motion, reaches the shore with its desolating surge, long after the real shock has spent its violence on the land. The earth wave varies from an inch in height to two or three feet, and when it comes to shallow soundings "it carries with it to the land a long, flat, aqueous wave." On arriving at the beach, the water drops in arrear, from the superior velocity of the shock, so that at that moment the sea seems to recede before the great ocean wave arrives.

"Three other series of undulations are formed

subsidence marked out by the coral islands and reefs of the Pacific: and " there is not an active volcano within several hundred miles of an archipelago, or even a group of the Atolls or Lagoon Islands. The volcanic islands are, generally speaking, arranged in zones, one of the most active of which is the Banda group, including Timor, Sumbawa, Bali, Java, and Sumatra, forming a curved line 2,000 miles long." The little island of Gounong-api, belonging to the Banda group, contains a volcano of great activity; and such is the elevating pressure. of submarine fire on that part of the ocean, simultaneously with the preceding, by which the that a mass of black basalt rose up, of such sound of the explosion is conveyed through the magnitude, as to fill a bay sixty fathoms earth, the ocean, and the air, with different velocities. That through the earth travels at the rate of deep, and so quietly, "that the inhabi- from 7,000 to 10,000 feet in a second, in hard rock, tants were not aware of what was going on and somewhat less in looser materials, and arrives till it was nearly done." The second zone at the coast a short time before, or at the same of volcanic islands, containing many open moment with the shock, and produces the hollow vents, begins to the north of New Guinea, sounds that are the harbingers of ruin; then foland passes through New Britain, New Ire- lows a continuous succession of sounds, like the land, Solomon's Island, and the New He- rolling of distant thunder, formed, first, by the brides. The third, and greatest of all the sea, which travels at the rate of 4,700 feet in a wave that is propagated through the water of the volcanic zones, commences at the north ex- second, and, lastly, by that passing through the tremity of Celebes, including Gilolo," bris-air, which only takes place when the origin of the tled with volcanic cones," the Philippine earthquake is a submarine explosion, and travels isles, Formosa, Loo-Choo, and the Kurile with a velocity of 1,123 feet in a second. The isles of Kamtchatka, which contain several rolling sounds precede the arrival of the great wave active volcanoes of great height. Volcanic on the coasts, and are continued after the terrific catastrophe, when the eruption is extensive."eruptions in the Japan Archipelago occur P. 229. in six islands east of Jephoon; and in the Kurile islands the internal fire has shown itself in eighteen volcanoes. In the beginning of this century there appeared two new islands, one five miles round, and the other 3,000 feet high, in a part of the ocean so deep, that a line of 1,200 feet did not reach the bottom. "On the other side of the Pacific the whole chain of the Andes, and the adjacent islands of Juan Fernandez and the Galapagos, form a vast volcanic area, which is actually now rising." In the table-land of Western Asia, where the internal fire had once been intensely active, we have now only the spent volcano of Demavend, from whose snowy cone smoke occasionally issues. In the table land of Eastern Asia there is only one volcano in the chain of Thian-Chan.

The earthquake which destroyed Lisbon had its centre of action immediately below the city, and shook "an arc of 700,000 square miles, equal to a twelfth part of the circumference of the globe.”

Mrs. Somerville now proceeds, in her fifteenth chapter, to treat of the OCEAN-its size, color, pressure, and saltness; its tides, waves, and currents; its temperature; its Arctic and Antarctic ice, and its inland seas. The bed of the ocean is diversified, like the land, with mountains and plains, with tablelands and valleys-here barren, there covered with sea-plants, but everywhere teeming with life. The detritus of the land is continually filling up its bed, but this is counteracted by the elevation of the land, which keeps its shores invariable. In those parts of the earth where the in- Great Pacific Ocean has a larger area than ternal fire has not found an easy exit, earth- all the dry land on the globe. It covers quakes of various degrees of intensity fre- 50,000,000 of square miles, and 70,000,000, quently occur. When the boiling lava including the Indian Ocean. From Peru within forces itself up beneath the ocean, to Africa it is 16,000 miles wide. It is it gives birth to two waves-one along the generally unfathomable between the tropics, bed of the ocean, which is the real shock of where its depth is so great, that a line five the earthquake, and the other on the aque-miles long has in many places not reached ous surface, which, travelling with a slower the bottom. The Atlantic Ocean, appa

The

rently stretching from Pole to Pole, is 5,000 | Turury channel at Cayenne the sea rises 40 miles wide, and covers 25,000,000 square feet in five minutes, and as suddenly ebbs. miles. The following are its depths in different places:

27,600*

The highest waves which occur at the Cape of Good Hope do not exceed 40 feet from their lowest to their highest point. Under the heaviest gales the sea is probably tranquil at the depth of 200 or 300 feet.

In 15° 3' 5" Lat., and W. Long. 23° 14', The tranquillity of the ocean is disturbed as high as the Himalaya. by currents varying in their extent and veThe German Ocean, now rapidly filling locity, owing to causes both permanent and up by the detritus from the land, has in a variable. The great currents which flow great part of its bed a depth of only 93 from the two poles to the equator, are defeet! and even near the precipitous coast of flected by the diurnal motion of the earth, Norway the depth is only 5,460 feet. At acquiring a rotatory motion as they adthe depth of a mile and a quarter the pres- vance, till they combine into one great cursure of the sea is equal to 2,809 lbs. on rent flowing from east to west with the veevery inch of surface. In the Arctic Ocean locity of nine or ten miles a-day. The shells are seen at the depth of 1,180 feet, Gulf stream, and other currents, which we and among the West Indian Islands at 180 have elsewhere described, originate from feet, so that the light which fell upon these this great "oceanic river." shells would have been visible to an eye at least 960 feet deep in the one case, and 360 feet in the other. The color of all water when pure is a fine bright blue, becoming green when mixed with certain vegetable matters, and brownish yellow when derived from mosses. The saltness of the sea is greatest at the parallel of 22° N. Lat. and 17 S. Lat., diminishing towards the Equator and the Poles, where it is least, owing to the melting of the ice. At the Straits of Gibraltar the water is four times as salt at a depth of 670 fathoms as it is at the surface.

As the mean temperature of the earth at the poles is about 10° of Fahrenheit, and about 2° or 3° below zero at the two poles of maximum cold, 12° distant from the poles of revolution, and situated in the meridians of Canada and Siberia, the Arctic and Antarctic Oceans are completely frozen during eight months of the year, a continuous body of ice, extending round the poles of maximum cold, and occupying a sort of elliptical area above 4000 miles in its mean diameter. The icebergs which are detached in pieces from the glaciers, that lie on the margin of this gelid region, are sometimes drifted southward 200 miles from their origin. The largest and the farthest travelled icebergs come from the South Pole. Capt. D'Urville observed one thirteen miles long, with perpendicular sides 100 feet high.The icebergs of the Arctic Zone have been already described; and, in our review of Sir James Ross's voyage, the reader will find interesting details respecting the ice-masses of the Antarctic Ocean, and the dangers of navigating an icy sea.

The central area of the Pacific and the Atlantic is occupied with the great oceanic tide-wave, which is raised by the joint ac tion of the sun and moon. From this continually oscillating wave, partial waves diverge in all directions, finding their way into seas and estuaries, with various velocities, depending on the form of the coast and the depth of the channel, and the nature of its bed. In some parts of the coast of Britain the tides rise 50 or 60 feet. In the Bristol Channel and the Gulf of St. After describing the inland seas* which Malo they rise 47 feet, according to Cap-diverge from the two great oceans, and tain Beechey, and at the Bay of Fundy 60 which, in the case of the Atlantic, have a feet, while at St. Helena they never exceed coast of 48,000 miles, and of the Pacific three feet, and are scarcely visible among only 44,000, Mrs. Somerville proceeds in many of the tropical islands in the Pacific. her sixteenth chapter to the subject of At Courtown, according to Captain Beech-springs, hot and cold, and to the origin and ey, there is little or no rise of the water, and at Swanage the Spring-tides are scarce ly five feet.

The tide at the equator follows the moon at the rate of 1,000 miles an hour. In the

*The line did not reach the bottom.

cause of floods in rivers, devoting the other two chapters of the first volume, and the two first chapters of the second, to the de

scription of the river systems and lakes of the great continents of the earth.

on the River or Hydraulic systems, and on the Lakes in the Old and New World. It is impossible, indeed, to peruse these chapters with the interest which they possess, unless we have before us excellent charts of the river systems themselves, free of all the other details which are given in ordinMaps of this kind, of great beauty and accuracy, have been published by Messrs. Johnston and Berghaus; and we would recommend to our readers to study this part of Mrs. Somerville's work with these beautiful hydrological plates in their hands.*

Although hot and boiling springs are most common in volcanic regions, yet they are often found at the distance of many hundred miles from volcanic districts. In the Austrian dominions there are no less than 1,500 medicinal springs, contain-ary maps. ing sulphuric and carbonic acids, iron, magnesia, sulphur, iodine, and other ingredients. The boiling springs of Iceland, Italy, and the Azores, deposit silex; and all over the world there are springs that deposit carbonate and sulphate of lime in enormous quantities. The brine springs of Cheshire have flowed unchanged for 1000 years."Springs of naphtha and petroleum are abundant round the Caspian sea," the petroleum forming even lakes in that singular region.

In treating of River systems, hydrologists divide the subject into eight different parts- the Basins-the Watershed and Portage-the Bifurcations-the Size and Length of Rivers-the River Courses- the Deltas--the Velocity of Rivers, and their In the physical geography of rivers many Development. The basin of a river is the interesting phenomena are presented to the whole sources, brooks, and rivulets, whose student. While it is the general character waters contribute to its formation--or the of a river to advance with an increasing surface of the country which it drains. quantity of water to the sea, there are cases The watershed is the place where waters where rivers and streams are absorbed by begin to descend in opposite directions. the soil, and are actually lost before they When the watershed is flat, so that barges reach the ocean. At the Perte du Rhone can be easily conveyed over it from one the river disappears and re-appears, and river to another, the places where this can there are streams in Derbyshire which are lost for a time and again rise to view. When the Arve which runs into the Rhone below Geneva is swollen by a freshet, it sometimes drives back the Rhone into the Lake of Geneva, and on one occasion the retrograde current actually made the millwheels revolve in the opposite direction.

be done are called portages. When opposite river basins are separated by a country so depressed on its surface as to permit the water of one river, when diverted from its channel, to join another river with which it has no connexion, the phenomenon is called the bifurcation of a river. There are many such bifurcations in America, and "Instances have occurred of rivers suddenly in the deltas of rivers generally; but the stopping in their course for some hours, and leav-most remarkable is that in which the Casiing their channels dry. On the 26th of Novem- quiare (which our countryman, Sir R. ber, 1838, the water failed so completely in the Schomberg,† lately found to be 120 miles Clyde, Nith, and Teviot, that the mills were

stopped eight hours in the lower part of their long in direct distance, and 176 in its streams. The cause was the coincidence of a windings), flowing through the plains of gale of wind and a strong frost, which congealed Esmeralda, unites the Orinoco with the the water near their sources. Exactly the contrary happens in the Siberian rivers, which flow from south to north over so many hundreds of miles; the upper parts are thawed, while the lower are still frozen, and the water, not finding an outlet, inundates the country."-P. 270.

The tides of the ocean often flow up rivers to a great distance from their mouths, and frequently to a height far above the level of the sea. In the Amazons, the tide is perceptible 576 miles from its mouth, and in the Orinoco it ascends 255 miles.

It would require much greater space than our limits allow, to give even the briefest abstract of Mrs. Somerville's four chapters

Maranon. It is 300 feet wide where it leaves the Orinoco, and 1650 where it joins the Guainia, a tributary of the Maranon. The size and length of rivers, including their windings, is an indication of their importance both in navigation and commerce. in the progress of a river, it is divided into the upper, the middle, and the lower course. The upper course is generally through rap

*These charts, two in number, form Plates V. and VI. of the department of Hydrology in the

Physical Atlas, and represent the Oceanic Rivers;
the Continental Rivers, and the River Basins.
p. 248.

Journal of the Geographical Society, vol. x,

ids, the middle course through plains, and and the volume of water they contain. the lower where it tends to divide and ram- The development of a river is its length ify forms Deltas (so called from their re- from its source to its mouth, including all semblance to the Greek letter Delta A), its windings and turnings. Following which are divided into fluviatile, lacustrine, Johnston and Berghaus in their definitions, and maritime—fluviatile, when the river falls we shall now present, on their authority, into another-lacustrine, when it falls into the following abridged view of the differa lake and maritime, when it falls into ent River systems in the Old and New the sea. The velocities of rivers indicate Worlds :

the form and inclination of their channels,

If we reckon the whole running waters of Europe to be unity, or 1.00, the quantities discharged into the different seas will be

Hence the Black Sea swallows up the third part of all the running waters in Europe!

The quantity of water discharged by each of the European rivers will be as follows, assuming all the rivers to give 1.00 parts.

With the following table, showing the characters of the great American lakes, we must conclude our observations on the Hydrology of the earth :*

From the physical geography of the waters ing details of which they are susceptible. of the globe, Mrs. Somerville proceeds in Mrs Somerville will, no doubt, supply the the twentieth chapter to the consideration of defects of this chapter in a second edition, the Air, or the Atmosphere-its density-its and dwell at greater length upon these and currents-its temperature-its moisture- other topics which are little more than its electricity-its diamagnetism, and its mentioned. There is, in our opinion, no constituents. These important subjects department of Physical Geography so inare treated in the narrow space of ten pages, and of course without any of those interest* The reader will find more ample details in the letter-press descriptions of Berghaus and Johnston's Hydrological Maps, Plates V. and VI.

M. Doyer has very recently shen that the composition of the atmosphere is constantly changing, the quantity of oxygen varying from 20.5 to 21.3. Comptes Rendus, &c., 24 Fev., 1848, p. 194, and 21 Fev., p. 234, Nole.

teresting as that of the atmosphere, and none certainly with which we are so intimately connected, and in which we are so deeply interested. Mrs. Somerville does not even mention the Isothermal lines of Humboldt and his fellow-laborers; nor the optical phenomena of the atmosphere, such as its polarization, its colors, its phenomena of unequal refraction; nor its optical