A course of lectures on sanitary engineering has been delivered during the past few weeks before the officers of the Royal Engineers stationed at Chatham, by Captain Douglas Galton, C.B., D.C.L., F.R.S.

The refuse which has to be dealt with, observed Captain Galton, whether in towns or in barracks or in camp, falls under the following five heads: 1, ashes; 2, kitchen refuse; 3, stable manure; 4, solid or liquid ejections; and 5, rainwater and domestic waste water, including water from personal ablutions, kitchen washing up, washings of passages, stables, yards, and pavements. In a camp you have the simplest form of dealing with these matters. The water supply is limited. Waste water and liquid ejection are absorbed by the ground; but a camp unprovided with latrines would always be in a state of danger from epidemic disease. One of the most frequent causes of an unhealthy condition of the air of a camp in former times has been either neglecting to provide latrines, so that the ground outside the camp becomes covered with filth, or constructing the latrines too shallow, and exposing too large a surface to rain, sun, and air. The Quartermaster-General's regulations provide against these contingencies; but I may as well here recapitulate the general principles which govern camp latrines. Latrines should be so managed that no smell from them should ever reach the men's tents.

To insure this very simple precautions only are required:

1. The latrines should be placed to leeward with respect to prevailing winds, and at as great a distance from the tents as is compatible with convenience. 2. They should be dug narrow and deep, and their contents covered over every evening with at least a foot of fresh earth. A certain bulk and thickness of earth are required to absorb the putrescent gas, otherwise it will disperse itself and pollute the air to a considerable distance round. 3. When the latrine is filled to within 2 ft. 6 in. or 3 ft. of the surface, earth should be thrown into it, and heaped over it like a grave to mark its site. 4. Great care should be taken not to place latrines near existing wells, nor to dig wells near where latrines have been placed. The necessity of these precautions to prevent wells becoming polluted is obvious. Screens made out of any available material are, of course, required for latrines. This arrangement applies to a temporary camp, and is only admissible under such conditions.

A deep trench saves labor, and places the refuse in the most immediately safe position, but a buried mass of refuse will take a long time to decay; it should not be disturbed, and will taint the adjacent soil for a long time. This is of less consequence in a merely temporary encampment, while it might entail serious evils in localities continuously inhabited. The following plan of trench has been adopted as a more permanent arrangement in Indian villages, with the object of checking the frightful evil of surface pollution of the whole country, from the people habitually fouling the fields, roads, streets, and watercourses. Long trenches are dug, at about one foot or less in depth, at a spot set apart, about 200 or 300 yards from dwellings. Matting screens are placed round for decency. Each day the trench, which has received the excreta of the preceding day, is filled up, the excreta being covered with fresh earth obtained by digging a new trench adjoining, which, when it has been used, is treated in the same manner. Thus the trenches are gradually extended, until sufficient ground has been utilized, when they are plowed up and the site used for cultivation.

The Indian plow does not penetrate more than eight inches; consequently, if the trench is too deep, the lower stratum is left unmixed with earth, forming a permanent cesspool, and becomes a source of future trouble. It is to be observed, however, that in the wet season these trenches cannot be used, and in sandy soil they do not answer. This system, although it is preferable to what formerly prevailed - viz., the surface defilement of the ground all round villages and of the adjacent water courses - is fraught with danger unless subsequent cultivation of the site be strictly enforced, because it would otherwise retain large and increasing masses of putrefying matter in the soil, in a condition somewhat unfavorable to rapid absorption. These arrangements are applicable only to very rough life or very poor communities.

The question of the removal of kitchen refuse, manure, etc., from barracks next calls for notice. The great principle to be observed in removing the solid refuse from barracks is that every decomposable substance should be taken away at once. This principle applies especially in warm climates. Even the daily removal of refuse entails the necessity of places for the deposit of the refuse, and therefore this principle must be applied in various ways to suit local convenience. In open situations, exposed to cool winds, there is less danger of injury to health from decomposing matters than there would be in hot, moist, or close positions. In the country generally there is less risk of injury than in close parts of towns. These considerations show that the same stringency is not necessarily required everywhere. Position by itself affords a certain degree of protection from nuisance. The amount of decomposing matter usually produced is also another point to be considered. A small daily product is not, of course, so injurious as a large product. Even the manner of accumulating decomposing substances influences their effect on health. There is less risk from a dung heap to the leeward than to the windward of a barrack.

The receptacles in which refuse is temporarily placed, such as ash pits and manure pits, should never be below the level of the ground. If a deep pit is dug in the ground, into which the refuse is thrown in the intervals between times of removal, rain and surface water will mix with the refuse and hasten its decomposition, and generally the lowest part of the filth will not be removed, but will be left to fester and produce malaria. In all places where the occupation is permanent the following conditions should be attended to:

1. That the places of deposit be sufficiently removed from inhabited buildings to prevent any smell being perceived by the occupants. 2. That the places of deposit be above the level of the ground - never dug out of the ground. The floor of the ash pit or dung pit should be at least six inches above the surface level. 3. That the floor be paved with square sets, or flagged and drained. 4. That ash pits be covered. 5. That a space should be paved in front, so as to provide that the traffic which takes place in depositing the refuse or in removing it shall not produce a polluted surface.

In towns those parts of the refuse which cannot be utilized for manure or otherwise are burned. But this is an operation which, if done unskillfully, without a properly constructed kiln, may give rise to nuisance. One of the best forms of kiln is one now in operation at Ealing, which could be easily visited from London.