MANUAL OF TIDE OBSERVATIONS 17 



34. In the old type of gage, the counterpoise drum was mounted 

 directly on one end of the pencil screw and the float drum was then 

 clamped to the counterpoise drum. In the newer instruments with 

 removable pencil screw, the two drums are mounted independently 

 on a short rod, known as the drum shaft^ which turns in ball bearings 

 at each end and is connected with the pencil screw by a slotted 

 joint. Around the middle of the drum shaft is a flange which sep- 

 arates the two drums and contains a pin projecting from both sides 

 which is designed to engage one of a series of holes in the end of 

 each drum. The drums are held against this flange by capstan 

 lock nuts (12, 13, fig. 5), which may be loosened independently to 

 release either drum so that it may be turned when installing a new 

 wire. In the normal operation of the gage these lock nuts are not 

 to be disturbed since any change in the position of the float drum on 

 its shaft will affect the adjustment of the gage. 



35. Wire. — The float and counterpoise drums are designed for use 

 with No. 23 American gage wire which is 0.024 inch in diameter, and 

 wire of this size must be used to preserve the correct scale in the opera- 

 tion of the gage. Formerly a single-strand phosphor-bronze or 

 nickel-chromium wire was used for suspending the float and counter- 

 poise weight, but there is now available a seven-strand staiiiless steel 

 wire containing 18 percent chromium and 8 percent nickel, which is 

 more satisfactory for the purpose. 



36. Float. — The standard float now used for the automatic tide gage 

 has a cylindrical section 8i/^ inches in diameter and 2 inches high with 

 tapering top and bottom sections. Its weight is 414 pounds. Assum- 

 ing the weight of sea water, fresh water, and kerosene to be, respec- 

 tively, 64 pounds, 62.4 pounds, and 55 pounds per cubic foot, the 

 corresponding buoyancy per inch of immersion of the cylindrical sec- 

 tion of the float is 2.10 pounds, 2.05 pounds, and 1.81 pounds, respec- 

 tively. In the normal operation of the gage with a strain of from 12 

 to 16 ounces on the float wire, the float will be approximately one-half 

 submerged. As a free float the immersion will be about one-half inch 

 deeper. 



37. Counterpoise. — The counterpoise acts upon the counterpoise 

 drum to take up the slack in the float wire as the tide rises. Although 

 it may be attached directly to the end of the counterpoise wire, it is 

 preferable to have it act through a movable pulley with the end of the 

 wire fastened to the ceiling of the tide house as this arrangement 

 increases the operating limits of the gage when the height of the ceil- 

 ing is otherwise insufficient to provide for the full range of tide. The 

 weight of the counterpoise together with the operating scale of the 

 gage determines the amount of tension on the float wire. As a tension 

 of 12 to 16 ounces has been found to be generally the most satisfac- 

 tory, the weight should be selected accordingly. The weights recom- 

 mended for use with different size float drums will be found in 

 paragraph 89. 



38. Tension weight. — This weight, acting upon the drum at one 

 end of the receiving roller, serves to wind up the paper on which the 

 record is traced, and, by keeping a tension on the paper, also assists the 

 motor clock in turning the main cylinder. A silk fish line is generally 

 used to connect the weight with the drum. This is called the tension 

 cord. The weight may be either attached directly to the end of the 

 cord or supported from a movable pulley with the end of the cord 



