How to remove the heated, vitiated air and to supply fresh air while maintaining the same uniform temperature is a problem of long standing. The history of the attempts to heat and ventilate the Houses of Parliament since Wren undertook it in 1660 has justly been said to be history of the Art of Ventilation since that time, as the most eminent scientific authorities in the world have been engaged or consulted in it, and the most exhaustive reports on the subject have been rendered by such men as Gay-Lussac, Sir Humphry Davy, Faraday and Dr. Arnott of England and Gen. Morin of France. The same may be said in regard to the Houses of Congress in the United States Capitol for the past thirty-five years. Prof. Henry, Dr. Billings, the architect, Clark, of that country, and many other bright inventors and men of ability have given the subject devoted attention. Among the means for creating ventilation are underground tunnels leading to the outer air, with fans in them to force the fresh air in or draw the poor air out, holes in the ceiling, fire places, openings over the doors, openings under the eaves, openings in the window frames, shafts from the floor or basement with fires or gas jets to create an upward draught, floors with screened openings to the outer air, steam engines to work a suction pipe in one place and a blow pipe in another, air boxes communicating with the outer air, screens, hoods, and deflectors at these various openings,--all these, separately or in combination, have been used for the purpose of drawing the vitiated air out and letting the pure air in without creating draughts to chill the sensitive, or overheating to excite the nervous. There seems to have been as many devices invented to keep a house or building closed up tight while highly heating it, as to ventilate the same and preserve an even, moderate temperature. The most approved system of ventilation recognises the fact that air is of the same weight and is possessed of the same constituents in one part of a room as at another, and to create a perfect ventilation a complete change and circulation must take place. It therefore creates a draught, arising from the production of a vacuum by a current of heat or by mechanical means, or by some other way, which draws out of a room the used up, vitiated air through outlets at different places, while pure outer air is admitted naturally, or forced in if need be, through numerous small inlets, such outlets and inlets so located and distributed and protected as not to give rise to sensible draughts on the occupants. The best system also recognises the fact that all parts of a house, its cellars and attic, its parlours and kitchens, its closets, bathrooms and chambers, should be alike clean and well ventilated, and that if one room is infected all are infected.