4. The United States Tide Predicting Machine No. 2
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This image shows the business end of the United States Tide Predicting Machine No. 2. This machine was built in 1910 and went into service in 1912. Built on the same principles as Kelvin's machine, it was a double machine, with one side summing the heights of 37 tidal constituents, and the other side summing their derivatives, so it could give both the height of the tide and the exact times (when the sum of the derivatives went through zero) of stationary points, including high and low tides. This machine still resides in the lobby of NOAA Headquarters in Silver Springs MD. It was used until 1966 to generate the official US tide tables. Image from NOAA/NOS CO-OPS Tide Predicting Machines page, where more information is available.
Setting the amplitude and phase of a tidal constituent. This photograph, from NOAA/NOS shows the linkage between the gears and the pulleys, the up-and-down alternatio of the constituents, and the wire linking the pulleys.
Running the machine and recording the data. Note the operator's left hand: the machine was hand-cranked until 1961. Image (1944) from NOAA Historical Photo Collection, credit: Association of Commissioned Officers.