ordinary circumstances, simple improvements, and such as when they go out of order can be readily repaired by local artists, should be adopted in preference to more perfect plans which require greater skill in the management, and more expert artisans to reinstate them in case of derangement.

HEAT is artificially communicated to hothouses by fire, steam, and the putrefactive fermentation of vegetable substances. Heating by fires is the most ancient and general mode. Originally in this country hot embers were placed in a hole in the floor. On the continent, fires were made in stoves erected within the house2; and subsequently they were kindled at one end of a large vault under the floor, the smoke going out by a chimney at the other3. To these plans succeeded horizontal flues1, reserve chambers of heated air, air flues, and the introduction of hot air through metallic tubes in contact with the fire7. OneWatts, gardener to the company of Apothecaries at Chelsea, in 1684, seems to have been the first to convey heat by tunnels underneath the floor of his greenhouse; and Evelyn', a few years after, gives a plan for introducing a constant supply of heated air from the fire-place, very similar to the mode for which a patent has been recently obtained by the Marquis de Chabannes. The various alterations and

'Ray's Letters, 172. This was originally the practice in private houses, and heuce the curfew or couvre feu, &c. See Beckmann's History of Inventions, vol. ii. p. 103.

• Parkinson's Herbal, p. 588. Niederlandische Hesperides, 145.

Ecole du Potager, Paris, 1750; and Kirchner's Praktische Anleitung für Gartenkunst, &c. Leipsig, 1796.

Linnæus in Descriptio Horti Upsaliensis. Maison rustique, 3ieme edit. art. Serre.

Encyclopédie Méthodique, art. Serre. Van Oosten in Dutch Gardener, 1711.

Dr. Anderson in Patent Hothouse, and in Recreations.

Evelyn in Kalendarium Hortense, App. to 4th edit. Gouger in Méchanique du Feu,

Paris, 1713, and La Maison rustique, p. 14, tom. ii. edit. 1768.

9

Explanation of a new Method for warming and purifying the Air in private Houses, &c. London, 1815. Gouger's work, translated and improved by Desaguliers in 1715, contains the rudiments of the Marquis de Chabannes, and almost every other modern improvement in toves and fire places.

improvements that have been made from Evelyn's time to the present day, are so numerous as not to admit even of recapitulation in these Remarks. Most of them may be found in the Repertory of Arts, and the principal French and English Encyclopedias, particularly that of - Dr. Rees. In as far as respects hothouses, the subject has been treated of in the most ingenious manner by Dr. Anderson; and Mons. Guyton in the Annales de Chimie has given the ablest view of its economy for domestic and general purposes.

The earliest proposal which I have met with for forwarding vegetation by steam is contained in the Gentleman's Magazine for January 1755; and the first who actually practised steam forcing appears to have been Mr. Wakefield of Liverpool in 1788. Mr. Hoyle of Halifax took out a patent for heating hothouses and other buildings by steam in 1791. Mr. Butler employed steam with success in a pinery at Knowlsby in Lancashire in 1792, and Mr. Green in dwelling-houses and greenhouses in London in 1793'. Mr. Mawer of Dalry near Edinburgh adopted steam in 17942 in three pineries, two peachhouses, and two vineries, and Mr. Weston of Leices ter, in pits about the same time. Subsequently Mr. Thomson at Tynningham3, Mr. Williams*, Dr. Lisle, Mr. Dennison, and various others, down to Mr. Fraser7, who at the Royal gardens at Kensington has recently commenced his operations for heating by steam more scientifically than (as far as I know) has hitherto been done. In all the above instances, excepting Hoyle's and Fraser's, the steam was admitted to mix with the air of the house, and condense on the plants;

'Repertory of Arts. Buchannan on Heating by Steam, p. 164.

• Robertson's View of the Agriculture of Mid Lothian, Appendix, Edinburgh, 1798.. The Earl of Haddington's seat near Dunbar.

London Hort. Trans. vol. i.

At St. Fagons near Cardiff.

At Dorking: steam is also employed in a hothouse at Clapham, and at Mr. Loddige's nursery, Hackney.

? Ironmonger and Brazier, Long Acre, London.

a mode which effectually destroys insects, and may therefore be occasionally resorted to; but which, considered merely as supplying artificial heat, is attended with the greatest uncertainty. The only work which has yet appeared on the subject of heating generally by steam, is that of the late able engineer Mr. Buchannan '.

Probably the most ancient mode of forcing is that by the use of fermenting vegetable substances. It is mentioned by Lord Bacon as a thing common in his time 2, and in L'Ecole Potagere by Combles, La Maison rustique, Quinteney, Bénard, and other old French authors on gardening and rural affairs, as long practised in their country for raising cucumbers and melons. Laurence is the first English author who proposes using dung to force his favourite fruit the grape; and from the time of this writer to the present day, it has been occasionally adopted on a limited scale for this and similar purposes, though from the limited supply it is not likely to come into general use, otherwise than for hotbeds or pits. Speechley and McPhail have best treated the subject of moist heat, as it is called, and the construction of dungpits and hotbeds.

Other modes of heating may be occasionally resorted to, such as from the waste hot water of a distillery or brewery, hot ashes from a foundry, hot springs, &c. as at Matlock and Toeplitz, where hothouses might be thus heated; but their occurrence is too rare to merit consideration here.

Of the two first modes of communicating artificial heat, that by STEAM has been found much the best for warming the air of manufactories and dwelling-houses, from its greater regularity, from its susceptibility of being conveyed to any distance at an uniform temperature, and from the greater salubrity of the heat produced3. That

A Treatise on the Economy of Fuel, and on Heating and Drying by means of Steam, by Robertson Buchannan, vil Engineer. Glasgow, 1815.

Philosophical Works, by Shaw, articles Vegetation and Tobacco.

› See Buchannan's work above referred to: also Rees's Cyclopedia, art. Steam.

its introduction into hothouses would be attended with equally beneficial effects, a slight general comparison between steam and fire heat will show.

1. Fire heat is communicated to a hothouse by an arrangement which gives the power of heating a certain quantity of masonry, or metallic tubes, to an unlimited degree. If the heat is to be increased, it is produced by an increase of the quantity of fuel. The heat from steam is communicated by a similar arrangement; but as that fluid under common circumstances cannot be rendered hotter than boiling water, the thermometer applied to any part of a steam pipe generally rising to 190°, an increase of heat is produced by an increase of the surface to be heated. As quantity or dimension is obviously much more readily subjected to calculation than the effects to be produced on a flue or stove by increased combustion, there must be greater certainty and less risk of extremes in heating by steam than by fire.

2. In the best arrangements of flues in a hothouse, or of grates and stoves in rooms or manufactories, it is extremely difficult to equalize the temperature in every part of the heated space; that end of the flue nearest the fire always remaining the hottest, and may exhibit 500° where it enters the house, while fifty feet distant or at the other end it does not show 50°; because air and smoke, the two mediums employed to convey the heat from the fires, are the very worst conductors of heat. In the use of steam, even with no great attention to the distribution of the tubes, a perfectly equal temperature is constantly produced; be cause the vapour of water is the best known carrier of heat, and a tube filled with steam is no hotter at one yard than it is at one hundred yards from the boiler; but in every part of its length will raise a thermometer applied within an inch of the tube to 190° or 200 degrees.

3. Fire heat conveyed in flues gives out dust and smoke, mixed with decomposed atmospheric air, in quantities depending on the materials and workmanship of the flue. Iron stoves when heated intensely are supposed to decompose the watery part of the atmo

sphere, by which hydrogen gas is evolved, and an unwholesome and disagreeable smell produced. Steam is not liable to these bad effects: for the tubes of metal by which it is conveyed can be made so strong and tight as to prevent the escape of steam; and if even some were to escape, its effects in a hothouse would be favourable to vegetation, and in a house much less filthy and deleterious than smoke, dust, and hydrogen gas1.

4. Flues" such as we use," as Sir Joseph Banks judiciously observes, "waste in the walls which conceal them more than half the warmth they receive from the fires which heat them;" but by a judiciously contrived furnace and steam boiler very little heat will be lost. The œconomy of fuel therefore by steam must be very considerable. In a single pinery of ordinary dimensions, such as that at Kensington, it may be taken at more than three fourths of that used there; but where ten houses are to be heated from one boiler, the saving would probably be upwards of eight tenths. The saving in the first erection would be at least one half in an extensive range, though perhaps little or nothing in the case of a single house; and in all probability the saving in attendance and management would be as great as that of fuel.

If the advantages of heating by steam in hothouses are, or promise to be, so considerable, it may be asked why, having been tried for nearly twenty years, it has not become more general. To this I answer, that in respect to the trials mentioned above, they were exceedingly imperfect; and that the steam was applied more as dew or moisture, than as a vehicle for communicating heat. In the range of houses at Dalry, in which steam was so extensively used, fire heat was also employed in the usual manner and proportion; the boilers were

' Mr. Buchannan observes, that wherever steam had been adopted for heating the cotton mills, the persons employed, who used to be emaciated and sallow where stoves were used, had regained their health and assumed a fresh appearance. p. 207.

• Such as that mentioned by McNaught in Buchannan's work; or as greatly improved by Mr. Fraser at Kensington, and at Mr. Andrews's pineries, Vauxhall.