itself to this purpose if made "hollow" leading to such a flue. Sun-burners are efficient extractors when lighted.

To extract the foul air at the floor level, advocated by some theorists, is, we think, objectionable, and unsound in principle; as it is a law of physics that a gas expands and ascends when heated, the colder strata of air taking its place, we therefore think a system of ventilation which follows this natural order the best, and the ceiling level is for this reason the place for the exit of the vitiated air. The carbonic acid gas mixed with this air does not by its greater weight separate and fall to the lower level, as imagined by many writers, but tends by the law of diffusion of gases to diffuse itself throughout the room. To increase the circulation of this upward current in flues without fire, the draught may be maintained by gasjets or the flues warmed by other means. By the laws of hydrostatics, there is always a column of ascending air in a chimney or warm flue, the heavier column of colder air outside tending to take its place.* Hence, a fire-place offers the best means for perfect ventilation, and should be adopted in preference to openings in windows, &c., through which currents of cold air are continually entering, especially if no special admission is afforded at lower levels; and for the ingress of fresh air we would arrange openings either in the floor or through skirtings which may be warmed by flues or pipes in large buildings; or in the case of small apartments, inlets at the fire-grates, as noticed before. The "Manchester grate" is one of the best means yet devised of warming and ventilating several rooms by the waste heat of a single fire, and this is

*The draught or velocity of air in chimneys is found by formula:Velocity in feet per second=365/H (T-t); H being height of shaft in feet; T temperature of room; and t ditto of external atmosphere.

effected by warm-air flues of metal being carried up from the hot-air chambers surrounding the fire-box. By these warm-air flues good ventilation can be secured by valves or gratings in all the rooms so warmed.

But another mode of making the circulation complete in a house, is by converting the inner halls or staircases into warm-air chambers by stoves or hotwater coils, and thus diffusing through the rooms which open into those halls an equable flow of fresh warm air.*

By thus confining the heating apparatus to the halls in the first instance, the most copious supply of cold air is warmed before admission into the apartments, and the evils of draughty rooms averted, as there would not exist that continual rushing in of air to supply the fire-places under this system. We have adopted this system with success in some cases, and great economy of fuel is the result.

It will thus be seen a perfect system of ventilation is inseparable from warming, and both objects should be attained at the same time. It is the neglect of this mutual relation between the two objects which has been instrumental in impeding the advance of this great hygienic branch of construction.

The great principle may be shortly stated to be to provide means for the entrance of fresh air at a warm temperature and at a low level, and its extraction at a higher. Its removal is in proportion to the warmth of the apartment, compared to the external air if the natural system is adopted; or if heat is applied to accelerate, it will depend on the degree of heat, the law of equilibrium between the cold and warmer

*Ducts or channels behind the skirting may be provided for the passage of the warm air. A diffusion of warmed air from a basement chamber through proper flues opening into halls and rooms I believe to be the most economical system of warming.

atmospheres always tending to create a pressure towards the vacuum. So long as the incoming currents are rendered warm and imperceptible by entering through small and well-distributed apertures, the rapid circulation is harmless and promotive of health, but the evils of a strained, unprovided admission through crevices is perhaps more destructive to health than the want of egress. In summer-time these effects are not so apparent, though the two operations of ventilation-the removal of the foul air and the admission of the fresh-are still required.*

It may be useful to note that the respiration of one individual requires at least 500 cubic feet of air per hour; † and every cubic foot of gas requires 10 cubic feet of air and produces about 1 foot of carbonic acid.

In unions, hospitals, prisons, &c., it is usual to allow for day-rooms about 300 cubic feet of air to each inmate, and 1,000 or more cubic feet in the dormitories.

Among the appliances lately introduced for ventilating public rooms, the wards of hospitals, unions, &c., is the syphon ventilator, which consists of an outlet divided by a centre diaphragm, one compartment being a little higher than the other; by this means a circulation takes place, one compartment supplying the fresh air, and the other acting as an up-cast. A better plan, however, is to bring the fresh air through flues in external walls to hot-air chambers warmed by coils of heated pipe, the admission of air being regulated by valves. These grated openings should be placed vertically in the walls above floor level, the outlets being in ceilings near the warmest part of room, and so arranged

* In warm weather, the current of air is often reversed, as the air is more rarified outside.

+ Dr. Arnott thinks 20 cubic feet per minute necessary in soldiers' sleeping-rooms. In houses 600 cubic feet of space per adult should be allowed.

as to cause a cross-current through the room. Sheringham's ventilators are frequently used with success.

SECTION III.-HOUSE DRAINAGE, &C.

As the object of these remarks is chiefly confined to the consideration of drainage as it affects our houses, it will be unnecessary to enter into any detail of the main question of sewerage other than its bearing on this subject.

GENERAL SEWERAGE: GASES.-There is doubtless much room for improvement, though the pressing evils of the present system seem to me easily averted by proper means of provision in connection with our house drains, and I allude chiefly to large town systems of drainage, where it is more than ever necessary to exercise precaution. Especially is this necessary in low-lying districts and seaport towns, where sewers and drains frequently become tide or "water locked" during several hours every day, till the tide allows the escape of the pent-up sewage. Under the diluent system of disposing of our sewage-and this is at present the only practicable system of drainage available in large towns-there must ever be a large though varying volume of gas generated in the sewers, and pent up within them with no means of escape or relief, except through imperfect gullies, man-holes, and house-traps and drains. Through such vents this gas sometimes escapes, often to the injury of the public health, but especially to the occupants of houses. The pressure of this gas is very powerful at certain times, either from the displacement caused by the sewage water, heavy rainfalls, or by the temperature of the sewers. Now it is evident that the more secure and perfect the traps and pipes are that prevent the escape of this noxious gas, the more compressed and concentrated

is the gas, and the more eagerly it finds a vent through a weakly guarded passage or trap. Again, the modern system of draining our houses invites the admission of these poisonous gases in two ways. By virtue of the greater lightness of these gases (as nitrogen, sulphuretted hydrogen, ammonia, &c.), increased by the ascensional force created by the higher temperature of our houses, the cold drains empty their dangerous product into our water-closets and through our sinks, &c. Secondly, the arrangement of the pipes within our houses is another and perhaps greater source of evil. Our soil-pipes, for example, are generally in an upright position, and, stupidly enough, are by the present mode of construction actually stopped under our very noses by a water check, or "trap," as it is called, which is placed under every closet-pan, sink, &c. This water check, or seal, which is generally ineffectual, and often inoperative from various causes, becomes useless every time the closet action takes place, the downrush of matter allowing the free escape of foul gas through it. What a pitiable piece of human ingenuity, that allows admission to the most dangerous foe every time our closets are called into use!

REMEDIES.-Now what are the remedies proposed or existing for this crying evil, the most dangerous and deadly of our modern sanitary regulations? They may be summarised into three classes:-1st. Those remedies that remove the cause of mischief; 2ndly, those which deal with the main system of sewers and their outlets in relieving them of the gas, &c.; 3rdly, those remedies which may be applied to house-drains. They are either chemical or mechanical in operation.

Now one of the most important examples of the first class is that known as "Moule's Patent Earth Closet