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Year.

Amount of Rain and Snow registered at the State Lunatic Hospital, Worcester, Mass., for Twenty-One Years.

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Tide Tables for the Coast of the United States.

PREPARED FROM THE COAST SURVEY OBSERVATIONS BY A. D. BACHE, SUPERINTENDENT.

By the aid of the following tables, the time and foot, and of low waters two feet. (It is consideraheight of the tide at the places named can be ap-bly more in Puget's Sound.) On the west coast of proximately ascertained. To obtain the time of high water on a particular day, add the number of hours and minutes given in the second column of the table to the time of moon's transit or southing on that day, obtained in the astronomical part of the almanac; the sum will be the time required.

On the Pacific coast, and on the western coast of the peninsula of Florida, the heights and times of the morning and afternoon tides differ considerably; the average differences of two consecutive high waters on the Pacific coast being about one

Florida these differences are only about half as much. Rules and tables for the allowance to bo made for these differences are given in the annual reports of the Superintendent of the Coast Survey, but would be too long for insertion in this place.

In the Gulf of Mexico, west of Cape San Blas, the tides ebb and flow as a rule but once in twenty-four hours; being greatest when the moon's declination is greatest, and smallest when the moon's declination is nothing. The heights of the tides on that part of the coast are given in table II.

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THE COAST SURVEY.

officers. Many of the civilians have been trained in the Survey, entering as aids, and rising up by experience and merit to superior grades: these are called upon for duty of every kind. The officers of the army and navy are detailed for temporary

partments,-the navy officers being put in charge of hydrographic vessels, and the army officers employed either in the office or in the land surveys.

THE importance to a great commercial nation, whose domain borders on two vast oceans, of such an institution as the United States Coast Survey, the object of which is the production of accurate charts of our far-reaching coasts and numerous harbors, cannot fail to be appreciated by every in-service, upon application to the Heads of their Detelligent mind. Our Atlantic sea-board is one of the most dangerous in the world; the Florida Reefs are known by repute even to the backwoodsman; the Pacific Ocean rolls its thundering surf against This organization thus avails itself of the spare forbidding, unbroken shores, in warning against forces of the military and naval service of the dangers as yet scarcely discovered. The annual country; and yet when they are called upon for loss to the country by marine disasters is not less their proper professional services the work is not than from fifteen to twenty millions of dollars, entirely suspended, but is continued, on a reduced without mentioning the loss of life,-not to be mea-scale, by the nucleus of civilians. sured by any economical estimate.

To diminish the risks of navigation, and partly to relieve commerce from the tax imposed upon it by such losses, the Coast Survey has been instituted. In connection with an efficient system of light-houses and beacons, accurate charts, with full sailing-directions and notes of dangers, are among the foremost means to that end.

Other maritime nations, such as England and France, have long been engaged in a similar work; and the former, not content with surveying her own coasts and those of her dependencies, has for years prosecuted surveys in all the seas to which her commerce extends.

Although the attention of the United States Government had early been directed to the subject under consideration, the work was not fairly commenced until 1832. It was then taken up under the superintendence of Professor F. R. Hassler, and by him continued until his death in 1843, at which time the completed surveys were comprised between Narragansett Bay and Cape Henlopen, and the publication of charts had just been commenced. His successor, Professor Alexander Dallas Bache, so impressed the Government with a sense of the importance of prosecuting the work on an enlarged scale, that it was soon put in operation on the coasts of all the Atlantic and Gulf States, and, upon the acquisition of Texas and California, was immediately extended to those regions. Under the energetic direction of Professor Bache, the surveys have been prosecuted successfully to the present day, as rapidly as the means provided by Congress from year to year would permit. At present the Atlantic coast is about three-quarters done, and the Gulf coast one-third done; while on the Pacific coast, but lately commenced, all the most essential information has been obtained and published, and a more complete survey is in vigorous progress.

The whole work is under the administrative direction of the Treasury Department. Upon the Superintendent devolves the duty of planning its operations, for the scientific accuracy of which he is responsible. The corps of Assistants is composed of three classes,-civilians, and army and navy

The operations of the Coast Survey are divided into three branches,-the geodetic, topographic, and hydrographic surveys. The geodetic survey accurately determines the relative positions on the surface of the earth of a great number of prominent points, by a system of triangulation and observations of the true meridian lines, and of latitude and longitude. In these operations the true spheroidal figure of the earth must be taken into account, and the most refined methods of practical science and astronomy are brought into requisition. For such a sketch of these operations as would be intelligible to the general reader our pages afford no room; but it may be said that American science is acknowledged to have improved on former methods in nearly every department; and in the determination of longitude by means of the electric telegraph the Coast Survey has taken and kept the lead of all similar undertakings. The positions fixed by the triangulation form the ground-work of the topographic survey which delineates the shore-line of the coasts, bays, and rivers, the shape and heights of hills, roads, houses, woods, marshes, and fields,-in short, all noteworthy features of the country. This is done by means of an instrument called the plane-table, with which a reduced drawing from nature is made on a map on which the triangulation points have been previously laid down in their true relative positions, according to the scale used, serving as checks against the accumulation of small errors. These topographical maps are generally made on a scale of one ten-thousandth, or about six inches to the mile.

Next in order, and based upon the points and shore-lines furnished by the triangulation and topography, comes the hydrographic survey, which, by a thorough system of soundings, delineates the hidden configuration of the sea-bottom, discovers channels, shoals, and rocks, assigns their true positions, and shows the depth of water and character of the bottom over the whole extent of the chart.

As the depth of water varies with the tide, all the soundings are referred to average or mean low water, for which purpose observations of the tides

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