16 U. S. COAST AND GEODETIC SURVEY 



it is connected with the drum shaft by a slotted joint and at the 

 other end is held in place by a capstan bearing pin (45, fig. 9). By 

 backing off this bearing pin the pencil screw is easily released so that 

 it may be lifted out. 



30. Recording pencil. — The recording pencil (37, fig. 7) traces the 

 tide curve. This pencil is secured in its holder (38) by a clamping 

 screw (39). The gage is provided with a special automatic pencil 

 but any ordinary pencil with a medium soft lead can be used for 

 the purpose. The holder is secured to the pencil arm (41) by two 

 pivot screws (44) which permit a small lateral movement for striking 

 the hour marks. One pivot screw is clamped by a lock screw (46). 

 In the bearing of the pencil arm there is a pin screw (43) which fits 

 into the thread of the pencil screw, and as the latter is rotated 

 through the action of the tide, the pencil arm is moved toward the 

 clock unit or away from the same according to whether the tide is 

 rising or falling. 



31. Datum pencil. — The datum pencil (24, fig. 7), which draws the 

 datum line from which the record is scaled, is similar to the recording 

 pencil. Its holder is secured to the rod (20) by a clamp (21). This 

 clamp consists of a split block held together by two screws. One of 

 the screws is covered by the spring attached to the holder and must 

 be tightened before the spring is placed in position. The other screw 

 is secured by the clamping nut (22) after the holder has been ad 

 justed to the position desired. 



32. Hour-marking device. — The hour-marking device is actuated 

 by the time clock. A cam attached to the main shaft of the clock 

 turns with the minute hand and operates a lever which is connected 

 with a small arm (33, fig. 9) projecting from the back of the clock 

 case. This arm presses against a spring (31) attached to the striker 

 weight (29, fig. 8). The latter is secured by a binding screw (30) 

 to a rod that actuates the tripping rod (26). Beginning 30 minutes 

 before the time for striking the hour, the cam in the clock gradually 

 swings the small arm upward, raising the striker weight and moving 

 the tripping rod in toward the recording pencil. On the exact hour 

 the cam suddenly releases this arm, thus causing the weight to fall 

 and the rod to move suddenly outward. The latter strikes the end of 

 the hour-tripping hook (36) attached to the pencil holder, causing 

 the pencil to make a short hour mark parallel to the edge of the 

 paper. Through the action of the pencil weight (42) the pencil is 

 then immediately returned to its original position. 



33. Float and counterpoise drums. — The -float drum (11, fig. 5), 

 which operates the pencil screw, is threaded to accommodate the 

 wire to which the float is attached. The counterpoise drum (10) is 

 similarly threaded for the wire to the counterpoise. A small hole 

 or a clamp near one edge of each drum affords a means for attaching 

 the wire. The drums* now in use are either 1% or 1% inches wide. 

 As the threads are cut 16 turns to the inch, the narrower drums 

 will accommodate 18 turns of wire and the larger ones 28 turns. 

 To provide suitable recording scales for different tidal ranges, inter- 

 changeable float drums of different sizes may be used. Those now 

 available have circumferences of 6, 9, 12, 16, and 24 inches. The 

 counterpoise drum is 6 inches in circumference for all scales. The 

 wiring on the two drums is so arranged that one winds as the other 

 unwinds. 



