HAEMONIC ANALYSIS AND PREDICTION OF TIDES. 



133 



receiving roller to wind up all the paper delivered by the feed roller, 

 the tension on the paper being kept uniform by the friction device. 

 To remove a completed roll of record the smaller sprocket is lifted 

 from the receiving roller and a pin {39, fig. 16) at the back of the dial 

 case is drawn out, releasing the upper bearing bracket. The bracket 

 can then be raised and the receiving roller with its record removed. 

 A similar bracket secured by a pin is provided for the removal of the 

 mandrel on which the blank roll of paper is placed. 



Marigram gears. — The pen that traces the tide curve is mounted 

 in a carriage which is arranged to slide vertically on a pair of guiding 

 rods and is controlled from a horizontal shaft at the back of the dial 

 case. On this shaft there is mounted a set of three sliding change 

 gears {18, fig. 17), which are designed to mesh, respectively, with 

 three fixed gears mounted on a shaft just above. By sliding the 

 change gears in different positions any one of them may be brought 

 into mesh with its corresponding fixed gear. These gears provide 

 for ratios of 1 : 1, 2 : 1, and 3:2, according to whether the innermost, 

 the middle, or the outer gears are in mesh. At the outer end of the 

 shaft containing the fixed gears is a thread-grooved wheel 4 inches 

 in circumference {19, fig. 17), to which is attached one end of the 

 pen-carriage chain {20, fig. 17). The chain is partly wound upon the 

 wheel and from it passes through the dial case to the front of the 

 machine, then upward over a pulley near the top to a counterpoise 

 weight within the dial case. The pen carriage is secured to this chain 

 by means of a clamp and can be adjusted to any desired position. 



Scale of tide curve. — With a working scale of unity the arrange- 

 ment is such that the motion of the height summation wheel as 

 transmitted to the curve-line pen through the marigram gears with 

 ratio of 1 : 1 causes the pen to move vertically 0.1 inch for each unit 

 change in the predicted height of the tide. If the marigram gears 

 with ratio 3 : 2.or 2 : 1 are used the unit of height will be represented 

 by a vertical movement of the pen of 0.15 or 0.2 inch, respectively. 

 For any working scale other than unity the above unit equivalents 

 must be multiplied by the number representing that scale. 



The scale ratio of the tide curve will depend upon the unit of height 

 used for the predictions. Taking the foot as the unit, the following 

 scale ratios are obtained: 



Pens. — The curve-line pen {13, fig. 12) and the datum-line pen 

 {IJf) are each of the ordinary fountain type. Each is fitted with a 

 metal lock joint, so that it may be quickly removed and replaced in 

 the same position, and is pressed against the paper by a light coil 

 spring when in use. The curve-line pen is mounted in a swivel arm 

 on a light carriage which slides vertically along two rods. The datum- 

 line pen is mounted in a swivel arm that may be adjusted so that the 

 mean sea-level line will be traced midway between the upper and 

 lower edges of the paper. 



