this time the air inlets which opened into the two sides at the B end, and into the B end itself, were under reduced pressure, the consequence being that one minute the air in the classrooms was stifling hot, the next a deluge of cold air mixed with foul air products rushed into those classrooms which had the largest outlets, and where the aspirating action of the wind was most pronounced. The intermittent air currents so formed were very troublesome and unpleasant. The arrangement of the classrooms and the central hall were very good. The distribution of the hot water apparatus was passable, and the carrying over of the air outlets from the classrooms to the shafts, S S, very judiciously planned. After inspecting the building one could not help being pleased to see everything in such order, but appearances are often deceiving. One of the chief faults in the ventilation was the frequency and ease with which down draughts occurred in the shafts, S S, which were of much greater area in the aggregate than the inlet gratings when the wind was blowing from any quarter, and if any of the inlet gratings were shut the mischief was naturally aggravated. The considerable height of the air shafts made the down draughts and intermittent air currents more pronounced and unpleasant. The shafts, SS, were not properly protected from wind effects at the top, and the larger shafts of this kind are, the more such protection is needed. Some appliances were required to reduce the area of the shafts at the top during cold weather, and this last precaution was very necessary. The air inlet gratings should be protected from wind effects, and proper precaution taken to make sure that a strong wind did not disturb the direction of the air current in the outlets to the shafts. The area of each outlet from the classrooms, and from the hall, required to be adjusted according to the tension which was necessary, and according to the extra friction entailed by carrying the outlets over into the shafts from the classrooms farthest away-a very important precaution. Heat

applied in each shaft just above the air outlets of the classrooms on the ground floor would render the air current in the shafts more powerful, and less sensitive to the action of the wind, but a good fan in each shaft would be still more serviceable.

From what was said in Chapter IV., and the illustrations given of various buildings, and taking into consideration the further drawings and references in this chapter, it is thought that the types of most public buildings have been mentioned, whilst the action of the wind, and the intermittent character of the air currents, have been pointed out in detail. If the caretaker will consider these movements of the wind, and of the air inside buildings, and carefully compare the results with those which take place inside that over which he has charge, it ought to be possible to remedy some of the evils which lead to unpleasant down draughts.

CHAPTER VI.

HOW THE VENTILATION CAN BE IMPROVED IN BUILDINGS ALREADY ERECTED.

CONSIDERATION will be given first to the exit spaces and ventilators in or above the roof. Many churches like Figs. 12 and 13 are better ventilated than those which have ventilators in or upon the roof, and it would appear that the crevices and interstices in the boarding or plastering between the rafters were ample in total area to afford exit for all air getting into the building at the floor level. And this is the case in nearly all high buildings unceiled to the second principal bond. Where there is no ceiling, and the rafters are simply covered with match-boarding, the area of the outlet crevices in the roof will be generally far in excess of what is wanted in cold winter weather, no matter whether the tiles are boarded underneath in addition, or whether the slates have their joints plastered. The great heat absorbed by the slates during the summer simply cracks all the plastering, whilst the woodwork shrinks greatly and matchboarding is like a sieve to air under slight pressure. Where the roof has had felt laid upon boards under the tiles, and the joints of the felt have been made air tight, the air outlets will be under command; but, owing to defects in joining the felt, most buildings so provided have much outlet spaces notwithstanding.

Whether there are ventilators in the roof or not, attention should be given first to the condition of the building

during very cold weather-say at 40° F. or less, in order to see whether the crevices in the roof are too many in themselves to carry off the foul air when the outside temperature is so low. If the crevices are too numerous, some of them should be stopped up so that there should be no down draughts or perceptible air movements at 40° F. The down draughts generally increase in new buildings which are unceiled, and in which match-boarding is employed, by reason of the continued shrinking of the timber. Thick brown paper and strong paste and glue can be applied with effect, and the wet paper should be wrinkled loosely so as not to dry strained, or crack when dry, but it is unwise to paste over the crevices promiscuously, as it is best done in that portion of the building where the down pressure is most strongly exerted.

In many churches and other buildings hot water pipes are laid below the floor, and some provision made to let fresh air come from the outside; but, in consequence of the roof being timbered inside and shrunken by the heat, cold air streams so freely from the roof in the winter that the fresh air inlets below the pipes either do not act at all, or only fitfully and at intervals. The audience is thus caused to breathe the raw air from the outside, tempered only by being mixed with the warm exhaled products which are caused to descend to the hot water pipes to be further heated, and sensitive persons suffer repeatedly from colds in consequence of the swirl and up and down movements in the air.

It is most essential, therefore, that the combined area of the exit crevices in the roof should be ascertained and their outlet value determined, when the temperature of the air outside is low, so that proper regulation shall be made. If it is found when the ventilators are closed that the area of the cracks and crevices is sufficient or excessive, the provision which is made for closing any ventilators on the roof should be carefully examined in order to make sure that no undue

leakage occurs from deficient valves, and that arrangements are made for closing them perfectly. As the valves for closing ventilators are generally provided by the builders, they are usually of the pattern known as the butterfly valve, Fig. 22, which is a plate of iron cut to fit the ventilating tube, and having an iron rod across its diameter which passes through the walls of the tube, so forming pivots whereby the iron plate can be tilted from the outside. The valve is

generally weighted so as to be self-opening, whilst it can be shut by pulling a rope attached to a crank on the iron rod shown above. The valve opens as soon as the cord is released, and is shut when the cord is strained tightly, being prevented from turning round by a stop riveted in the walls of the outer tube. But how seldom is this tightness obtained! Careless straining of the cord leaves perhaps one-fourth of the area of the tube open, and down draughts are frequently