return a short distance from the back, the heat would be more generally diffused through the whole atmosphere, and in the latter nearly equal in all parts, while a constant circulation is kept up by the draw from the outside.
There have been many mechanical contrivances introduced for ventilating glass-houses, intended to supersede the common lift-up, let-down, or sliding sash, all of which are more expensive than useful. The main principle involved in such inventions is, the opportunity for admitting air from a chamber above the roof, and also warming it before entering the house in front. The known necessity for such appliances goes to prove the evil of cold drafts, but there is no reason why they should be let into a house, if the ordinary ventilators are attended to in a sensible manner; consequently such machinery can be dispensed with. True, if no attention is given to the way in which the admission of air is performed, much injury may be, and often is done, and many of the complaints of shrivelled leaves, stagnation of growth, mildew, and other bad effects, have their origin in this cause. The object of ventilation ought always to be the maintaining a suitable temperature and atmosphere within, while sudden differences are avoided.
If a house should happen to become too hot, it is not advisable to immediately throw open all the ventilators, even though otherwise such might be suitable, but to do so by degrees; because by such course the heat would pass off so rapidly as to produce a temporary vacuity, and an intense reduction of temperature, the which would condense the moisture previously in solution with the atmosphere, rendering it cold and dry immediately surrounding all surfaces of the plants that shortly before were being stimulated by opposite influences. Un- der such circumstances the juices undergoing assimilation in the leaves are drawn out, a violently paralyzing effect is produced through the whole structure, a possibility of permanently reducing the vital energy, and the accompanying proneness to disease and premature death.
It is requisite also to keep, as near as possible, an equal temperature over all parts of a house when the ventilators are open, the which needs some caution. The wind may blow in a diagonal line over the roof, or it may pass longitudinally. In either case, if the openings are equal in extent on the whole length, a strong current will enter the inside at the opposite end, and a rolling, as it were, of a cold volume down to and along the lower base; and the warm air will be rapidly expelled at the windward point of the upper openings. Such being the case, it is best to reduce the openings, or keep closed, according to circumstances, at the leeward end, and thereby prevent the evil. Again, the wind may strike directly across the roof, which will require all the openings to be alike, but care is necessary here that it is not allowed to enter so as to produce a cold and chilling effect.
There are many other details of similar character to what is recorded, which only require a trifling observation in the operator, consequently they need not be mentioned; and I hope these few remarks may be of service to the amateur, for whose benefit they are penned.
[Mr. Chorlton has here touched upon a most important subject, and one but little understood. His article is too long for comment, but we can not let the occasion go by without endorsing the general principle here set forth. The extract from Knight is specially to the point, and contains good sound doctrine, which addresses itself with peculiar force to the good sense of the intelligent grower. - Ed].
Mr. Chorlton has not yet, it appears, seen fit to change his views upon this subject, and advocates his favorite theory with much vigor and considerable ingenuity. I have no intention of arguing the point with Mr. C, for I have not forgotten the sever-ity with which he " came down upon" a correspondent of your journal last year, who happened to entertain different opinions, and I fear that I might find myself in the same category; I have nevertheless a statement to make, which I conceive rather militates against this air-tight plan of grape-growing. In my vinery - a small lean-to - the upper ventilators are placed in the back wall, and perhaps two feet below the roof, it being impossible, from the arrangement of the building, to place them higher; consequently there is above the openings a stratum of warm, moist, and stagnant air, into which the upper extremities of the vines have for two seasons been immersed. The point where the circulation of air ceases is quite distinctly marked, the vines below that point being strong, healthy, and fruitful, the foliage fine, and the bunches of good size, while above it the shoots are weak, the leaves small, and the fruit does not set.
When in pruning the vines I chance to thrust my head into this stratum of stagnant air, the sensation is extremely oppressive and almost suffocating, and this while both lower and upper ventilators are open, and the lower portion of the house quite comfortable. I am convinced that I must contrive a ventilator in the roof, or abandon the idea of obtaining any fruit upon the upper extremities of the vines.