20 U. S. COAST AND GEODETIC SURVEY 



42. Record cylinder. — The record cylinder (3, fig, 11) on which 

 the paper for the record- is wound is 7 inches in length and 19.2 

 inches in circumference. The cylinder is geared to a clock movement 

 carried within itself which causes it to rotate on an axle through its 

 center. The axle is clamped in its supports by a capstan nut (4, fig. 



11) and the cylinder should be so placed that this nut is on the same 

 side of the instrument as the train of gear wheels. In 4:his position 

 the cylinder rotates in such a direction that the top moves towards 

 the stylus screw. The cylinder is provided with a clip (24, fig. 12) 

 for holding the record paper in place. 



43. Clock movement. — An 8-day clock movement is mounted inside 

 the record cylinder, its function being to rotate the cylinder at a 

 uniform rate, which is once in 48 hours. The circumference of the 

 cylinder moves forward 0.4 inch per hour, the time scale of the 

 record. Keyholes for winding and regulating are in the end of the 

 cylinder containing the clamping nut. 



44. Stylus screw. — The stylus screw (21, fig. 12) is actuated by a 

 train of gears connecting with the float drum and operates the arm 

 that carries the recording stylus, moving this arm backward and 

 forward as the tide rises and falls. The screw is made of phosphor 

 bronze and has a square screw thread with a pitch of 0.4 inch. The 

 screw thread terminates in circular grooves at each end to prevent 

 the stylus arm from jamming when the limit of its movement is 

 reached, and springs (23, fig. 12) are provided to force the arm back 

 again on the thread when the tide reverses. A gear wheel (6, fig. 11) 

 is clamped to one end of the screw by a milled-head nut (7, fig. 11) 

 and may be released when it is desired to reset the stylus. 



45. Stylus arm. — The stylus arm (33, fig. 13), which carries the 

 recording stylus, has in its bearing a pin that fits into the thread of 

 the stylus screw and when the latter is turned with the rising and 

 falling of the tide the arm moves backward and forward along the 

 screw. The stylus arm carried a small weight (37, fig. 13) to over- 

 come the tendency to be thrown back on a rising tide. A stylus 

 holder (35, fig. 13) is pivoted to the arm. Two slow-motion screws 

 act upon this holder — one (34, fig. 13) is designed for a refined time 

 setting of the stylus, and the other (25, fig. 12) is designed to set the 

 stylus to an exact height reading. 



46. Recording stylus* — The recording stylus (36, fig. 13) consists 

 of a pointed blade, designed to trace the record on a specially prepared 

 wax-coated paper. The stylus is so shaped that it will ride smoothly 

 over the clip that holds the paper in place. In some of the older 

 type^ of the gage, ordinary pencils and special chronograph pens have 

 been used, neither of which proved entirely satisfactory. Special 

 difficulties arose in the use of ink in the chronograph pen because of 

 the excessive dampness to which the record paper is often exposed at 

 the tide stations. 



47. Float drum. — The float drum (17, fig. 12) is 12 inches in cir- 

 cumference and about 1 inch wide with the face threaded to accom- 

 modate 30 turns of the float wire. The drum, together with its 

 oil-tight cover (31, fig. 13), forms a housing for the counterpoise 

 spring. The drum is rigidly fastened by means of a screw (18, fig. 



12) to that part of its axle (19, fig. 12) connected with the gear wheel. 



