own garden in the Isle of Man, and has one in constant use for regulating the temperature of his apartments at his present residence'. This machine has been shown to Sir Joseph Banks, who thinks it will answer the purposed end; and I need not inform my reader of the value of the opinion of one so eminently qualified to judge, and whose extensive observation and experience have enabled him to augur of new inventions with such certainty that, as Sir Humphry Davy has remarked, it may be considered in him a sort of intuitive faculty?.

The importance of tradesman-like workmanship, or sufficient EXECUTION, has been already noticed. The remarks to be submitted on this subject relate chiefly to those variations of construction which I purpose introducing in hothouses.

In the masonry of hothouses particular attention should be paid to the foundations. A very common cause of decay is rents and settlements in the front wall, which of course receives the greater weight and thrust of the roof. The foundations of these walls ought to be deeper than usual, because the ground is liable in the course of cultivation to be stirred two or three feet deep; and the wall does not generally rest on its whole base, but on piers at certain distances, in order to admit the spreading of the roots, &c. Where rafters or uprights are used, I should recommend a pier under each, fourteen inches square under ground, and above ground of smaller dimensions, according to the weight to be supported. Instead of an arch from pier to pier, it will, in all cases where air is to be admitted by openings in the front wall, be preferable to employ stone imposts, and also to have that part of the pier which is above ground of one stone nine or twelve inches square, according to circumstances: see PL. X. Figs. 1 and 2. The object of this arrangement is to increase the pasturage of the

1 No. 7, Providence Buildings, New Kent Road. As soon as the machines are ready for sale, one will be erected here for the inspection of my friends.

* In a Lecture at the Royal Institution, speaking of the tannin found in terra Japonica.

roots at a, a, and the opening for admitting air at b, b, Fig. 1; and by having the stones properly rabbeted, to render wooden frames for the shutters of these openings, or wall plates for the rafters or astragals to rest on, unnecessary. The exact form of the upper surface of the wall plate must depend on the sort of rafter or astragal to be fixed on it. In general it should be such as will deliver outwards into a light gutter suspended from the stone, all the water of condensation which may run down the rafters or astragals.

In regard to the sort of stone to be used, each district has its local facilities for that material; but where there is not a good stone near the spot, and water carriage is not far distant, I should recommend a stone which in point of durability and strength surpasses the Portland; and differs from it chiefly in having more sand in its composition, and being of a yellowish colour. This stone is to be had in great abundance from Colallo in Fifeshire, and may be worked there to any form, and laid down in London so as to come considerably cheaper than Portland stone'.

The doors and openings for ventilation in the other walls should also have their sills, cheeks and lintels, of stone, properly rabbeted, so as there may be no wood-work required but for the shutters or doors.

Where pavement is used, I should recommend, as preferable to any pavement I have seen, the Arbroath flag-stone. It may be had in very large masses, which is a great advantage; and is so little absorbent of moisture, that even when laid on damp ground it always appears dry and comfortable.

The wood-work of hothouses such as I recommend, where improve

It has been extensively used in the Penitentiary at Millbank, and various other places; and specimens may be seen at Mr. Stoddart's, Strand. The present proprietor of this invaluable quarry, Mr. F. Braidwood of Edinburgh, has not yet been able to make it sufficiently known; in doing which he of course experiences great opposition from the proprietors and advocates of Portland stone. Excellent specimens of this stone, and also of the Arbroath pavement, may be seen in the greenhouse erected here (Bayswater) already referred to.

L

ment is an object', will be very trifling, and consist chiefly of shutters to the openings for ventilation doors, and fittings up for the back sheds. Sometimes also the outer frames of iron sashes are proposed to be formed of wood. In all cases, to promote duration, the wood-work of hothouses should be first fitted together, then taken asunder and painted two or three times with boiling tar. When dry it should be finally put together, and then painted with Le Souff's "anticorrosion," which after twenty years experience has been found the most durable paint for hothouses2.

The metallic work requires particular care in the execution so as to prevent rust. I have already mentioned a necessary precaution for that purpose (p. 45), and may here add, that where cast iron is to be used as wall plating, or in masses to be inserted in the ground, in walls, or used as tanks or cisterns, the composition with which Mr. Dickenson (inventor of the iron buoys) coats his patent iron casks will be found a desirable addition.

As the weight of cast iron rafters, as hitherto adopted in hothouses, has been an objection to their use, I shall here give some forms which will render them nearly or entirely as light as wood, with all the advantages (and some additional ones) of the heavy rafters of which there are sections in PL. VIII. Fig. 7.

1. Supposing the rafter intended for a common sloping roof for two tiers of sashes, both to slide, viz. the upper sashes to slide down, and the lower ones to slide up or down at pleasure; then Fig. 1, PL. IX. will represent a side view of such a rafter as cast, and before it has received the requisite fittings up. It may either be cast in one length, to be screwed together at a, a, or in four lengths, and joined at b,a,b. Fig. 2 is a side view of the same rafter fitted with rollers, d, d,

1 It sometimes happens that an architect in his employer's instructions is forbid to introduce any plan not in use in the neighbourhood, or which does not correspond with a house already erected, &c. &c.; in which case, plans in general use must be resorted to.

A very good proof of this may be seen in Miller and Sweet's Nursery, Bristol, and in some very neat wooden houses which they have erected at an adjoining villa.

which turn on fixed axles for the sashes to rest on instead of the usual rabbet, and which serve at the same time to lessen the friction when the sashes are in motion. The short cylindrical pieces, c, c, are cast apart, with gudgeons to fit small sockets, which sockets, with the cylinders fitted in, are screwed to the upper and lower bars of the rafter. The use of these vertical cylinders is to lessen the friction on the sides of the sashes when they are in motion.

Fig. 3 is a view of the same rafter completely fitted up, and with the sashes in their places.

e..f is a gutter suspended from the under edge of the rafter, to

h.

collect any water which may enter in the interstices between the sashes and rafter. This gutter may be formed of tinned iron, leather, or varnished papier maché; and as it rests on the forked ends of the wire suspenders, g, may be taken out and put in at pleasure.

it

Transverse rods to retain the rafters on edge and at equal distances, and also to keep down the sashes.

Supposing this rafter to be twenty feet in length, and the bars at an average three quarters of an inch square, it will weigh one hundred and three quarters, which at the present London prices will cost, including the fittings up, about 21. 10s. With regard to the strength of such a rafter, a sufficient number of experiments have not yet been made on cast iron to admit of a correct estimate; but there can be no doubt of its supporting ten hundred weight, or double the weight of the sashes which would bear on it, even if laid in a horizontal position and unaided by supports at any part between the two ends. By doubling the number of braces its strength will be increased by nearly one third part, and by placing it in an inclined position, like the sloping roof of a hothouse, every one knows that the weight it will bear increases as the cosine of the angle of elevation diminishes. The lightest wooden rafter that could be made to answer the same pur

'See Rees's Cyclopedia, art. Strength of Materials.

pose would require eight cubic feet of timber, which with labour at the present London prices would amount to 21. 88., to which must be added the expense of the rollers which would in this case be required for the sashes, the greater first cost of painting, and greater cost annually for repairs. The cast iron rafter would thus be the cheapest at first, the most durable, the most elegant, and it would not throw above one third of the shadow of the other on the glass.

2. Supposing the width of the house the same, and that it were (as in most cases it is) desirable that the one sash should move up, and the other down; then Fig. 4 will represent a side view of such a rafter with the sashes in their places.

a. An iron plate, which projects from the bottom rail of the upper sash over the upper rail of the lower sash, to carry

off the wet.

b. A projecting plate, for the same purpose, to throw off the water at the upper angle of the back wall.

c. Transverse rods to fix the rafters and retain the sashes. When it is desirable to open them further, they can be lifted up and tilted, or taken entirely off. This rafter would be equally strong, and one fourth cheaper than the other. Mr. Timmins' proposes a very neat mode of forming metallic rafters, by casing plates of cast or wrought iron with thin copper, which, if it were desirable to continue the old form of rafters, might in many cases be adopted with advantage, the precaution of tinning the copper being duly attended to before introduced in houses where grapes were grown. But curved rafters and convex roof promise so many

1 Specification of Patent for improvements in hothouses, March 1813. A very elegant house by Mr. Timmins is erected in Mr. Loddige's Nursery, which in point of lightness and tradesman-like workmanship surpasses any I have seen. Mr. Timmins generally tins his copper. Mr. Jorden, in his patent house erected for public inspection in the Union Nursery, King's Road, has used a light rafter; but as only a small part of the roof of that house is move able, it became an easy matter to omit superfluous strength. The water escape bars and grooves. in that house are neat and ingenious.