concrete, which compacted very thoroughly, and by facing the water side of the dam with mortar put in at the same time with the concrete. It is true that the pressure on the dam is light, the maximum depth being only 6 feet, but it is believed that the same construction could be applied to much higher dams with equally good results.

In erecting an electric-light plant for use at Mammoth Hot Springs water power was employed. It became necessary to convey this water for a distance over a depression in the ground, and as the work was to be of permanent character it was decided to put in a concrete flume and aqueduct.

The aqueduct was made in 12-foot lengths, supported upon vertical piers, as shown in the photograph. The various sections united over the piers. The cracks between the sections were closed with sheet lead, after the manner already described in the case of the concrete dam. The results in this case were not quite as satisfactory, owing, undoubtedly, to the fact that less pains was taken to get the mortar around the bends in the sheet lead. However, the aqueduct is practically water-tight, although at first there was some seepage at the joints. For the irrigation of the plateau of about 30 acres at Mammoth Hot Springs it was desired to utilize water from the mains for the domestic supply instead of bringing it in an open ditch. To provide for this extra demand a 10-inch main was laid from the reservoir to the highest part of the grounds to be irrigated. This point where it was desired to release the water was about 100 feet below the level of the reservoir, and it was necessary to adopt some method of reducing the velocity of discharge before letting the water out upon the grounds. It was not desirable to adopt a vertical jet on account of the large quantity of water required and the fact that the wind would scatter it over too wide an area. The following expedient was resorted to: A circular basin, 20 feet in diameter and 4 feet deep, was built of concrete, with a carefully leveled upper edge, consisting of a steel band 6 by inches. The water was expected to flow over the edge of this basin into a circular flume built around it. A 6-inch pipe was led from the main to this basin, so that it would discharge horizontally and tangentially to the circumference at the bottom. The result is that the velocity of discharge is entirely taken up in the basin in the form of a circular motion to the water, which, after the basin is filled, flows over the edge into the flume below, whence it is conducted to the grounds. The experiment was successful so far as the main purpose was concerned, but it has been found that, for the amount of water desired, the basin was somewhat larger than necessary, and therefore the water does not ordinarily flow over it in a full sheet around the entire circumference. It has also been found difficult to secure an even flow all around, as the water sucks down over the end of the discharge pipe and bulges up somewhat at the diametrically opposite point, giving a deeper flow on one side than on the other. Except for these two defects in appearance the result is entirely satisfactory.

All of the above works at Mammoth Hot Springs were executed under the immediate supervision of Mr. Robert Walker, United States

overseer.

Very respectfully, your obedient servant,

Brig. Gen. G. L. GILLESPIE,

H. M. CHITTENDEN, Captain, Corps of Engineers.

Chief of Engineers, U. S. Army.

BBB 20.

[Report of Capt. William W. Harts, Corps of Engineers, on engineer operations in the former Department of North Philippines, and present Department of Luzon, for the period July 1, 1902, to June 6, 1903.a]

HEADQUARTERS DEPARTMENT OF LUZON,
OFFICE OF THE ENGINEER OFFICER,

Manila, P. I., June 6, 1903.

GENERAL: I have the honor to submit the following report of engineer work in the former Department of North Philippines and the present Department of Luzon, for the period July 1, 1902, to date, having been relieved from duty per paragraph 10, General Orders, No. 28, Headquarters Department of Luzon, current series.

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REPAIRS TO ROADS AND BRIDGES.

At the close of the fiscal year 1902 practically all the work in charge of this Office north of the Pasig River had been completed, and with the exception of roads in the vicinity of Manila, for which minor repairs were provided, and the road work in Laguna and Batangas provinces, operations had ended in the territory south of the Pasig.

FIRST ENGINEER DISTRICT.

This district includes the provinces of Cagayan, Isabela, and Nueva Viscaya. The following engineer work was accomplished:

Between Cauayan and Angandanan 1,000 yards of road were repaired, a 50-foot Howe truss bridge was constructed at the Angandanan River crossing, a 50-foot Howe truss bridge was constructed over the Manante River, and an 80-foot trestle bridge over Tagaran River, besides several culverts.

At Cauayan the road from the barracks site to the Rio Grande, 300 yards long, was ditched, graded, and metaled with such material as was at hand.

From the post site at Tumauini to the river landing, 750 yards, an old, neglected road was cleared off, ditched, and reshaped.

About $4,000, Mexican, was expended in the district.

THIRD ENGINEER DISTRICT.

This district includes the provinces of Zambales, Pangasinan, and Benguet. Work was completed about the middle of July, and consisted of the following:

The Pantal bridge across one of the mouths of the Agno River at Dagupan, which was nearly completed during the previous year, was finished by the erection of a 72-foot center span.

At Bayambang a detail of engineer soldiers erected a ferry cable and put the ferry in good running order. Expended $75, Mexican.

a Since which time Capt. Spencer Cosby, Corps of Engineers, has been the engineer officer of the Department.

SIXTH ENGINEER DISTRICT.

The provinces of Rizal, Bulacan, and Cavite compose this district. All work was completed during the previous year, except the repair of the road from the city limits of Manila to Pasay Barracks. All ruts which had developed were filled with stone, ditches were cleared out, and 900 linear yards metaled with gravel. Expended $1,451.51, Mexican.

SEVENTH ENGINEER DISTRICT.

The provinces of Laguna, Batangas, and Tayabas are included in this district. The following work was accomplished:

The road from Calamba to Batangas was completed March 20, having been commenced in October, 1900. Although the work originally contemplated was of an emergency nature, only $150,000, Mexican, having been allotted for the road from Calamba to Nasugbu, distance 80 miles, by means of a subsequent appropriation of the Philippine Commission it was possible to complete a substantial road from Laguna de Bay to Batangas Gulf, 39.5 miles. About 10 miles of the road were built during the current year.

From indications it is probable that a fair road existed where the present one is located. A number of substantial bridges, built some years ago, are still in a good state of preservation, but with this exception and that the grading had to a large part been done, it was necessary to build the road new throughout. In 1899 the old road site was overgrown with vegetation, and mudholes were to be found in frequent succession. The subsoil is of volcanic ashes, and in wet weather it became a mass of sticky mud, through which it was impossible to take wheeled transportation. The first work consisted in clearing and corduroying. As it soon became apparent that temporary work would not suffice for the needs of the Army by reason of the number of garrisons to be supplied and the consequent heavy hauling, it was determined to make the work permanent so far as funds would permit. The fact that garrisons stationed between Batangas and Nasugbu could be supplied with no great difficulty, and therefore extensive road repair not being required between those points, permitted the use of the greater part of the allotment for the Batangas-Calamba end, which amounted, with the funds appropriated by act 311, United States Philippine Commission, to about $240,000, Mexican.

The road as completed is in the following shape: From the Laguna to Calamba, 1 mile, the road is 30 feet wide with a solid rock foundation covered with gravel, and with ample ditches.

Between Calamba and Tanauan the roadway is 16 feet wide, metaled with volcanic tufa 6 inches deep, and covered with 4 inches of gravel or sand or metaled with gravel 6 to 12 inches deep and covered with pit sand. Near Santo Tomas the structure is a 6-inch Telford foundation of volcanic rock, covered with 2 inches of finely pounded disintegrating feldspathic rock with a top dressing of 1 inch of pit sand. The material used here, as elsewhere, was that which was most available. Long hauls and inaccessible quarries prevented anything like uniformity in the road metal used.

From Tanauan to Batangas the character of the metaling varied from a combination of sand and gravel, volcanic tufa and gravel, to a com