perature. The third column shows the quantity, in grains, that would be evaporated in one minute, if the air had no moisture in it; and the fourth column shows the temperature of the air corresponding to this degree of evaporation, when the evaporating fluid is not supplied by extraneous heat.

A few examples will show the application of this table. 1. If the temperature of the air be 64.5°, then opposite 64.5 in the fourth column we find 11.4 grains for the evaporation in a minute when the air is dry; but if it has been ascertained that the dew point is at 37°, look opposite 37° in the fourth column, and the evaporation corresponding to that temperature is 5 grains. Take the difference between these, that is, 114-5-64 grains per minute will be the evaporation from a superficial foot when the temperature is 64 and the dew point 37°.

If the grains evaporated in a minute be divided by 600, the result will very nearly express the inches in depth evaporated in an hour, in a still atmosphere.

2. In an atmosphere where the dew point is at 42.3 and the temperature 70-5°, required the depth of water evaporated hour? This will be the difference between 13.8 and 5'8, or 8 grains per minute. Now is 0134 inches per hour, or a little more than 3 tenths of an inch in 24 hours.

per

3. A forcing house contains 4000 cubic feet of air, and it is desired to know the quantity of water that would saturate it, the temperature being 70°.

Opposite the temperature 70° in the first column, the moisture which combines with a cubic foot of air at 70° is 7.8 grains, and 7.8 x 4000 is 31200 grains.

4. If the ventilation of a house be 300 cubic feet per minute, and the dew-point of the air admitted be 32° required the surface of water that would maintain the dew-point of the air in the house at 50 when its temperature is 70°?

When the dew-point is at 32° we find each foot of air contains 2.3 grains, and at 50° it contains 4 grains, the difference has therefore to be added by evaporation, but 4-2.3 is 1.7 grains, and 300 x 1.7 is 510 grains. The evaporation from each foot at 70° is nearly 13.8 grains, and at 50° about the mean between 6.8 and 7-8, or 7.3 grains, therefore 13.8—7.3 is 6.5 grains from each foot of surface; and as we have found that 510 grains will be required in that time, we have the quantity by dividing 510 by 6.5, which is very nearly 80 feet of surface.

By this time the reader will have felt that an important inquiry is but slightly entered into, it requires a more complete table, and experiments on the evaporation from moist earth, leaves, &c. to render it more useful. It is not to artificial atmospheres alone that the investigation applies, it may be extended to the face of the globe, and may enable us to trace the effects of cultivation, of stagnant waters in confined districts, and the proper distribution of wood, cultivated land, and water which will preserve a healthy element. Men, as well as plants, feel the exhausting influence of dry air, or perish under the effect of a cold and saturated atmosphere, and perhaps a warm and saturated one is equally noxious.

Those who are acquainted with the researches of Mr. Dalton, on evaporation, will find that his experimental analogy is abandoned, and the subject referred to those first principles which must be involved in the question; and I trust I have done sufficient to show the basis of an accurate theory.

Mr. Dalton's analogy gives nearly true results in low temperatures, but in high ones it is very erroneous; besides not accounting for the well known depression of temperature which must take place where the heat is not supplied from an artificial source.

43

ART. XII. On the Cultivation of Vines in the open Air in Great Britain. By R. A. SALISBURY, Esq., F.R.S., L.S., H.S., &c.

MANY years ago, the writer of this paper had an extensive range of glass-houses, built chiefly for the cultivation of exotic trees and plants, half of which being removed into the open air for seven months, the rafters were devoted to training vines along them; and the climate being cold and soil unfavourable, namely, one of the more barren districts of Yorkshire, some of the grapes never ripened well, no artificial heat being given, as a far more abundant supply than was wanted, ripened in his other frames and hothouses. A very large brick building adjoining this range of glass was covered entirely with a single vine of the miller's grape, and as it was ornamental to the building, it was pruned and trained yearly, at no trifling expence, though it very seldom ripened twenty bunches out of from 1000 to 2000, which it annually bore.

A Scotch nobleman, who often visited the place, one autumn made the following remark, and, I believe, nearly in the following words: "When I was a young lad, I remember eating ripe grapes from a vine in the open air near Stirling Castle, which was brought to ripen half its crop in most summers, and a whole crop in warmer summers, by the following treatment: On the 20th of September prune the vine as you would in the month of December, taking off all the leaves and grapes, ripe or unripe, and shortening all the branches to 1, 2, or 3 eyes at most. The following spring it will push its buds a few days before any neighbouring vines pruned in winter. Train it as carefully all summer as if you was certain it would ripen its crop of fruit. Pursue the same system annually, pruning the tree always between the 20th and 30th of September, and in the course of seven years, you will be rewarded for your patience and expence, with half a ripe crop in most summers, and a whole ripe crop in warm summers."

This mode of treatment was immediately begun in his lordship's presence, and five years afterwards some excellent wine was made from the grapes.

are

The only remarks I have to add to your intelligent readers,

1st, That sage prince of gardeners, as Linné called him, Philip Miller, informs us, that if the vineyards in the north of France are neglected, it takes seven years' careful pruning and proper treatment to make them ripen their crops of fruit.

2dly, The experienced president of the Horticultural Society has found that all vegetables, which require to be left in a state of inactivity during winter, vegetate sooner in spring,

if that state of inactivity is brought on sooner in autumn; hence, though the winter of 1824-5, was so mild, that a small leaved myrtle and geranium zonale survived in the open air in the court of the writer of this paper near Bryanstone Square, the spring flowering plants and shrubs, and even the almond trees, blossomed remarkably late, considering the temperature of the season; and what is still more to the point, he observed winter aconites and crocuses in blossom from north of the river Trent so far as York, where the winter had not been so mild as in the southern counties, but several days of continued frost and snow had occurred; those flowers, with the mezereon being uch more advanced than in the gardens and nurseries about London, which were visited the day before he left London.

3dly, To any person, who wishes to pursue this mode of hastening the maturity of grapes, north of Stamford in Lincolnshire, he recommends the cultivation of the miller's or Burgundy grape exclusively; for he has found it unaffected by smart frost, when the shoots of the muscadine and sweet water were injured; and this is easily and physically accounted for by the very thick wool of its young shoots.

4thly, In the more southern counties, where many varieties of grapes ripen better, still an attention to the practice now recommended will ensure a superior flavoured crop, and some of the very best Grisly Frontiniacs, he ever tasted, were produced in the late Earl of Tankerville's garden, at Walton upon Thames, when under the care of Mr. John Dudgeon, who afterwards lived with Dr. Fothergill.

ART. XIII. On the Culture of the Huntingdon Willow, Salix alba, as a Timber Tree. By MR. ARCHIBALD GORRIE, C.H.S., &c. of Annat Garden, Perthshire.

THERE are few subjects connected with rural economy of more national importance, or more generally interesting than the rearing of timber. The purposes to which the propelling power of steam has been recently applied in navigation, and as an auxiliary in many of the arts, together with the immense quantities of coal used for furnishing gas in great towns, have produced a rise in the price of coal of from 15 to 20 per cent within the last twelve months; a demand in many places for brushwood to be used as fuel, with a corresponding rise in price, has been the consequence; a demand, which in many districts, the state of plantations is but ill calculated to meet. The present demand for timber also, for ship-building, and for

improvements going forward in the island, is unprecedented; consequently wood of every description is becoming every day more valuable.

When a man of wealth employs his capital in any ordinary speculation, or in any of the joint stock schemes of the day, he calculates on an early return; but he who lays out his money in the rearing of timber, has no stimulus but the interest he may have in the soil, or in the welfare of posterity. Hence, where we see an estate that is likely to descend by entail to an heir at law of a distant relationship, we find that the operation of planting is seldom engaged in to any great extent, unless it be with a view to burden that estate with a proportion of the expence on such improvements, in favour of nearer or dearer collateral branches of the family; and wherever we see the operation of planting entered into under such circumstances, the future management of the plants is too frequently neglected.

There are, indeed, several of our most useful trees, which require the lapse of ages before they arrive at a state of absolute maturity; but there are others of more rapid growth, which acquire considerable magnitude, within the natural period of human life, and which may, in the natural course of events, be cut down a full grown tree, by the same hand by which it was planted. The most distinguished of these, and the one which seems most to deserve public attention, I conceive to be the Huntingdon willow, Salix alba, of English botany, of which there are several varieties.

The uses to which the timber of the Huntingdon willow are applied are various. In ship bottoms it is not found so liable to split by any accidental shock as oak or other hard wood. It is found an excellent lining for stone carts, barrows,&c. In roofing, it has been known to stand an hundred years as couples, and with the exception of about half an inch on the outside, the wood has been found so fresh at the end of that period, as to be fit for boat-building. Its bark is used by the tanners and there is no tree that in the same time will yield so much bark for fuel, or that requires less labour in preparing it for the fire, where it gives out most heat when burnt in a green state; and to all this it may be added, that its cultivation is the most simple, while it will luxuriate in most soils, where other trees make comparatively slow progress.

As a proof of what is stated above respecting easy culture and rapidity of growth, I may remark, that it is only fourteen years next February, since I was engaged in planting a piece of rising ground on the estate of Rait, on the northern bank of the Carse of Gowrie. The soil a dry gravel, which effervesced freely with acids, the bank formed a slope of 45° with