A «lamp house is colder than a dry house, but a dry house is not necessarily «»f equable temperature. An iron building may be proof against the ingress of tenial moisture, but it will be cold in winter and hot in summer, for iron is a good conductor of heat. To prevent such extremes of temperature, iron churches are lined with wood, a material which conducts heat very slowly. A common illustration of the difference of the two materials in this respect is that of an iron poker and a wood brand, each with one end in a fire; the knob of the poker will sear the hand before the outer extremity of the wood becomes uncomfortably warm.

The relative thermal conductivity of different building-materials is, according to Peclet, approximately as follows: - Fir boards 1, plaster 2.8, brickwork 3'5, glass 4.8, stone 10, marble 18; and that of various metals used in building has been ascertained by Wiedemann and Franz to be as follows, silver being taken as the standard with a conductivity of 100: - Copper 73'6, brass 23.6, tin 14.5, iron 11.9, steel 11.6, lead 85. Water and air conduct heat only to a very small extent, air being one of the worst conductors known; hence Nature's devices of feathers, fur, and wool, and the human inventions of hollow walls, double windows, ceiled attics, silicate cotton, and cocoa-nut fibre packing.

The use of a bad conductor of heat in conjunction with a material which is a good conductor of heat but practically impervious to moisture, is exemplified not only in the lining of iron buildings with wood, but also in the boarding of roofs under slates or tiles. The slates and tiles are practically impervious to moisture, while the boards retard the ingress and egress of heat In the case of roofs, however, it is necessary to protect the wood from the moisture which may be driven by the wind through the joints of the slates or tiles, and this is done by covering the boards with a layer of bituminous felt or waterproof paper. This lessens both the pervionsness and conductivity of the roof.

Brick is a worse conductor than stone. Stone walls should therefore be thicker than brick if they are to prove the same protection from extremes of temperature. Doubtless it is for this reason that the Education Department insists on stone walls being 20 inches thick, while solid brick walls need not exceed 13 inches.

Plaster is a worse conductor of heat than either brick or stone. Not only, therefore, does it render a wall more sightly and amenable to decoration: it also adds to the comfort of the room.

Glass, on the other hand, is a better conductor than plaster and brickwork, and has the further disadvantage of being used in exceedingly thin sheets; it is the cause of more variation in temperature than any other portion of the structure of a house. The thickness of plate-glass is a point in its favour, and double panes are sometimes used, one on each side of the window-sash, in order to lessen the loss of heat through the window.

The superiority of lead over copper for roof-coverings, in respect of conductivity, is remarkably striking, but in practice the difference would not be much felt, as both are laid on boards which are themselves satisfactorily bad conductors. The colour of materials has some effect on their absorption and radiation of heat. White and black are the two extremes, and between them, in order of absorption, are pale-yellow, dark-yellow, light-green, Turkey-red, dark-green, and light-blue. The glittering whiteness of the buildings on the shores of the Mediterranean and in other hot countries helps to keep them cool in the flaming sunshine, while in manufacturing districts in England the dark-slated roofs of many of the mills and weaving sheds are covered in early summer with whitewash to reduce the heat of the rooms beneath, - practical applications of this law of colour.

In any house the least variation of temperature is found in the basement rooms or cellars, the greatest in the attics. The variation is especially noticeable in attics where the slates or tiles are laid on laths without felt or boards, and where the ceiling is not plastered. Because cellars are of equable temperature, it must not be concluded that they are the most healthy of habitations. On the contrary, they are usually very much the reverse: they are generally damp, the temperature although equable is low, and they are insufficiently lighted and ventilated. The healthfulness of a house does not inhere in temperature alone, but in many other qualities of varying importance.

Warming: and ventilation are, of course, the most important means of regulat-ing the temperature of a house, and in the ideal arrangement the inlet and outlet of air would be under perfect control, so that the temperature of the house could be nicely maintained in spite of external fluctuations. But the cost and difficulty of warming and ventilating a building will be minimized if its construction has been considered with reference to the laws of heat.

The motion of the air is an important factor in the effect which temperature has on the body. A still, cold atmosphere is not as trying to the constitution as air in motion, even though the latter be somewhat warmer. Cold damp winds are more chilling than keen frosty calm. And in a house the motion of the air must be considered in connection with its temperature. Draughts are deadly, or at the least provocative of more or less dangerous and uncomfortable colds. The prevention of draughts is a difficult problem. There is no royal road to it. Much depends on the general arrangement of the rooms and passages, and on the relative position of fireplaces, doors, and windows; much also on the actual construction of the building so that the external walls, roofs, and windows do not absorb and radiate too much heat from the rooms. But the most important factors in the prevention of draughts are proper warming and ventilation. The draughty room is that where the tire must draw its supply of air from door and windows and gaping floor- boards; two or three inlet-ventilators in suitable positions would lessen the draughts, and at the same time make the fire burn better Indeed, the air may be brought direct to a chamber behind the fire, and wanned there before being allowed to enter the room. Who does not know a room where the tire will not burn properly unless the door is left ajar? Un-wanned halls and staircases are prolific sources of draughts; it is false economy to leave these spaces without any arrangement for heating them.