tional Guard. It consisted of a concrete wall, three-quarters of a mile long, about six inches thick, twelve feet high and backed with earth. Every one hundred and forty feet was a little "marker's" house, where target supplies were stored. These houses were also to be of concrete.

Now at that time the colonel was a better marksman and constructive genius than contractor, and when he came to figure on his expenditures he found that he was going to lose heavily on the contract. He had not reckoned closely enough on the high price of the wooden forms. Rather than do his work at a loss, the colonel put in some hard thinking, and the idea came, "Why not mould. these rough walls in shallow trenches on the ground and lift them into place?"

The plan was tried out, a section at a time. All kinds of devices were used to raise the lengths into place after the concrete had set; derricks, cranes and jacks operated by hand power. Every step taken led to another in the right direction. The three-quarter mile wall was completed without the anticipated loss, practically no lumber being used.

Then came the time to construct the little marker's houses and instead of setting up forms for them, Colonel Aiken decided to try out his system on the simple walls of the sheds. The openings for the doors and windows were laid out, but before the pouring of the concrete was done the new idea had sprouted, "Why not set in the door and window frames and let the cement harden around them?" That was tried out with complete success. The walls of the little houses were raised and the corners locked by a method that was simple yet effective: the reinforcing material was allowed to project a few inches at the corners and, when in an upright position, moulds were set up at the junction of the walls and concrete was poured in, binding them perfectly. Thus, still more economy had been effected, and the little sprout of an idea had begun to develop into quite a promising plantlet.

When it came time to build the barracks at Camp Logan, a contract which the colonel had secured, it was decided to experiment still further and the new difficulties were overcome as they arose

until the present system was evolved, which is now in use by the Federal Government as well as in large private contracts all over the country. The apparatus in use at present consists of a series of latticed beams formed of angle iron, which stand about four or five feet above the ground on temporary foundations and work up and down on a pivot. Each beam is equipped with a telescope screw which is just of sufficient length to raise the frame to a vertical position. These beams are set along the inner side of the permanent foundation at intervals of about six feet or more, according to the proposed thickness of the wall. They are not perfectly horizontal but lie at an angle of about ten degrees. The wooden form for the wall is bolted upon them. You see, in perfecting the system, the lumber which brought forth the idea could not be altogether dispensed with, but as the form is built like a flat, shallow box, open at the top, only a little

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more than half the usual amount is required. Better still, that half is not nailed together by skilled carpenters but rapidly bolted in place by men who are not necessarily expert wielders of the saw and hammer. Best of all this lumber is not ripped to pieces and thrown away when the wall is up, but merely unbolted, fit to use again and again.

Having built the shallow box, set in the door and window frames and arranged for whatever ornament the façade is to have, the concrete is thoroughly tamped in about the reinforcement. Here is one of the greatest advantages of the system, as the pourers can readily fill every part of the form, while in an upright mould it would be comparatively easy for voids to remain.

Where the architect's plan calls for pilasters, ornamental capitals and decorative cornices or or friezes, these are allowed for. The highly decorative work is moulded separately and set in place,

covered with a cement finish after the concrete is hard enough to remove the forms, the result is often a surface which cracks and scales. By applying the finishing coat before the cement in the body of the wall is set the difficulty is overcome, as surface and wall become one piece. Various surfaces can be applied, of course, one of the most ingenious methods of producing an artistic finish. being by this method: a piece of old Brussels carpet is laid on the wet surface and immediately ripped off, leaving a semi-rough or stipple effect.

After the last touches are applied, the wall is allowed to harden and, as the upper surface is exposed to the air, this does not take long. Within five or six days the wall is set and ready to be tilted into an upright position on its foundations.

is exactly the same. This shaft makes 104 revolutions for every inch that it raises, so that the motion is very gradual and gentle.

The worm gear engages a telescope screw jack under each bench, the outer screw having a diameter of three and three-quarters inches and the inner one two and three-quarters.

Although the system has been in use for only a few years, many improvements have been made and many difficult feats attempted. One of the most remarkable exhibitions of skillful construction was the building of a church, the rear wall of which included a large curving apse. At first glance it would seem extremely hazardous if not impossible to tilt a wall with an eight foot bow in the middle of it, but it was a thorough success. arch of scaffolding was built upon a platform in the center of the regular wall form and the concrete tamped in place. Windows had been allowed for in the apse and these were boarded on the outside and guy wires were run from these boards to the benches in order to give greater rigidity to the apse while it was

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being tilted. In order to prevent the pull of this mass from uprooting the jacks bodily, they were securely anchored to a "dead man."

Another problem solved in connection with this system is the making of hollow walls of concrete. The necessity for the hollow walls in the severe cold of winter was demonstrated by a church which was built with a heavy solid wall of concrete. This was erroneously thought to be a sufficient non-conductor but the architects discovered their mistake when it was too late. The inner wall had been plastered, and elaborate and costly mural decorations had been applied to the interior, and when the church was heated for Sunday services the first real cold day of winter little streams of water ran down to walls, ruining the artist's work. The explanation was simple: the moisture contained in the heated air was condensed the moment it struck the cold wall of the

church and a liberal dew was precipitated upon the mural paintings.

The problem of obviating such difficulties by use of his system gave Colonel Aiken much food for thought. It was not practicable to make wooden forms to hold the inner and outer walls apart, as the lumber could not be removed, and if allowed to remain it would swell in wet weather and crack the cement. He had the fleeting idea of using tapering forms of sheet iron, which could be drawn out when the concrete hardened, but one day when going through his foundry he noticed the core makers preparing cores of sand, and the problem was solved. In preparing a hollow wall at present, the inner surface is poured first, together with concrete ribs for studding, which run up and down; then a thickness of dry sand is spread upon this to the required depth, flush with the studding, and the outer wall is poured on top of that.