Holland, Cape, Palm, Chinese, or Succulent tribes. On a large scale, they would admit of the growth of trees almost to their natural size; as for example, the Norfolk Island Pine, Musa, &c. in the centre, and smaller growths towards the circumference: and by a little judicious contrivance they might be constructed low at first, and raised according to the progress of the trees.

PLATE III. contains a section of a campanulated house, fifty feet high, intended for large trees in the centre, and smaller articles towards the circumference.

a. The flues, and pathway over.

b. Mode of opening the whole of the glass to admit at pleasure

air, wind, rain, and the direct influence of the sun.

c. Basement walls.

Fig. 1, PL. IV. is an elevation of an acuminated figure, intended as a small dry stove. The glass, excepting the acuminated part, is fixed; air being admitted by raising that part of the glass, and by opening the horizontal shutters in the basement wall.

Fig. 2. is a vertical section, in which the acuminated part is shown raised to admit air. Under the pavement of the circular walk is a can flue bedded in dry sand, as seen at a. Under the stage, b, b, which is a cone of steps, is a reservoir, c, into which the flue, after having made the circuit of the house, discharges itself; thus affording the smoke ample space to give out its caloric, before it escapes by the horizontal chimney, d. By casing each step with a thin circular band of plate iron, a cone of earth or bark might be formed, and thus a moist heat supplied; or a common circular bark pit might be substituted for the stage and reservoir, &c.

Fig. 3 is a plan, and Fig. 4 a dissected vertical profile, showing the arrangement of the astragals of the roof, and the walk, basement wall, entrance, &c. Elegance being a principal consideration in buildings of this sort, it is almost needless to mention that the fire-place, chimney-top, &c. should be properly concealed, which in general can be readily effected by bushes, or other local facilities.

In PLATE V. Fig. 1, a design is submitted, in which a part of the idea suggested by Adanson and Sir George Mackenzie is applied to what I would call a forcing-house for general purposes, as opposed to such as are calculated for particular seasons, and for ripening the whole crop at once, which takes place in common houses with inclined roofs, and may be very suitable for an immense establishment, but is not to be desired where there are perhaps but one or two houses for each department. To the idea of a semidome or curved roof I have added one of my own; and though I have not hitherto had an opportunity of executing it on a large scale, yet it is evidently well calculated to promote the influence of the sun on the trellis of every description of longitudinal house. I allude to what I call a ridge and furrow disposition of the glass, which is to be effected in two ways, viz. either by ridge and furrow glazing, or by ridge and furrow roofing.

In the first, instead of having the astragals of a sash in the same plane, they are placed in two planes alternately, raising one and depressing the other; so that, when glazed, the glass declines from the high or ridge astragal, to the low or furrow astragal. The cross section of a sash so glazed would be a zig-zag line, as in Fig. 1, PLATE VI.

Ridge and furrow roofing is merely effecting the same object on a larger scale, by raising and depressing the rafters alternately, as shown in the section Fig. 2, PLATE VI.

The object to be attained by this mode of glazing is two daily meridians; the one earlier, and the other later than the natural meridian, in proportion to the angle of elevation of the ridge astragals or rafters. In this way the sun's perpendicular influence is obtained an hour or two earlier, and retained an hour or two later, all over the house; an object which in longitudinal houses facing the south cannot be effected by any other means. This proposed improvement ap plies equally to front as to sloping glass, and whether the slope be rectilineal, or part of a circle, polygon, or other figure. Domes, and

houses whose plans are segments of circles or of ellipses, are those only to which it does not offer any, or but few advantages.

Imagine Fig. 1, PL. VI. to be a section of a sash glazed in the ridge and furrow manner; Fig. 2 a section of a common sash; and a, b, c, in both figures, the sun's course. Then, when the sun arrives at a, or eleven o'clock, in Fig. 1, he is perpendicular to one half of the glass of the sash; but when at a, Fig. 2, his rays form an angle of 72° with its surface; and the incidental angle being 20°, 25 rays in every 1000 are reflected. In like manner in the afternoon, when he arrives at one o'clock, the same advantages will result to Fig. 1, and the same disadvantages to Fig. 2; and this, whether the sashes are placed in an ́upright or in a sloping direction.

It is true there is a corresponding loss of 25° in 1000 when the sun is at b, or in the natural meridian: but as each ray, from being then at its greatest elevation, has its maximum of power, the loss sustained will be more than counterbalanced by the earlier and later meridians, which give a double chance of obtaining the sun's full influence in cloudy weather, and prolong his influence in clear weather.

There is another advantage of the ridge and furrow glazing shown in Fig. 1, which will be found of consequence in hotbeds, pits, and in all flat roofs of glass. When the declivity from the ridge astragal to the furrow astragal is greater than the slope of the roof, the internal dews will of course be thrown towards the furrow astragal. By forming a gutter, d, Fig. 1, on the under edge of the moulding of that astragal, these dews may be collected and carried off; and in this way, dropping, so much complained of by gardeners in early cucumber frames, and in most houses with a glazed lap or overlap, may be more effectually prevented than by any other mode hitherto devised. I have proved this in a greenhouse and pit erected here, in which one sash glazed in the ridge and furrow manner is placed in the same roof with six others glazed in as many different modes, and all at an angle of 11 degrees. As they are very flat, some drops fall from the whole of them; but invariably the smallest number from the ridge and furrow

sash, and in the proportion of one to five with the close puttied, or closed metallic lap.

Fig. 3 is a section of part of a ridge and furrow roof, which on inspection will be found to be merely a disposition of sashes, similarly to the disposition of panes in Fig. 1, and consequently that it produces the same effects. In this mode it is necessary that the slope of the roof be greater than the slope from the ridge rafter, d, to the furrow rafter, e, in order that neither the inside dews nor the rains externally may rest on the puttied rabbets of the astragals. Such a house as that of which PL. I. Fig. 6. is a section, would be rendered complete as the earliest description of forcing-house, by having its glasses disposed in this manner, and at such an angle as that the early meridian might take place at ten, and the late at two o'clock.

But to return to the design submitted in PL. V.-Here are no rafters; but a curved astragal, with the upper part straight, is used throughout, and only supported or steadied by two horizontal cross bars of the same thickness as the astragals. The ends are quarter domes, glazed as in the hemispherical house. The whole roof is fixed, air being admitted by the horizontal shutters in the front wall, and the windows at top and bottom of the back wall. The longitudinal part of the roof between the two ends, though presenting as a whole a convex surface, yet in detail is ribbed or glazed in the ridge and furrow manner just described. A canvass outer roofing is adapted to the glass. The results of this construction are

1. From the globular form of the longitudinal part as a whole, the sun will be perpendicular to some part of it every midday throughout the year.

2. From the ridge and furrow glazing of its detail, he will be perpendicular to half the entire roof twice in every day throughout the

year.

3. From the use of astragals without uprights, imposts, rafters, sashes, &c. &c. and from the circular.ends, the greatest possible quan

E

tity of transparent surface is obtained consistently with a moderate size of panes.

4. The canvass covering, by preserving a heated atmosphere outside the glass, will retain the heat within, prevent dews from condensing, or water-drops from forming on the glass, and lessen the consumption of fuel, as well as the risk from too great or too little heat during night.

Contrast this construction with any form hitherto devised;—with the common sloping roof, to which the sun cannot be perpendicular more than twice a year, and where a third of his rays are obstructed by rafters, sash-frames, &c.; with the globular house or semidome, where the trellis is too far from the glass; with the roof at an elevated angle, which loses great part of the sun's effects at midsummer; and with that at a depressed angle, which loses great part of his effects in midwinter;—and the advantages of this house will appear striking. That it will be less expensive in the erection, must be evident from the entire omission of rafters and moveable lights. The following detail will render this design more intelligible:

In Figs. 1, 2, and 3,

a. represents the foundation piers of the front wall.

b. Air valves, or shutters between each pier.

c. Coping of the front wall, showing a plan of the zig-zag or

ridge and furrow glazing.

d. The quarter dome ends and entrance doors.

e. Front trellis.

f. Trellis for temporary use, placed in the back part of the house,

h. Course of flue in back shed to temperate the air for the growth of mushrooms, and for ventilating the front house.

i. Windows for the purposes of ventilation and light to mush

room-house and sheds.