some one who understood the laws of metals. The engineer was the man. The architect, seeing him spinning his suspension bridge, recognized that his was the knowledge wanted, and called him down to consultations about the building of houses. It was a new problem to the engineer, and he had to study its requirements; but it was a promising field, too, and he stayed. He studied architecture, and the architectural engineer was the result. In some conspicuous instances his conversion was so complete that his origin is almost forgotten, and he ranks among the leaders of his adopted art. But while the engineer was mastering architecture, the architect was working into the mysteries of engineering, and among the famous builders of any large American city to-day there are examples of the combination in three ways -the architect who has made himself an engineer, the engineer turned architect, and the firm with one member an architect and another an engineer.

The union of the two arts extended the

substitution of metal for masonry. The architect, blocked by the widening base of his brick walls, was taught that a slender pillar of iron could carry as much as his fattest mound. All that stone and brick were needed for was to protect the iron from fire and corrosion. In the superstructure the masonry need be no thicker than was required to give the frame-work rigidity. So they built, throwing more and more of the real work on the iron, and leaving off ever-increasing amounts of ma

sonry.

Without following the transition through the minuter changes, the movement may be divided into two periods, that of the double and that of the single construction. After all the saving of space that seemed possible in the details of pillars and girders, the building of high structures had risen only a story or two, and the demand for more of the free air and light continued. The next step was a brilliant one; the engineer suggested that iron could be made to carry the floors. This would relieve the walls of any weight but their own, and would reduce still further the space they must occupy all the way down the building. There would be two distinct structures the iron frame, which would be independent and complete in itself, and a shell

of masonry around it, closing it in to keep out the weather. They were fastened together, these two buildings, and supported each other somewhat, but theoretically either would stand alone so long as there was no wind or other side pressure.

When done, this revolutionary method of construction stood the test that was considered sufficient by the eager men who were trying to solve the modern architectural problem, and the financiers backed them for more. The price of lots in the neighborhood of the new buildings rose with them, in part because of them. The very solution of the old problem entailed a fresh one. The permanent financial question was revived in altered proportions. The builders overcame the difficulties of details, perfected their construction, and forged ahead a story or two by minor savings. But as the buildings grew in height even the separate walls, which had to bear only their own weight, increased at the base again, and presented the same old obstacle, a wall so thick on the most valuable floors that the rentable space was encroached upon to an extent that cut off below the gains in income above.

Why not let the iron frame that had carried the floors so easily take also the weight of the walls? It meant running the floor beams out under the masonry, a little strengthening of the columns, and it presented a pretty problem in handling windpressure. But these were matters of mathematics and engineering, not of rentable space. On the contrary, there would be a saving of room everywhere. It was tried on a small scale in New York in 1881, again on a whole building in Chicago in 1883, and during the next few years was gradually accepted everywhere as a profitable method of high construction on a narrow foundation. Steel was substituted for iron; hot steel rivets closed the connections and secured perfect rigidity, and gusset plates took the lateral pressure not distributable to the floors and interior columns. The steel cage assumed the whole burden of the sky-scrapers. The walls became a veneer, panels to protect the metals and the tenants from fire and weather. A Chicago architect recently began at the top, and put on his walls in succession downward to show that it could be done, and last year a builder in New York, whose

supply of lower-story stone was delayed by the cutters, closed in his upper floors while he waited.

Some architects are still afraid of the Chicago method, as the steel cage construction is called, and lean heavily when they can on their masonry, but for the lofty tower on a small base the steel cage is inevitable. No one can tell how long it will stand the test of time. There are 1,950 tons of steel in a building 370 feet high, which weighs in all 15,000 tons, and the metal will surely corrode; but how long before its sustaining strength will be vitiated to the danger-point is a question that no one can answer empirically, and the present generation of builders is not likely to know how well or how badly it has builded.

They can be sure of this, however, that they have solved their problem; they have reduced the cost of construction from about $5 to 37 cents a cubic foot; they can build as high as the elevator can go, and the elevator knows no limit. Legislation may interfere. The architects and builders themselves have invited legal restrictions to the height of buildings in several of the Eastern States. Otherwise, there is nothing in sight to check the rise of the sky-lines of the great cities. The financier talks of foundation costs and the increasing space required for elevators to serve more than thirty stories. All this means that the problem is back with the financier again, and that to go on would make necessary the combination of capital for the purchase of a large enough ground space to start with to give room for a solid bottom on which to build and plenty of inside room for the numerous elevators, local and express. A building thirty stories high has dug a hole for itself in New York; and, at the time of this writing, in the same city, the plans for fifteen buildings of fifteen stories or more were filed in the Building Department. One heard much grumbling about overdoing, and there was the rub; the builders had outstripped at last the rise of rents, which were handicapped by hard times.

But whether they go higher or not is a question beyond the present theme. The point is that they can. There are engineers who can lay the foundations for fifty stories; there are architects who can

plan the construction; there are builders who can realize the conception, and financiers who can manage the scheme. In short, brain can do its work when capital is ready and if the law permits.

The brain that is engaged in this business directly is divided into more than a hundred trades, each one of which has been developing its particular branch with the same strenuousness, boldness, and ingenuity that have characterized the architectural engineering. The architect himself has been laboring with a thousand considerations not even hinted at in this article. He has been studying out such other general problems as ventilation, light, economy of space, convenience, proportion, besides attending to special applications of all his principles, and those of all the other trades that entered the building with his, and add to the ever-varying problem. The engineers have been pondering such essentials as joinings and strains and foundations. In Chicago, where there is no hard pan within reach, they devised a floating "raft" of steel and concrete to lie flat on the shifting sands below the lake level, and on that they can build with such perfectly even distribution of weight that when the whole structure of twenty or more stories settles it sinks plumb. The elevatorbuilder has achieved such precision that the number of cars put into a building is determined by the cubical contents of the structure. The plumber has applied to his art the principles of sanitary science. The machinist has fitted his enormous plant to the dimensions of the cellar, and has plotted with the elevator man to use for the improved heating-system the exhaust steam from the power engines to warm the tenant after it has lifted him to his floor and lighted his room. The heater man has arranged so that all the tenant has to do is to set a gauge opposite the degree Fahrenheit at which he would like to have the temperature of his room kept, and the machinery automatically keeps it there.

So it is with the roofer and the tile man, the master mason and the carpentry man (no longer a mere carpenter), the manufacturer of hardware and the locksmith; the patent spring on the door closes it quickly, but prevents a slam, and the locks are exclusive for each door, with a master

key for the janitor. In one case, an armory, a set of locks was made with a private locker for each man, a master-key for all, and for each company another masterkey that would not open a locker in any other company-room.

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"I didn't realize there were so many trades in the world as I found I had to deal with when I undertook to finance this building," said the president of a corporation that had built a sky-scraper. But what amazed me most was the thought and the forethought and the cleverness that have gone into even the smallest things connected with a building, and the complicated perfection to which everything has been brought."

This financier, it happens, is one who attempted to manage the construction as well as the financing of his company's building, and, like many another expert manipulator of capital who has thought he could build an office building to pay, simply because he could put up a country house or run a railroad, he has paid heavily to learn that it is a distinct business, requiring special knowledge and training.

Just who the head expert should be-the real estate man, the architect, the builder, or the manager-has not been settled unanimously even in the trade, probably because the business is so new. Each of these can give good reasons why he should control, and in practice, first one, then another, appears as the master mind who hires the special service of the others. Again, all four and the engineer and the owner are combined successfully in one person; but in such a case the comprehensive talent builds to sell, not to rent, which is quite a different business.

The rule that is working out most satisfactorily to the investor, who knows only that he wants a building that will pay good interest on his capital, is to choose his experts, and form them into a committee, over which he himself presides to see to it that the best executive mind directs the work, while the considerations of the other specialists are regarded in proportion to their importance from the owner's point of view; or, if the owner cannot attend to it, to leave it all either to the real estate man who is to manage the building as a business after it is constructed, or to an architect who has built buildings that pay. Corporations appoint a committee of their directors, to which are added, one by one as they are chosen, the architect, the builder, and the manager. Individuals go first to