straighten the cable spiral lay of conductors and eventually caused a cable break. Two cables on Runit and Engebi and one on the Eberiru tower had to be replaced. One method for solving this problem which has the recommendation of a leading elevator mamufacturing company involves installation of a contimious aluminum gutter from the base of the tower to the top-cab, with its slot facing the elevator cab, The control cable would then be supported from the cab by a bracket extending into the gutter, Cross sectional dimensions would be approximately 6 inches wide by depth sufficient to permit normal loop in cable. Difficulty because of moisture was experienced in the operation and maintenance of the electrical apparatus and controls for the towers. The equipment was specified to be moisture and fungus resistant, and on inspection appeared to be well protected, However, it developed that some parts were not adequately protected and shorts developed when the equipment was installed in the highly humid conditions at the Proving Grounds. This was overcome by installing large electric lights in the building housing the motor-generator set and control panel and maintaining a temperature of 110° F, It is recommended that for future installations the moisture-proofing of equipment be thoroughly tested under conditions of 90° F temperature and 90 per cent relative humidity before shipment and that electric strip heaters be provided for the control and switch panels. The suggestion of an alumimum tower was first presented to Holmes & Narver ina letter from a J-Division representative dated June 28, 1949. The letter was primarily in response to bids received on the 300 foot steel towers but it proposed a contract be made for supplying three all-steel towers and one tower constructed of aluminum to as great extent as possible. Chemistry considerations had made it appear desirable to have one tower with as little steel in it as possible. The condition stated was that steel should not represent more than 10 per cent of the total weight of the tower. The Structural Department made some quick calculations and pre- sented them at a meeting at Los Alamos on July 5, 1949. The use of approximately 21,000 pounds of steel was then approved, except for elevator and hoist guide rails. The steel was all in the lower 25 feet and would not affect the scientific requirement. Approval was given to go ahead with the design and the plans were campleted on September 2, 1949. The lower 25 feet remained identical to the steel 300 foot tower so that the tower could be placed on any of the tower foundations that were being constructed, without modification of the foundations, Aluminum was used for all structural elements above the 25 foot level, even to the use of aluminum structural rib bolts. Until October 18, 1949, the aluminum tower was being negotiated as a part of the order for the steel towers; however, on that date the AEC Engineering Director authorized H & N to put the tower up for separate bids. These bids were received December 7, 1949, and approval on Jamuary 3, 1950, allowed a purchase order to be given to International Derrick and Equipment Co. on January 23, 1951, for their low bid of $47,927.00. 9~139