HARMONIC ANALYSIS AND PREDICTION OF TIDES. 137 



setting the new amplitudes if the gear changes are in the order of 

 2:1, 3:2, 1:1, and after setting the amphtudes if the gear changes 

 are in the reverse order. This precaution will lessen the chances of 

 jambing the curve pen carriage and throwing the height chain off its 

 pulleys when setting the amplitudes. 



Inserting paper roll. — To place the paper on the machine, remove 

 the mandril that is mounted within the dial case near the upper 

 right-hand corner and slip the roll of paper over the mandril, the 

 roll being so placed that the winding is clockwise when viewed 

 from above and when on the machine the paper unwinds from the 

 outer side of the roll. In placing the roll on the mandril care should 

 be taken to see that the small projection on the base of the latter 

 enters the cavity in the wooden core, so that the roll will fit flat 

 against the base. After the mandril with the roll of paper has been 

 returned to the machine and secured in place the end of the paper 

 is passed around a roller to the face of the machine, across the face, 

 and over the feed roller at the left of the machine. The end is then 

 inserted into the slit in the receiving roller, which is given a few 

 turns to take up the slack paper and make it secure. Before passing 

 the paper over the feeding roller and on the receiving roller these 

 rollers should be released to permit them to turn independently, the 

 release being effected by turning the small milled head on a ratchet 

 stud gear near the base of the feeding roller and by lifting off from 

 the top of the receiving roller the small knob holding the connecting 

 chain. After the paper has been secured to the receiving roller these 

 connections should be restored. 



Curve pen adjustment. — With the machine in its mean sea-level 

 position, the curve pen must be adjusted to bring the pen point on 

 the mean sea-level line as drawn by the base-line pen. This adjust- 

 ment may be effected by releasing the pen carriage from the oper- 

 ating chain and moving it to the desired position, where it is clamped 

 in place by the binding screw. 



Verification of machine settings. — Each step in the adjustment and 

 setting of the machine should be carefully checked before proceeding 

 with the next step. After the setting of the machine for any station 

 has been completed an excellent check on the work is afforded, if the 

 predictions for the same station for the preceding year are available, 

 by turning the machine backward several days and then comparing 

 the predicted tides with those previously obtained. 



Predicting. — The datum and curve fountain pens are filled and put 

 in place, the electric cut-out switch under the base of the machine 

 closed, and the ratchet of the operating crank set to prevent the 

 machine from being turned backward. 



If the predicted height of the tide for any given time is desired, 

 the machine may be turned forward until the required time is regis- 

 tered on the time dials and the corresponding height read off of the 

 height dial. 



If the predicted high and low waters for the 57-ear are desired, the 

 operating crank is turned forward until the machine is automatically 

 stopped by the brake at a high or low water. To avoid the strain 

 on the machine due to sudden stops, the operator should watch the 

 small index on the time chain, and as this approaches the fixed index 

 in the center of the opening on the face of the machine, turn the 

 crank more slowly until the machine is stopped as the indexes come 



