the force of gravitation upon itself, thereby diminishes the centripetal and multiplies the centrifugal action of the neighbouring planets. The wise economy exercised in the framework of the planetary system is here apparent, as the planets are continually engaged in withdrawing an excess of pressure from each other, which might prove obstructive to the organic scheme, and either lead to partial disorders or a state of universal chaos. Whilst the moon is therefore revolving around the earth, and conservating more wise ordinations in physics than we are able to comprehend, by weakening the force of centripetal action on particular parts of the earth, and restoring it by turns, are we indebted for the leading phenomena of tides.

In estimating the influence of tidal laws on the deposition of marine and fluviatile alluvian in estuaries of the sea, by tracing the action and the effect of the tide-wave, are we to deduce the causes of some bays silting up, while others remain deep water to the very rocks which determine their boundaries. The laws of fluidity may be here traced out, whether applied to the universe, to the globe in general, or to particular portions of its surface, as the chief operating cause in the means of organic action.

To observe how these laws work on the shores of Great Britain, due notice must be taken of the several incidents that belong to neighbouring oceans, seas, and estuaries. The Baltic Sea has neither ebb nor flow of tide; and a

current continually sets into the North Sea through the Sound. The Baltic is therefore unconnected with the tide-wave of the North Sea. The average depth of water in the former sea may be taken at from 25 to 35 fathoms, and its greatest depth scarcely exceeds 100 fathoms. Its shores are seldom covered by water which exceeds 25 fathoms, and they are comparatively regular in depth and shallowness of water.

Deduced from these incidents, the Baltic would appear to have been considerably silted up in the early periods of the earth's formation; and that it now remains a great inland drain to the plain of eastern Europe. It might have otherwise been expected to be dry land, and covered by early depositions, the same as the adjacent plains. The numerous lakes indeed which exist between the Gulf of Finland and the White Sea, would seem to indicate depositions too imperfect to become continuous dry land. As this great continental drain meets the tide-wave of the North Sea on the southern shore of Norway, and as inland streams supply an elevation of water, which balance the intermitting flow and ebb of tides on its entrance into the North Sea, so these tides effect no perceptible difference in the general elevation of the waters of the Baltic; and the area appears to be too limited and shallow for lunar influence to act upon.

Bearing as these incidents do upon each other,

The

it may be inferred that but little of the earthy materials borne into the Baltic by inland streams is carried through the Sound, and partly drifted only upon its shores. An opinion moreover prevails that the waters of the Baltic are slowly receding from the land, or drifting up by repeated depositions of upland silt. This is undeniably true. Commercial Gazette of St. Petersburgh, of the 28th of May, 1834, contained the following notice on the level of the Baltic. "It has been remarked that, during the last twenty years, the water of this port has been considerably lowered, and affords a new proof of the correctness of the observations made by the ancient inhabitants of the shores of the Baltic, that the bottom of the sea continually rising, the level and body of the water is continually diminishing, and that the land is increasing on every side. According to the researches of the ancient naturalists, phenomena of this sort mostly occur in countries near the North Pole. We can quote as examples the lakes of Denmark, which have sunk so low that some of them are almost entirely without water. Sweden and Norway 2500 years ago formed one island. The town of Pittea, in 45 years became distant from the sea two miles, and the water receded from Loulea one mile in 28 years. The ancient port of Lodisa is now four miles from the sea, and that of Westerwich two miles. At the time of the foundation of Torneo, large vessels could come up close to it; now it is

in the middle of the peninsula. The island of Errgsoe and Curoe, Apsoe and Testeroe have been for many years joined to each other; and Louesoe, Psalmodi, Magdelone, and many more have become part of the main land. It was upon these facts, connected with other observations, that Terinæus and Celsius concluded that the depth of the Baltic Sea diminished four inches in every century, and that in 2000 years it would entirely disappear. Although more accurate observations made in modern times do not confirm the diminution to be so rapid as this, they concur with the generally received opinion that the bottom of the sea in the northern ocean rises in a degree, though the level of the water does not sink. It is difficult to decide which two of those opinions is most correct; but it is incontestable that the main land washed by the Baltic is enlarging; that the rivers and lakes are diminishing in depth; that banks are forming in the sea ports; and that sooner or later the inhabitants of the shores of this sea will be driven to dig canals, and perhaps to lay down iron railroads in order to maintain their commerce."

The former has a

The space and depth of water in the Mediterranean Sea exceed the Baltic. trifling ebb and flow of tide.

But like the latter

it is separated in its action from the main body of the ocean. From these facts we learn that neither the North Sea, St. George's Channel, nor the Bristol Channel, limited in space and depth of

water as they are, contain within their several boundaries the causes which regulate the flow and ebb of tides. So far the withdrawal of atomic pressure, or the mystic term of the attraction of gravitation, or augmented atomic pressure, by lunar influence and centripetal action, or centrifugal repulsion, do not apply in any perceptible ratio. The causes which originate and determine tidal phenomena upon our shores must therefore be sought for extraneously. In spaces so enlarged and waters so deep as the Atlantic Ocean and the Polar Sea, which may be regarded as one continuous body of water, the loss and gain from either centripetal or centrifugal action by especial lunar influence on the fluids of the planetary system, become wonderfully active and organic in their results. It is true, what may be denominated irregularities prevail. These, however, may be distinctly traced to corresponding incidents which are apparent on the figure and features of the globe, broken as its face is into oceans, seas, and estuaries, together with the difference of curvature pervading each parallel of the earth's surface. So much variation from incidents account for the apparent irregularities of lunar interference at a glance, and need occasion no surprise. It is quite enough that we should trace especial action to its cause, though final results in detail were inconformable to that cause. The instance in hand becomes in so much a special case, and its merits must be treated accordingly.