hand, where manures are applied as top-dressings in the solid form, it is proved by experience that after heavy showers of rain the solid manure is washed away, bodily as it were, into the ditches and watercourses; so that whilst the outfalls from land top-dressed and undrained are turbid with the matter carried away, and complained of as a nuisance, the outfalls from drained land, richly manured with the liquid, discharge pellucid streams."

Liquid sewage has a special value distinct from the fertilizing matter it contains, and also from the water that transports it; and this is its temperature. The value of this peculiar property cannot be over-estimated in a country similar to this, in which extreme changes of atmospheric temperature often take place suddenly, and injuriously affect both plants and animals, and this is more particularly demonstrated in the depth of winter and during long and continuous frosts. "It is a rather remarkable circumstance," observes Mr. Baldwin Latham, " that when the greatest degree of temperature is required the sewage possesses it, that is, the temperature of sewage has been found by the author to increase with the period of duration of frost. This is probably owing to the stagnation of surface-water, and also to the habits of the people, as much less cold water is used in the depth of winter than at other times. So great is the value of temperature, that a crop under sewage irrigation may be seen growing even at the time of a severe frost."

It does not appear that there exist any soils to which sewage irrigation may not be beneficially applied. That portion of the Craigentinny Meadows at Edinburgh known as Figgate Whinns, consists of absolutely pure sand, whilst the soil of other parts is a good loam passing into a strong clay; the former, which was originally worthless, now produces grass crops which sell at from 207. to 287. per acre per annum, thus showing that no land can be too poor for profitable cultivation where liquid sewage is obtainable in sufficient quantity. A larger amount of sewage is required for light than for heavy soils, particularly during the first year of its application; and clay appears of all others to possess the peculiar property of separating the manurial ingredients more completely, and of retaining them better, than any other soil, and it is consequently found that the crops grown are much heavier, and that altogether clay soils produce a far better result than those of a light, sandy nature. Gravelly soils require a certain time to become thoroughly saturated with the sewage, and absorb it greedily while the operation is in progress.

The value of a good system of drainage in all agricultural land is sufficiently understood at the present day; but if it be beneficial under ordinary circumstances, it is absolutely necessary where irrigation is adopted, especially in heavy soils. "I have no doubt," says Mr. Denton, in the letter above referred to, "that in cases of

sewage applied by way of irrigation to the surface of undrained clay land, or to water-logged free soil lacking natural drainage, the earth will become sodden, and liable to create a malaria; but with a perfect system of under-drainage (designed with relation to surface irrigation) at the first description of soil, and natural drainage in the second, sewage-irrigated land may be rendered perfectly harmless." From time to time complaints have been raised that land irrigated with sewage-water was offensive to the surrounding neighbourhood; the observations of the British Association Commission, however, tend to prove that in most cases the application of the sewage for irrigation has not been attended with any apparent change in the sanitary condition of the district, whilst in several instances there has been a marked improvement. Generally speaking, too, no objection appears to have been made to the application of sewage in this manner, and where such objections have been made, on the ground that the application was offensive and injurious, they do not appear to have been supported by medical authorities, and in several instances they have ceased.

The quantity of sewage that may be applied with advantage to an irrigated area in the course of the year has been closely investigated by Mr. Latham, and as the results of his calculations agree entirely with the experience obtained at Croydon, and with the experiments made by the Sewage Commission, we give them here as being probably the closest approximation to exactness yet obtained. Where it is considered desirable to apply as much sewage as will be sufficient for the growth of a grass crop, without drawing on the resources of the soil, 3645 tons of sewage per acre per annum will be required to grow 30 tons of grass, 4860 tons of sewage for a crop of 40 tons of grass, and 6075 tons for one of 50 tons of grass. If, however, the soil will provide half the potash required, then, to grow 30 tons of grass per acre, there will be required 1837 tons of sewage; to grow 40 tons of grass per acre, 2450 tons of sewage; and to grow 50 tons of grass per acre, 3062 tons of sewage. As 40 tons of grass per acre may be considered as easy of production on a properly-regulated irrigated area, and as it would not be desirable to exhaust the soil of any of its constituents, Mr. Latham considers that 4860 tons per acre may be said to be the right amount of sewage, and this closely assimilates with the conclusions arrived at by the Sewage Commission, who reported that 5000 tons of sewage per acre per annum was the right amount to apply in order to get the greatest results.

The actual value of town sewage yet remains, to a certain extent, an open question, but it may be accepted as a universal rule, that only under the most exceptionally favourable circumstances can the sale of it afford any adequate return upon the cost of constructing sewage works; so that, however profitable its use

may be to the farmer, it cannot be relied upon as a source of much income to the town whence it is obtained. The theoretical value of sewage has been calculated by some of our most eminent chemists and others, and the results arrived at vary from 1d. to upwards of 2d. per ton. Practically, however, it has been found that this is too high, and that its real value-that is to say, the price which a farmer could afford to pay for it--does not exceed from d. to 1d. per ton, and in estimating the probable returns from the sale of sewage it will always be safer to adopt the lower figure.

The cost of the application of sewage for irrigating land appears to be dependent on a number of local conditions, and, consequently, to vary considerably. It would seem, from the data collected by the Commission appointed by the British Association, that in many instances the outlay requisite for this purpose would exceed what a farmer could be expected to incur, and that in such cases, at least, it would be proper to regard this outlay as coming under two distinct heads, viz. that which a town may reasonably be expected to bear for the mere object of getting rid of its refuse, and that which a landowner or farmer may be able to incur for the improvement of his land. It is probable that when viewed in this light the application of liquid sewage to land would become a source of revenue to towns only under special favourable circumstances, but that, in opposition to the opinions which have been somewhat hastily formed in certain cases, it will more frequently entail some amount of expenditure on the towns themselves. At the same time the benefit to land and the improvement in the condition of rivers to be realized by this mode of dealing with liquid sewage can scarcely be matter of doubt or uncertainty any longer.

For carrying out a system of irrigation it is necessary, of course, that the sewage should, in the first place, be brought by channels or drains to the neighbourhood of the fields to be irrigated, where the more solid parts are separated from the liquid by allowing it to settle for a time, or, as is more generally the case, by a coarse system of filtration. For the distribution of the liquid, four different methods have been applied, viz.: 1. That known as the hose and jet system. 2. Sub-irrigation, or the distribution of the fluid below the surface of the ground. 3. By means of surface channels. And, 4. By total submersion. In deciding, however, which is the best system for distributing sewage, two things should be kept in view the first is that all arrangements for its distribution should be as simple and inexpensive as possible; and the second, that owing to the constant quantity of sewage to be dealt with, the arrangements must be capable of being worked at all times and seasons. With these preliminary remarks we proceed now to describe briefly the principles upon which the different methods of distribution, above referred to, are carried out.

In

1. The Hose and Jet System.-The fatal objection to this system is that it is not capable of application at all seasons. laying out works for the purpose, the sewage must, in the first instance, be brought into the field by means of underground pipes, which must also be laid in a sort of network over the whole grounds to be manured, to which pipes with couplings or hydrants for attaching a hose are fixed at certain points (see Vignette). In all cases where the hose and jet system is applied, the sewage must be delivered under pressure to enable it to be distributed over the field at a considerable altitude above its surface, as well as to overcome the friction in the pipes, and a head of from 10 to 12 feet is necessary where the sewage is delivered by the force of gravitation. Where a natural fall cannot be obtained, pumping becomes necessary, and this adds considerably to the cost. One great objection to the hose and jet system is that sewage cannot be applied to crops by it except at the earliest stages of their growth, owing to the necessity for dragging long lengths of hose over the land; it is therefore quite inadmissible when the crop has grown to any considerable height. Besides, by this mode of application the sewage is sprinkled over the crops, falling upon them as a shower, instead of being applied to the roots, which, though it would be unimportant and harmless were pure water only used, becomes actually injurious to vegetation in the case of sewage irrigation, by leaving certain deposits upon the leaves and stems of plants, which clog their pores and check growth. The system has enjoyed a partial success on the farms of Mr. Alderman Mechi and Mr. Nelson, but at Rugby, and other places, it has totally failed, and been abandoned. Mr. Rawlinson has stated that it would cost more to distribute 500 tons of sewage per acre by the hose and jet than it would to apply 5000 tons by surface channels.

2. Sub-Irrigation.-Under this system porous pipes, or tubes perforated with small holes, are laid under the ground at such a depth as to be beyond the reach of the plough, through which the sewage-water is forced. In some instances the pipes that are used for drainage may be made use of for this purpose by merely stopping up their outlets during the time that they may be required for irrigation, by which means the water will be dammed back until it reaches the upper stratum of the earth and the roots of the plants. This system has been practised in Switzerland to a limited extent; it is, however, expensive, and is open to the objection that it tends to raise the water in the land to the level of the soil, and the earth thus becomes water-logged, in addition to which it is attended with a great waste of fertilizing matter owing to the depth at which the sewage is delivered below the surface, a part of it gravitating still lower into the earth, and only a portion reaching the roots of the plants.

3. Surface Channels.-For the purpose of distributing sewage by means of open carriers, or surface channels, it may, if desirable, be brought to the head of every field in a covered channel, or it may be permitted to flow through open ditches, as may be most convenient. This system, which is the simplest and most effectual, may be carried out in various ways, according to the configuration of the land. By it sewage can be at all times applied to the plant, as it merely runs in a thin film over the surface of the ground at its root; but in all cases it is necessary that the land be specially prepared for the sewage by careful levelling, and otherwise according to its natural contour. This may be done in three ways, which are respectively known as the pane and gutter system, the catchwork system, and the bed system. The pane and gutter system is the best, and is admissible in all fields having a gentle rate of inclination. The land under this system is laid out, transversely between the open carriers that distribute the sewage, quite level; the sewage is brought to the head of the field in an open or covered main carrier running transversely across it, or in the direction of its least fall; the carriers for distributing the sewage branch out from the main carriers and run down the field in the direction of its greatest fall; the sewage is distributed over the intervening space between the distributing carriers by means of stops or sluices (see Fig. 1) being placed in the carriers, which dam back the

carriers at A (Fig. 2), which being dammed up at certain points are caused to overflow, the surplus water being carried away by the