ured for a series of years at the site of the dam ranges from two hundred cubic feet per second in the dry season to 6,000 cubic feet in May and June, when it is filled with the waters from the melting snow of the mountains. The work must be strong enough to resist the enormous force of the flood currents also planned to divert the surplus water in an emergency and thus aid in relieving the pres

sure.

This is why the embankment forming the reservoir, when completed will be by far the largest yet planned in this country and the greatest in the world for restraining and conserving a river. The figures give an idea of its dimensions. At the center it is no less than 789 feet in thickness, rising to a maximum height of 140 feet above the natural bottom of the river, while the length of the main dam is 623 feet. To this, however, is added an earth dike 2119 feet long extending from the west side, forming a barrier to hold back the overflow of the flood where it has but little current. Simply speaking, the work is an enormous fill. Compared with the great Roosevelt dam its base is nearly five times as great in width. It has what might

be called a "back bone" of steel but this is the only material in it that is not rock, sand, gravel and ordinary earth.

In creating the "Magic Dam," as it has been called, some very interesting preliminary work had to be performed. The engineers found they could economize time, labor and material by first preparing the sides of the gorge where they joined the barrier. Chambers were dug into each side to a distance of forty feet, all of the loose material such as sand, loose stone and fissured rock being cleared away, so that the ends of the dam would rest against the solid rock. A curious feature of this work was that the material removed was used for building up the "toes" of the two barriers which inclose the embankment-known as the up stream and down stream dams. Much of the composition of these dams was taken from the excavation in the canyon sides and the balance needed from quarries. The type of the dams is the rock fill and they were constructed from each side by dumping the rock and finer "spoil" from cars on tram roads reaching to the excavations. Portable derricks placed in position the larger rocks. By the plan an opening was left

for the river channel and the work was but slightly interfered with during high water. In July, 1909, the dams were so far advanced that advantage was taken of the low stage of the river to close them.

The first work done on the project, however, was the building of the diversion tunnel, cut through the west wall of the gorge, a distance of 591 feet, and lined with concrete. This tunnel is large enough to convey half of the river flow at flood and was built first in order to divert the river current at high water and minimize the pressure on the uncompleted works. It will be utilized permanently to serve the irrigating system. The method of receiving and distributing the water is by means of an intake tower. This is composed of concrete, is one hundred and thirty-seven feet above the foundation of the dam, and is designed in octagon form, to offer the least resistance to water pressure. The water from the reservoir enters the tower through several openings to minimize the pressure within, and is thus carried into the tunnel. The water reaches the tunnel through two water gates, five feet in diameter, which are operated by hand. This unique water distribution is connected with the embankment by a steel bridge of two spans each one hundred and fifty-three feet in length. When the engineers were ready to close the dams, this tunnel carried away most of the

river flow and the Bigwood was barred in July, 1909, as stated.

With the ends of the embankment completed the river channel between them became a pond which drained under the down stream barrier as an aperture had been made for letting it escape. Operations were now begun in building the "back bone" already referred to. A trench thirty feet wide and ten feet deep was dug along the axis of the embankment connecting with the excavations made in the side walls of the gorge. Into the trench for its entire length, was driven a row of steel sheet piling, down to solid rock, the top of the piling extending to a height of several feet above the top of the trench and ten feet upstream from the axis. This work was done to prevent any possible seepage of water through the embankments and is also intended as a reinforcement to the earth work.

The system employed is notable for its economy, and capacity, contrasted with what it accomplishes. The material is readily taken out by steam shovels moving on tracks. Such is their capacity that the shovels excavate 90,000 cubic yards a month with their automatic filling and emptying buckets. The spoil is dumped by the buckets into tram cars on railway tracks running to the material pits, then hauled to the edge of the fill where it is to be deposited or at some point up stream from the place it is to fill.

Then it is forced into the embankment by hydraulic jets-literally washed into position as the gold of the placer mines is extracted by the stream of water. One advantage of this method is that the filling is done more compactly and firmly than it could be formed by throwing in the material and grading it with the shovel or otherwise. As fast as the dump cars are emptied through their hopper bottoms, a stream of water is turned on the pile from the nearest pipe connection thus forcing it into the fill without the necessity of any human labor in grading or distribution. The drainage is such that the water leaves the newly made formation in a few hours.

As to the formation of the dams or borders of the work, the down stream structure was composed of large rock on the face, its inner slope being of smaller material worked into the crevices between the rock. In making the upstream face the finer filling material forms the exterior, the rock work thus being protected from the eddies and currents, and not directly exposed to the river. Thus in flood season the currents and eddies cannot work into the filling between the rocks beneath. In addition to the diversion mentioned, further protection against flood currents is an emergency spillway on the embankment. This is to be four hundred feet long and extend to a depth of four feet below the crest. A concrete weir has also been constructed, 1,600 feet in length to carry away surplus water. These works were only built after studying the river stages for a period of years and getting the depth of

A

N aerial trolley car, driven by a propeller and with a carrying capacity of fifty-six passengers, is in actual operation on a short stretch of track in one of the suburbs of Los Angeles, California. It is the invention of J. W. Fawkes, who has made a fortune from various patents.

The car has a length of fifty feet, is six feet wide and seven-and-a-half feet high. It is of a torpedo or cigar shape, with a propeller at one end, and is built of angle steel and aluminum.

It is suspended on an overhead rail of iron, three-and-a-half inches broad, and this is scientifically trussed with iron rods which are kept taut by a system of turn buckles. Trolleys above and below hold the car firmly to the rail. The track is suspended from twelve-inch wooden posts with iron bars, and these posts rest

on a firm foundation in the earth and are securely braced.

It is proposed to construct a double track system, one on each side of the central poles, so as to equalize the pull in both directions.

Probably the most remarkable feature of this aerial trolley is the propeller which drives it along the track. It is a radical departure from the type of propeller in use on aeroplanes, having two huge fan-shaped blades, which, the inventor claims, add greatly to the force of the thrust. The construction of the fanshaped blades is unique. They are of sheet iron, supported by frame work of seamless steel tubing. Each of these tubes is welded into a disk of aluminum, an inch in thickness and six inches in diameter, and the driving shaft runs through this series of fifteen aluminum disks like a core.