SCIENCE SIFTINGS

New Zealand Tablet, 19 April 1917, Page 49

SCIENCE SIFTINGS

By ‘Volt.’

iviysterious Tide Machine has Written a Book. In Washington (says the New York Times) there is a machine that is a mechanical prophet. It foretells the tides all over the world. Every ship entering every port in the world has on board a table of tides. The captain can show you where it will be high tide in every leading port of the world every day in the coming year. How are the facts found out ? That is the job of the predicting tide machine, invented, constructed, and operated in the office of the United States Coast and Geodetic Survey. Fifteen years were required for perfection of the apparatus. There is in the world only one machine of the kind. A second one not so good is in the service of t lie British Government.

The volume of tide tables just issued for the tides of the world iij 1917 contains 488 pages and includes predictions for all tides at 78 selected ports, and tidal differences for 3000 stations. Full tide predictions are given for seven new ports—East port. Me; Albany, N.Y. : Delaware Breakwater, Delaware (using differences from Sandy Hook) Humboldt Bay, California, and Juneau, 'Seldovia, and Apokak, Alaska. The tables are of octavo size, and the time is given as a.in. and pan., with the latter printed in heavy-faced type. There are not many accountants who can calculate simultaneously from ten factors and give a result at once. This machine calculates simultaneously from 37 factors and gives the result on paper on the turn of a crank. It makes a drawing which shows the result on the turn of a crank. Furthermore, some of these results are averages of variables. They include also such forces as the attraction of the sun, the attraction of the moon, the density of (he earth, and a few other simple matters of that sort. By reason of the tested accuracy of the results of this machine one enters

with a feeling of perfect safety on a voyage (o a dis taut port.

A few days ago the machine told one visitor that the United .States Coast and Goedetic Survey was working on the tides for the Harbor of Bombay for the afternoon of October 15, 1918. It does not make the least difference to the machine whether the information desired is for 1918 or 1958. It is just as easy for it to work 100 years hence as it is to work two years hence.

Dials on the face of the machine show the height of the tide, the hour and minute of time, and the day of the month for the year for which predictions are being obtained. While the machine will give the height of the tide for any hour, the figures that are desired for the tide tables are the time and height of high tide and low tide. Whenever the sum of the components is a maximum or minimum—that is, whenever it is high or low tidea most ingenious device, operated by an electric magnet, stops the machine at the proper point, and the operator notes down the hour and (lie minute indicated by the time dial and the height of the tide shown on the height dial, the operation being continued until the desired year is tabulated. At the same time a moving fountain pen draws on a turning roll of paper a curve of the tide. In these ways the machine turns out in from ten to fifteen ‘hours the work that would keep a mere human calculator busy for six months.

The brass brain that performs these wonders weighs 25001 b. Like the vitals of a giant clock it. stands in one of the rooms of the Coast and Geodetic Survey, in Washington. The mechanical tide computer is 11 feet long, but only two feet wide, and stands as high as a man. It -is a seeming jumble of shafts, cams, sliding plates, pulleys, and chains, but each of the elements stands carefully in place as a very tangible representative of . a far-away force of the sun and moon and registers figures that indicate the pull which, months

in the future, will result in the rise of millions of tons of water perhaps thousands of miles away. In 1872 Sir William Thompson (later Lord Kelvin) made a rough model for showing the feasibility of predicting tides mechanically, and since that time several tide-predicting machines have been made. In 1882 the Coast Survey made its first predicting machine, which was used for a number, of years. This machine, however, as well as the others, left a great deal to be desired.

Befoie predictions for a port can be obtained the results of tidal observations taken have to be analysed by what is known as harmonic analysis, devised by Sir William Thompson in 1867. This analyses the tide and divides it up into a number of components. These components represent the forces acting on the tides, such as the attraction of the moon, the attraction of the sun, and a few other matters of the sort. A Government book, written in as peculiar a way, perhaps, as any modern publication, is the object of constant reference by* hundreds of navigators, engineers, hydrographers and other scientists, not only in the United States, but in all parts of the world. It is the annual volume of Tide Tables , issued by the Coast and Geodetic Survey that is literally ground out of (his machine. The book consists of tables of closely printed figures showing, to those who understand such matters, the exact hour and minute of each day for the calendar year when the tide will rise to its crest and sink to its lowest depth in all important ports that arc bathed by the seas.