MANUAL OF TIDE OBSERVATIONS 57 



stake three sharpened poles of suitable length may be driven about 

 6 or 8 feet apart and the upper ends brought together and lashed in 

 the form of a tripod, the float pipe being lashed in a vertical position 

 to the apex of the tripod. 



184. Attaching float. — When installing the instrument on the float 

 pipe the first step is the attaching of the float. The length of wire 

 required may be determined as follows : 



Let J. = distance in feet of float drum to water surface. (Actual 

 measurement not necessary.) 



Let ^= height in feet of tide above or below approximate mean tide 

 level. 



In the formula below use plus ( + ) B ii tide at the time is above 

 mean tide level and minus ( — ) ^ if below mean tide level. 



Length of wire required=-4-i-15 feet ±5, 



Take a spool of wire and attach one end of the wire to the float 

 and lower it into the well. Allowing a few inches for the distance 

 from the top of the well to the float-wire drum, measure off an addi- 

 tional length equal to 15 feet ±5, the value of B being estimated from 

 the stage of the tide, and then cut the wire. Pass the loose end of the 

 wire over the fixed fair leader and through the opening in the 

 base of the instrument, and then before attaching the wire to the 

 drum wind up the spring either by turning the drum counterclock- 

 wise, as viewed from the side shown in figure 13, or by use of the 

 clock key on the drum axle (30, fig. 13). The spring should be 

 wound up completely and then slackened off about four turns. Hold- 

 ing the drum in this position, the float wire is now passed through 

 the small drill hole near the edge of the drum and knotted. The 

 drum should now be permitted to turn slowly through the action 

 of the spring, winding up the float wire, care being taken that the 

 wire follows the threads in the face of the drum. When all the 

 slack in the wire has been taken up the gage is placed in position 

 on top of the float pipe and locked by means of the two anchor 

 hooks (27, fig. 13). 



185. Counterpoise spring. — If the float wire has been cut off at the 

 proper length and the instructions described in the preceding para- 

 graph followed the counterpoise spring will be wound to the proper 

 tension ; but if further adjustment to the tension is necessary this may 

 be made by using the clock key on the subsidiary axle (30, fig. 13) of 

 the float drum. 



186. Gear train. — Having determined the scale of the record to be 

 employed from a knowledge of the approximate range of tide at the 

 station, the proper gears for the float-drum axle and the stylus screw 

 corresponding to that scale are given in the table on page 23. The 

 gears to be used are also printed on the cross-section record paper for 

 each scale. The number of teeth is stamped in each gear and care 

 must be taken in selecting and installing the correct gears corre- 

 sponding to the scale used. 



187. Although the same idle gear (8, fig. 11) is used for all scales, 

 its position varies with the different gear combinations. When chang- 

 ing the gears the idler must be removed, and after the other gears 

 have been installed, it is replaced, being secured by the gear screw 

 (9, fig. 11) in the particular hole provided for the combination. The 

 lever nut (10, fig. 11) provides a convenient means for loosening or 

 tightening the gear screw securing the idle gear. The gears attached 



