ficient elevation above the elevation of lower sill, so that it would be only necessary to raise the crest when the stage of water is fairly low, as a foot or two passing over the dam, or where most of the surplus water can be passed through the draining valves.

Lieut. L. M. ADAMS

Corps of Engineers

After looking over the copies of the discussions of the movable top described in the article, it would appear that too much consideration and weight has been given to the well known obstruction and failure of the A-frame dam which was installed as a movable weir at Dam No. 6, Ohio River, in 1899-1900. It should be borne in mind that the article describes a movable top to a fairly high fixed dam in contradistinction to an A-frame movable dam seated deep in the bed of a swiftly flowing river. Furthermore, the movable top was proposed for a particular stream, the Monongahela, which carries but a small amount of sediment in suspension and but very little floating drift even in time of high water, in which condition the movable top is down in its recess and entirely protected from obstruction. It was assumed from the first that the recess along the crest of the fixed dam would accumulate considerable very soft fine silt in the same way that the recesses for the gate machinery of the locks accumulate silt, but no trouble from this source in operating the movable top is anticipated, inasmuch as the fine silt in the gate-machinery recesses gives little or no trouble. No sand or gravel is ever found in these recesses.

The lock-master at Dam No. 6, Ohio River, Mr. R. C. McCullough, gave me a very clear written report on the failure of the 120-foot A-frame movable dam at this work, and I shall quote briefly from it:

"There was a bar where the A-frame weir was built, which had to be removed, and it was also necessary to remove some of the bank, as you understand the weir is next to the shore. The bar reformed after the cofferdam was removed and at the present time is about even with the crest (standing position) of the A-frames on both upper and lower sides. The gravel and sand is banked up against the frames on both sides. The weir was never operated since the cofferdam was removed, and the openings beneath the A-frames are also filled with gravel. There is an eddy on the weir side of the river at all stages and everything seems to collect there, as we find from 2 to 3 feet of gravel every spring on the bear-trap leaves which are next to the A-frame weir.

From this report of conditions at Dam No. 6, Ohio River, it would seem unreasonable to condemn the A-frame principle for all locations and special applications. It would seem from the discussions preceding that at least a few features of the design for which originality might be claimed have been overlooked; that is, reducing the ratio of height to width of frames by one-half and thereby reducing the number of frames and accompanying mov

able parts by one-half for the same length of dam; also, the eccentric loading of the frames so that they seat themselves by gravity in the last movement to the standing position; also, the large hatchet-shaped pawl to afford positive means of locking and unlocking the operating chain; also, the design of the last counterweighted abutment frame to maintain tension on the operating chain and thereby afford an automatic start in the operation of lowering the movable top as soon as the chain is slackened from the lock wall; and again, the design of the crest of the fixed dam to carry the movable top in the down position with a minimum depth of 1 foot of water above it for protection.

A NEW PORTABLE SEARCHLIGHT TOWER

BY

Lieut. W. H. ROSE
Corps of Engineers

In connection with the description of the German portable telescoping tower, published with illustrations in the article on "Field Searchlights" in the last number of the MEMOIRS, a recent development in this line may be of interest.

The manufacturer of the tower above referred to has recently put on the market an ingenious modification in which a three-part tubular mast is substituted for the wooden framework of the older type. The tubes telescope inside each other in the same manner as the sections of the wooden tower. The telescope mast lies in a horizontal position for transport, and can be erected in a vertical position previous to extending by rotating it around an axle mounted behind and above the rear axle of the carriage. The extension is secured by simple apparatus operating on the same principle as that described in connection with the wooden tower.

The upper section of the mast carries on its upper extremity a pressed sheet-steel fork with holes for the trunnions of the projector drum. For projectors up to 90 centimeters in diameter a single mast is used; for larger sizes a double mast with a cross-arm connection at the top supporting the projector. The single mast type is made from 7 to 9 meters in height and the double mast about 5.4 meters.

For the single mast it is claimed that the erection, adjustment, and extension can be effected by two or three men within two minutes, and that the reduction requires not more than fifteen seconds.

The masts are mounted on turn tables so that they can be revolved in azimuth, and the projector can also be turned in its trunnions. These movements can be effected either by hand or by electric motors.

SELECTED ARTICLES OF ENGINEERING INTEREST

Compiled by Henry E. Haferkorn, Librarian, Engineer School.

In the lists of selected articles published, the publication is referred to by the number preceding its title in the following list. The following abbreviations will be used: I, for illustrated; D, for diagrams.

|(29) Transactions, American Society of Civil

Engineers.

(30) Professional Memoirs, Corps of Engi

neers.

(31) Journal of the Royal Artillery (Wool wich, England).

(32) Royal Engineers' Journal (Chatham, England).

(33) Proceedings Brooklyn Engineers' Club. (34) Concrete.

(35) Bulletin de la Presse et de la Bibliographie militaire (Brussels).

(36) Internationale Revue ueber die gesamten Armeen und Flotten (German and French). (Dresden.)

(37) Revue d'Artillerie (Paris).

(38) Kriegstechnische Zeitschrift (Berlin). (39) The Contractor.

(40) Cement Era.

(18) Journal of Western Society of Engi|(41) Canal Record (Ancon, C. Z.).

neers.

(19) Journal of Franklin Institute.

(42) Proceedings, Engineers' Society of Western Pennsylvan ́a.

(20) Journal of Royal United Service Insti (43) Journal, United States Artillery. tution (London).

(21) Proceedings, American Society of Civi Engineers.

(22) Proceedings, Engineers' Club of Philadelphia.

(23) Municipal Engineering.

(24) Municipal Journal and Engineer,

(25) Railway Age Gazette.

(44) Transactions, Society of Engineers

(London).

(45) Journal, Association of Engineering Societies.

(46) United States Naval Institute. Proceedings.

(47) Revue du Genie Militaire (Paris). (46) La Technique Moderne (Paris).

(26) Revue Generale des Chemins de Fer (49) Electrical World.

(50) Electrical Review (Chicago).

(51) Journal, Military Service Institution. (52) Barge Canal Bulletin.

The Krupp Works. C. Van Langendonck. (13), March, 1911. I. The works of John Cockerill, Seraing, Belgium. (10), Dec. 23, 1910.

BARGES.

Concrete barges for the Panama Canal. M. E. Rupp. Petrol-driven oil tank barge. (10), Feb. 19, 1911. D. I.

BREAKWATERS.

(40), Feb., 1911. I.

Methods and cost of constructing stone filled timber breakwater, Lincoln Park extension, Chicago. (12), Feb. 22, 1911. D.

CAISSONS.

Caisson for the new Quebec bridge. (10), Jan. 6, 1911. I.