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lities which we now possess of protecting sloping walls, and coupled with the information communicated by Dr. Wells', may give rise to real improvements.

LAURENCE, BRADLEY, LONDON and WISE, SWITZER and others, have noticed the improvement proposed by M. Facio: but MILLER is the first practical gardener who avowedly treated of the subjects both of inclined walls and sloping glass, with a view to their application to horticultural architecture. He mentions the author of "Fruit Walls inclined, &c." as having "shown by calculation that there will be a much greater number of the sun's rays fall on a wall inclined to the horizon, than on one perpendicular to it;" and of having "taken the trouble of calculating the different inclinations which such walls should have in the different climates, in order to receive the greatest number of the sun's rays." Miller, as is justly remarked by the author of the excellent historical introduction to the " London Fruit Gardener," was too apt to condemn his contemporaries, and does not treat Facio with the respect to which he is justly entitled. He condemns the plan with but little argument: and as he was at that time considered in England as the arbiter olitorum et hortulanorum, and on the continent as omnibus in hac arte palmam præripienso, it will readily be conceived that his ipse dixit would be sufficient to prevent inclined walls from being tried experimentally. As far as I have been able to ascertain, they were only attempted at Belvoir Castle under Facio's directions. There they were unfortunately built on banks of earth, and found accordingly to be damp, thereby affording Miller a local argument against them, which has been repeated as a funda

Essay on Dew, 1814.

Fruit Garden Kalendar, 1718. Introduction, pp. 13 and 22.

New Improvements in Gardening, art. "Stove:" and in various works by this author from

1700 to 1724.

• London Fruit Gardener, chapter on Walls.

• Practical Fruit Gardener, art. Wall.

• Amænitates Academicæ, tom. iv. 213.

mental one by almost every writer who has touched on the subject, from his time to the present day; including the compiler of an able article on horticulture just published in the Edinburgh Encyclopedia'.

In the seventh and eighth editions of Miller's Dictionary (the last published in 1768) the articles STOVE, SUN, GREENHOUSE, and several others, are considerably enlarged by reflections and arguments on the slope of glass roofs; in all probability suggested by Facio, Boerhaave, and what the author had seen during his stay in Holland. Speaking of dry stoves, he says they may either be built with "upright and sloping glass" or "with the latter" only "placed at an angle of 45 degrees, the better to admit the rays of the sun in spring and autumn when the sun declines." This he says "has been the general prac

tice;" but he adds, "where I have had the contrivance of stoves of this kind I have always built them after the model of the bark stove (i. e. with upright and sloping glass); because this will the more easily admit the sun at all the different seasons; for in summer when the sun is high, the top glasses will admit the rays to shine almost all over the house, and in winter when the sun is low, the front glasses will admit his rays; whereas when the glasses are laid to any declivity in one direction, the rays of the sun will not fall directly thereon above a fortnight in autumn and about the same time in spring 2."

We are informed under the article SUN, that as the difference between the heat of summer and winter depends on the obliquity of the sun's rays, this should be well considered in the contrivance of stoves, which ought to have their glasses so situated, as to receive the sun's rays in direct lines, during as great a portion of the year as possible; "for which reason the stoves which have upright glasses in front, and sloping glasses over them, are justly preferred to any at present contrived."

It is proper to remark here, that forcing houses for grapes and

J Mr.P Niel, Secretary to the Caledonian Horticultural Society.
Miller's Dict. art. Stove.

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peaches were less in use in Miller's time, than greenhouses and botanic stoves; and that this author was more a botanical than a culinary gardener. Had the demand among the opulent for early and high-flavoured fruits been as great then as it is now, it is probable so intelligent a writer and general observer would have made a nicer distinction between houses for general purposes, or maintaining an artificial climate during the whole year; and such as are only intended to mature crops of fruit at particular seasons.

The importance of this distinction was reserved to be illustrated by Mr. KNIGHT; who has not only shown its use theoretically, but confirmed its utility by several years experience.

In one of the examples given by Mr. Knight, his object was to force a large and high-flavoured, rather than a very early crop of grapes; and he accordingly fixed upon such a slope, as that the sun's rays might be perpendicular to it in the beginning of July, the period about which he wished the crop to ripen. The slope of the roof to effect this purpose in lat. 52 he of course found to be 34 degrees. The house was forty feet long, with fixed sashes, no front glass, and to which air was admitted at the ends only. It produced, we are informed, "the most abundant crops of grapes perfectly ripened, within less time, and with less expenditure of fuel, than I have witnessed in any other instance'."

The second instance of Mr. Knight's application of this principle, is to a peach-house. The sloping glass of this house he placed on an angle of 28 degrees, that the sun's rays might be perpendicular to it before the ripening season; because (as peaches ripen with most flavour when exposed to the open air) Mr. K. removes the lights before midsummer. This house is fifty feet long, nine feet high, with no

1

Description of a Forcing-house for Grapes, with Observations on the best Method of constructing them for other Fruits.-London Hort. Trans. vol. i. p. 99.

I had an opportunity of seeing this vinery at Downton Castle, near Ludlow, in the year 1807, shortly after it was built.

C

front glass, but with the sloping glass moveable to admit air. This plan he recommends, as combining more advantages than can ever be obtained in a higher or wider house. He adds: “I estimate so highly the advantages of bringing forward the fruit under glass till it is nearly full grown, and then exposing it to the stronger stimulus of sunshine, without the intervention of the glass, and excluding it from air and dews, that I believe the peach might be thus ripened in greater perfection at St. Petersburg, in a house properly adapted to the latitude of that place, than in the open air at Rome or Naples." Hort. Trans. p. 206.

In addition to these experimental proofs of the excellency of the principle by Mr. Knight, we have a formula for its application, by the Rev. THOMAS WILKINSON'. He says: "having determined in what season we wish to have the most powerful effects from the sun, we may construct our houses accordingly, by the following rule. Make the angle contained between the back wall of the house and its roof= to the complement of the latitude of the place + the sun's declination, for that day on which we wish his rays to fall perpendicularly. From the vernal to the autumnal equinox the declination is to be added, and the contrary."

Mr. Wilkinson has added to his valuable scientific communication Bouguer's Table of rays reflected from glass, which, in connection with the above formula, is extremely useful, and serves to give a striking view of the disadvantages of obliquity to the sun's rays, whatever may be the nature of the surface on which he shines. From this table it appears, that if 1000 rays fall upon a surface of glass at an angle of 75°, 299 of these rays are reflected; consequently in little more than an hour after each mid-day, in spring and autumn, nearly one third of the effect of the sun is lost on all hothouses with parallelogram bases and common sloping roofs fronting the south, what

1 London Hort. Trans. vol. i. p. 161.
See Bouguer, Traité d'Optique.

ever may be their angle of inclination; and, that as the sun declines further from the meridian the loss is consequently proportionally great'.

Before I proceed further in tracing the progress of this principle, I beg leave to refer to the diagrams in PLATE I. which contains an elementary illustration of the whole subject, from 1699 to 1817.

Fig. 1. Is a section of an Orangery," according to the laws of Boerhaave:" it is nearly a fac simile of the diagrams given in the Encyclopédie Méthodique and the Amanitates Academica under this designation. I mention this, because at first sight it does not appear consistent with the quotation from the Elementa Chemiæ, given above, which directs the front glass to be placed at an angle of 14° 30′ "to the pavement." From the context and spirit of the passage, however, we must evidently understand an angle of 14° 30′ to the perpendicular. This diagram may be dated 1720.

Fig. 2. Is a section of the Caldarium or stove erected by Linnæus in the botanic garden at Upsal, in 1740, and referred to by him in his Descriptio Hortus Upsaliensis quoted above. It contains horizontal flues (camini horizontales) under the front glass and at the ends, for the purpose of heating the house; and in the centre, towards the back wall, an exposed fire-place, or Swedish stove, for drying the internal damps and dispelling exhalations when external air cannot be admitted.

'The formula for calculating the effects of the sun's rays on opaque surfaces will be found 'in Facio's work above mentioned, (page 38 et seq.) and also in an interesting paper in the Phil. Trans. by Dr. Halley, No. 203. The result is, that "the quantity of the sun's rays falling upon any plane, is as the sine of the sun's altitude upon that plane;" and that the force of each ray is governed by the same laws. Whence it follows, "that the whole action of his upon a plane is as the square of the sine of the sun's altitude on the plane and the time that action lasts jointly, neglecting the effects of the atmosphere." Coupling this formula with Bouguer's table of rays reflected from glass, it is evident the exact influence of the sun may be calculated on any description of surface, whether transparent or opaque, and however curved or inclined.

rays

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