690 EIGHTH PACIFIC SCIENCE CONGRESS 



was desired further that simple repeating tides could be set up and 

 that a sequence of natural tides could be conveniently interrupted 

 and repeated. 



The tidal harmonic constants computed by the U.S. Coast and 

 Geodetic Survey for Seattle and Port Townsend indicated that a mini- 

 mum of six constituents would be required to reproduce prototype tides 

 within a deviation of ±1 foot. These, the diurnal K^, O^, and P^, and 

 the semidiurnal M,, N^, and So, were incorporated in the tide-generat 

 ing machine using many principles of the Coast Survey's prediction 

 machine. Identical gear ratios were used for corresponding constituents. 

 A 1/3-horsepower motor was used to drive a line shaft through a 

 900: 1 reduction box and spur gears at precisely one revolution in 12 

 solar hours, model time. Scotch yokes, driven from the line shaft by 

 gear trains at speeds corresponding to the period of each constituent, 

 generate cosine functions. These are fed into a summation wire con- 

 nected through a suitable pulley and reduction drum arrangement (Fig. 

 5) to a plunger located in the model headbox. The changing water 

 displacement caused by the motion of the plunger, shaped to correct 

 for the tidal prism, produces the rise and fall of the tides. Phase angles 

 and amplitudes for any epoch or location are readily set for the dif- 

 ferent constituents on the calibrated cranks of the Scotch yokes. A sup- 

 plementary chain drive is incorporated between the Mg and K^ consti- 

 tuents to provide a means of generating repeating tides of either diur- 

 nal, semidiurnal or mixed character. 



River System and Salt Water Addition 



Provision is made for the introduction of fresh water through ele- 

 ven major rivers of the area having a yearly mean discharge ranging 

 from approximately 400 to 16,000 second-feet. The water flows by 

 gravity from a constant head tank, through individual flow meters ol 

 the expanding bed type, to small basins located a short distance up- 

 stream from the river mouths. The rate of flow of the rivers is con- 

 trolled manually by means of individual needle valves. Loss of salt 

 resulting from river runoff is balanced by a circulation system In the 

 headbox. Water is removed from the headbox through a shaped stand- 

 pipe and pumped into a reservoir having a capacity of about 125 liters. 

 Salt solution is added to the water in the reservoir to maintain the 

 desired density. A second pump returns the ^vater from the reservoir 

 to the headbox where it is introduced along the bottom at a rate exact- 

 ly balancing that of removal. In this Avay the net surface outflow from 

 Puget Sound and the balancing infloAv of oceanic water at depth is 

 simulated. 



