132 U. S. COAST AND GEODETIC SUR\TEY, 



the operator has noted the time and height readings of the high or 

 low water he may easily break the circuit at the crank hub by a slight 

 inward pressure against the crank handle, thus releasing the arma- 

 ture and pawl and permitting the machine to be turned forward to 

 the next stop. By means of a small switch (23, fig. 15) just below the 

 crank the circuit may be held open to prevent the automatic device 

 from operating when so desired. 



Nonreversing ratchet. — Upon the crank shaft, close to the bearing 

 in the desk frame, there is a small ratchet wheel and above this there 

 is a pawl (24, fig. 15) that is lifted away from the wheel by friction 

 springs when the machine is being turned forward but which is 

 instantly thrown into engagement when the crank is accidentally 

 turned backward. By pushing in one of the small buttons {23, fig. 15) 

 just above the crank the pawl is locked so that it can not engage the 

 ratchet, thus permitting the machine to be turned backward when 

 desired. Pressure on another button releases the pawl. 



Tide curve. — The tide curve which graphically represents the rise 

 and fall of the predicted tide is automatically traced on a roll of 

 paper by the machine at the same time that the results are being 

 indicated on the dials. The curve is the resultant of a horizontal 

 movement of the paper, corresponding to the passing of time, and a 

 vertical movement of a fountain pen (i^,fig .12), corresponding to the 

 rise and fall of the tide. The paper is 6 inches wide with about 380 

 feet to the roll, which is sufficient to include a little more than a full 

 year of record of the predicted tides at a station. The paper should 

 be about 0.0024 inch thick in order that the complete roll may be of 

 a suitable size for use in the machine. 



Within the dial case, near the upper right-hand corner, is a mandrel 

 (83, fig. 16), which can be quickly removed and replaced. It is 

 designed to hold the blank roll of paper, the latter being wound upon 

 a wooden core especially designed to fit on the mandrel. At the 

 bottom of the mandrel is an adjustable friction device to provide 

 tension on the paper. From the blank roll the paper is led over an 

 idler roller {34-, fig. 16), mounted in the front plate of the dial case, 

 then across the face of the machine for a distance of about 13 inches 

 to a feed roller {35, fig. 16), then over the feed roller to the receiving 

 roller {36, fig. 16), upon which it is wound. 



The feed roller governs the motion of the paper across the face of 

 the machine and is provided near each end with 12 fine needle points 

 to prevent the paper from slipping. The feed roller is controlled 

 by the main vertical shaft of the dial case through gearing of such 

 ratio that the feed roller will turn at the same rate as the main 

 vertical shaft; that is to say, one complete turn of the feed roller 

 will represent 12 dial hours in time. The feed roller being 6 inches 

 in circumference the paper will be moved forward at the rate of 

 one-half inch to the dial hour. A ratchet and pawl (57, fig. 16) are 

 so placed as to leave the paper at rest when the machine is turned 

 backward. If desired, the paper feed can be thrown out of action 

 altogether by turning a small milled head on the ratchet gear. 



To provide for the winding up of the paper on the receiving roller 

 there is a sprocket wheel {38, fig. 16) held by adjustable friction to 

 the upper end of the feed roller. Fitted to the top of the receiving 

 roller is a smaller sprocket which is driven by a chain from the feed- 

 roller sprocket. The ratio of the sprockets is such as to force the 



