To determine the extent to which water should be introduced, and the character which it ought to assume in small places, is a point requiring some consideration. In the case of a spring or a running stream the difficulty is not great; but, where there is only just a sufficient supply of water to maintain a pond or small lake during the summer season, the akin required is greater. The difficulty arises, not from any doubt of the effect of the water, in a picturesque point of view, for that is easily determined; but with regard to its influence on the salubrity of the atmosphere of the place. The exhalations, even from pure water, when they are taken up by the atmosphere of any given space to such an extent as to render it moister than that of the surrounding country, must be considered injurious; and much more so are exhalations from water rendered impure by the decay of vegetables along its banks, or by the admixture of impurities from the drains of offices, etc. Attentive observation, and some experience on this subject, have enabled us to arrive at the following conclusions, which may be considered as principles: - Water should never be introduced in landscape gardening, unless it conduces to health, beauty, or picturesque effect.

285. With a view to health, water ought never to be introduced where it will increase, in any sensible degree, the quantity of moisture that would otherwise be taken up by the atmosphere of the locality, either in summer or winter. From this principle the following rules may be deduced:

1. That the surface to be covered with an artificial piece of water should be small, m proportion as the general surface of the ground is flat; the soil retentive; the park, pleasure-ground, or enclosure, small; and the trees and shrubs numerous.

S. That the most wholesome situations in which artificial water can be introduced, are those where the general surface of the ground is elevated, and the soil naturally dry, and not thickly covered with trees and shrubs.

3. That, in flat situations with retentive soils, where the surface is thickly planted with trees or shrubs, water, even on the most limited scale, should never be introduced, without, at the same time, rendering the surface of the surrounding ground perfectly dry by the frequent drain system.

4. That in no description of artificial water ought the decay of vegetables to be allowed to take place, and more especially along the margin.

5. That the margin of all artificial pieces of water ought to be formed of a considerable thickness of gravel or small stones, or of blocks of stone, in imitation of rockwork; in order to diminish the quantity of spongy or marshy matter, by which evaporation never ceases; and substitute for it a smooth hard surface, from which evaporation will go on with rapidity, and which will thus soon become quite dry.

Gardeners are in the habit, when they plant out pelargoniums, and other spongy-wooded green-house plants, on lawns, to reduce them before planting out to single stems, and to free these from leaves to the height of 8 or 4 inches. After planting, the surface (which forms a very gentle knoll, about 1 ft. in diameter, and, say, from 1 in. to 2 in. high in the centre, where the stem is placed) is bedded over with small pebbles, about the size of pigeons' eggs; and these, by drying rapidly after rains, prevent the damp from lodging about the collars of the plants, which, without this precaution, would, as it is technically called, damp off Now, if gardeners would apply the rationale of this practice to the margins of basins, ponds, lakes, rivers, and all pieces of water whatever, natural or artificial, in pleasure-grounds, they would render the evaporation from these pieces of water wholly innoxious. The evaporation from clear water is simply injurious by increasing the quantity of moisture held in suspension by the atmosphere; but the evaporation from water containing a mixture of decaying vegetables from the park above it, contains, in addition to water, those deleterious gases known as malaria.

As all pieces of water are liable to rise or fall with rains or great droughts, the breadth and height of the space along their margins, which is gravelled or covered with stones, ought to be such as that, in the greatest drought of summer, when the water is sank to the lowest point, it should not expose any of its earthy bed to the air; and that, in spring and autumn, when it is raised to its greatest height by rains, it should not touch the leaves of the plants along its margin. This is the beau ideal mode of treating artificial water, where the object is to render it wholesome; and it is gratifying to find that it is as superior to the common mode of treating the margins of pieces of water, in its accordance with the principles of picturesque beauty, as it is with the principles of health.

6. That, in distributing the trees and shrubs over a park or pleasure-ground containing a piece of water, provision should always be made for the exit from the grounds of the vapours which arise from the watery surface. This is to be done by broad spaces of lawn or turf without trees, extending from one or from both ends of the piece of water, through the park or pleasure-ground, to ground on a lower level (see fig. 99.), where the air charged with vapour will find its way by its own gravity. Where this is neglected, parks in low moist situations, with trees scattered regularly over their surface, become covered with what may be described as one general pond of malarian vapour; or with a number of ponds, in which the vapour is dammed up by trees crossing the course which It would naturally take along the lowest level. The gardens of the New Palace at Pimlico may be considered as one immense pond of malarian vapour, confined by the palace and other buildings at the lower end, and by high walls along the sides; and which is prevented from being dispersed by winds or the sun, by the groups of trees, mounds, grassy banks, etc contained in the interior.