With the exception of Wren’s suggestions for ventilating the Houses of Parliament, and Sir Humphrey Davy’s actual installation of apparatus for this purpose, it was not until the last quarter of the nineteenth century that engineers turned their minds to this problem, in America. Yankee ingenuity had devised central heating before the Civil War, and one of the first numbers of Harper’s Weekly contained an article deploring the excessive warmth of American interiors; and at one time or another during the century, universal running water, open plumbing, gas, electric lighting, drinking fountains, and high speed electric elevators made their way into the design of modern buildings. In Europe these changes came reluctantly, because of the existence of vast numbers of houses that had been built without a mechanical equipment; so that many a student at the Beaux Arts returned from an attic in the Latin quarter where water was carried in pails up to the seventh story, to design houses in which the labor-saving devices became an essential element in the plan. It is only now, however, during the last two decades, that the full effect of these innovations has been felt. The economic outcome of all these changes can be expressed mathematically; and it is significant. According to an estimate by Mr. Henry Wright in the Journal of the American Institute of Architects, the structure of the dwelling house represented over ninety per cent of the cost in 1800. Throughout the century there was a slow, steady increase in the amount necessary for site, fixtures, and appliances, until, in 1900, the curve takes a sharp upward rise; with the result that in 1920 the cost of site and mechanical equipment has risen to almost one-half the total cost of the house. If these estimates apply to the simple dwelling house, they apply, perhaps, with even greater force to the tenement, the office building, the factory, and the loft: here the cost of ventilation, of fireproof construction, of fire-prevention and fire-escaping devices, makes the engineering equipment bulk even more heavily. Whereas in the first stages of industrial development the factory affected the environment of architecture, in its latest state the factory has become the environment. A modern building is an establishment devoted to the manufacture of light, the circulation of air, the maintenance of a uniform temperature, and the vertical transportation of its occupants. Judged by the standards of the laboratory, the modern building is, alas! an imperfect machine: the engineers of a certain public service corporation, for example, have discovered that the habit of punching windows in the walls of the building-machine is responsible for great leakages which make difficult the heating and cooling of the plant; and they hold that the maximum efficiency demands the elimination of windows, the provision of “treated” air, and the lighting of the building throughout the day by electricity.