believe it to be very great. There are soundings all around its shores from 10 to 20 miles out from Judda, in lat. 21° 30', to the approach of the volcanic region in lat. 17, and frequent cross soundings have been obtained from this southward to the strait. From 21° to 27° 30′, or for nearly 400 miles in length, there is a space from 50 to 70 miles in breadth, or an area of about 20,000 miles, that seems never to have been sounded; and this part has never been examined since the original survey was made 20 years ago. Being free from islands, reefs, and shoals, it occasioned no alarm to the navigators, and the surveyors had no time to devote to mere questions of physical geography. The greatest depth that seems ever to have been tried is 400 fathoms, lat. 25° 20', at which no bottom could be found; and there appears to be a gulf from 5 to 10 miles wide down the centre of the sea, varying from 150 to 250 fathoms, with abrupt and precipitous sides. The average depth of the central region of the sea to an extent of about 40 miles or so may probably be about 100 fathoms; the average depth of the whole sea probably falls short of 40. A reef or shallow runs across from Mocha, lat. 13° 30', to the African shore; it has been very carefully sounded all along; it affords an average depth of from 25 to 30 fathoms; its greatest depth being 40, near mid-channel. From this the sea deepens again to 125 fathoms as it approaches the strait. The great strait, as already mentioned. is 16 miles across; its average depth is about 80 fathoms, its greatest 125; and for a breadth of nearly 6 miles in mid-channel the depth exceeds 100 fathoms. The narrow channel being that which vessels from Aden almost always prefer in ascending the Red Sea, varies from 12 to 17 fathoms in depth, but there is 30 feet of water up to both shores with a fine sandy bottom, so that navigators feel no apprehension in traversing it at any hour. The Gulf of Aden, which continues the communication from the Straits to the Arabian Sea, is a funnel-shaped estuary above 900 miles in length and nearly 200 across from the N.W. point of Africa to the Arabian shore. Its general characteristics are similar to those of the lower part of the Red Sea-it is remarkable for the violence of its currents, which will be noticed afterwards, and for the depth of its central channel and shallowness of its shores.

The Tides at Suez are about 5 feet at neap and 7 at spring. The rise and fall at Ras-Mahommed is about 5 feet-high water at 6 o'clock. The direction of the wind makes a difference of about 4 feet in the depth of the water near Suez: the banks which are left dry by the N. wind are well covered with a breeze

The depths are taken from the chart, but the greater part of the soundings are marked as having "no bottom," so the actual depths are certainly beyond this,how much we know not.

from the S. We know little of the tides over the rest of the sea. At Aden, 80 miles without the strait, where continuous observations have been taken by gauge for three years, the tides rise 4 feet at neaps, and nearly 8 at springs; high-water occurring at 1:30; the sweep of the tides, as well as the hour of high-water, being remarkably irregular. The Red Sea probably derives its name from large portions of it, as well as of the Arabian Sea, being covered with patches, from a few yards to some miles square, of a blood-red colour, derived from a species of animalculæ particularly abundant in the spring months, and which dye the upper waters of the most intensely blood-red hue that can be conceived. There is nothing else about the sea that is red, and a considerable expanse of this, encountered by an early navigator who had not met with any similar phenomenon elsewhere, would seem warrant enough for its name.*

Islands.-Though islands are numerous along both shores of the Red Sea, they are for the most part of inconsiderable size,

Since the preceding remarks were in type I have fallen in with a paper by Ehrenberg on the bloody appearance of water, a translation of which appeared in 1831 in the tenth volume of Jamieson's Edinburgh Philosophical Journal. After enumerating instances quoted by the ancients of red snow, red rain, and rivers and seas covered with blood, he quotes a list of our experiences on these subjects in modern times. I take the following entire; he comes to the same conclusion as that which I have arrived at as to the origin of the name of the Red Sea:

"In 1823 I was for a number of months at Tor, on the Red Sea, in the vicinity of Mount Sinai. On the 10th December I there observed the striking phenomenon of the whole bay which forms the harbour of Tor of a bloody colour. The main sea beyond the coral reef that encloses the harbour was, as usual, colourless. The short waves of the calm sea, during sunshine, carried to the shore a bloody coloured slimy mass, which it deposited on the sands, so that the whole bay, fully half a league in length, at the ebb of the tide exhibited a blood red border of more than a foot broad. I took up some of the water itself with glasses and carried it to my tent at hand on the sea shore. It was immediately discovered that the colouring was caused by small flakes, scarcely distinguishable, often greenish, sometimes of a lively green, but for the most part of a dark red colour, although the water itself was not stained by them. This very interesting appearance attracted my attention as explanatory of the name of the Red Sea, a name hitherto so difficult of explanation. I, for many days and with perfect leisure, accurately examined the appearances and made microscopical observations on the colouring mass. The flakes consisted of small spiral or longish irregular bunches of oscillatoriæ threads, which were enclosed in a gelatinous sheath, and the flakes neither resembled one another nor the threads in each flake. In the glasses placed beside me I observed that the flakes during the heat of the day and in sunshine floated together on the surface of the water. During the night and when the glasses were shaken they descended to the bottom. After some time they returned to the surface. The observation made by Dr. Englehardt on Lake Murten was very similar to this appearance, and the delineation of the single threads by De Candolle exhibits a very close relation to it. De Candolle informs me he has preserved no dried specimen of that substance, for which reason no comparison can be made. The gelatinous covering and the union of many threads into very small spiral groups give to the substance of the Red Sea a peculiar character, which entitles it to form a particular genus of alga. The appearance of the Red Sea was not permanent, but periodical. I observed it several times: on the 25th and 30th December, 1843, and on the 5th January, 1844."

and they have been included in the measurement of the area: their structure will come to be spoken of along with that of the rocks on the opposite shores.

Temperature. The surface temperature of the Red Sea, agitated by the paddles of the steamers, varies from 60° to 85°. By a series of hourly observations made on it in April, 1840, when it ranged from 80 to 85°, it was in general from two to three degrees hotter than the air from midnight to dawn, and about as much colder from noon to sunset. Captain Newbold's observations for May, 1844, give from 82° to 84° as the midnight and noon temperatures, those of the air at the same hours being from 85° to 90°. The matter is one that has been but little attended to, though it is probable that the Red Sea scarcely differs in this from the outer ocean.

Appearance and Saltness of its Waters.-As the Red Sea is entirely surrounded by a hard, sandy, or rocky shore, without a rivulet, and scarcely a drop of rain falling into it from year to year, its waters are remarkable for their transparency and purity, even over a long expanse of shallows. Where the sea is deep and distant from the land, its colour is of the most intense blue, changing from greenish-blue to bluish-green, green, and light green, as the coral reefs approach the surface-the corals themselves being mostly white. It was long supposed to be considerably salter than the general ocean, a supposition now proved to be unsound. In 1837 Dr. Malcolmson found the water off Cossir of specific gravity 1·035, indicating a degree of saltness greater than that at Suez, but not so great as that of many parts of the Atlantic. The water at Mocha and Camran hardly at all differs from that of the outer sea. In 1848 Mr. Morris, engineer, obtained for me specimens of the water from seven different stations, nearly equidistant from each other all the way down: they were examined by Dr. Giraud, Professor of Chemistry at Bombay, and the following were the results :

-:

Dr. Giraud gives the following note of the saltness of the sea from a variety of other localities. From this it will be seen that the Mediterranean at Marseilles is of the same saltness as the Red Sea at Suez, while the Atlantic in the latitude of the Canaries is To more salt.

These experiments were made on water taken from the surface of the sea. We are ignorant of the character of the water in its depths, but have no reason to suppose it to differ materially from that at the surface.

Climate and Winds.-From the general conformation of its shores, the winds in the Red Sea for the most part blow in the direction of its axis, being for eight months in the year from the N.W., for the remainder from the S.E. The characteristics of the climate of the upper and lower portions of the sea differ, as may be expected, materially from each other, that of the middle portion partaking occasionally of both. The N.E. monsoon, which commences in October and continues till May or June, blows with considerable freshness in February, but is, as summer sets in, occasionally interrupted almost altogether. On entering the Red Sea it is deflected, and pursues a path almost at right angles to that which it had previously pursued, becoming a south-easterly wind as it rushes up the axis of the sea. Confined in a comparatively narrow compass, it blows with considerable violence, and is stronger towards the Arabian than the Abyssinian shore in the lower part of the sea. It is freshest in the end of October and beginning of February, and is sometimes felt as far up as Suez, so that generally by the time that it gets as high as Judda, lat. 21° 30', it becomes for the most part light and variable. It slackens as it passes the Harnish and Zugar islands under the 14th parallel, where the sea begins to extend in breadth. Further to the northward it softens still more, till it is lost in the languid winds on the coral reefs of the Arabian coast, or turning to the westward, wanders away out towards the islands of the African shore, until, changing its course, it returns again into itself. In October and January the weather in the lower part of the sea is thick and hazy, obscuring objects until they are close at hand, and squalls and rain are frequent and heavy. Captain Ellowan states, that in December land and sea-breezes were prevalent on the Arabian shore, half way up the Red Sea, with occasional southerly winds; in January it was frequently squally, with thunder, lightning, and some rain in the southward, occasional squalls being experienced in February. On the African coast, in lat. 15°, the prevailing winds in March are westerly, drawing off from the land towards night, from the sea during the day. In April regular land and sea-breezes pre

vailed, the winds generally from the N., though twice or thrice from the S., and the weather often hazy. In May the wind mostly comes from the land, the sea-breezes becoming light, sand squalls being experienced towards the beginning of June.

When the south-easterly monsoon begins to blow in the northwesterly part of the Indian Ocean, north-westerly winds prevail in the lower half of the Red Sea, where they blow with considerable violence in June and July, becoming light and variable in August and September. As the time of their extinction approaches, there are sometimes calms of several days' duration experienced, when the sea-breezes become excessive. On the African shore, sea and land breezes are experienced towards the strait, with northerly winds nearly all the year round. The fine season prevails from August to October; showers, such as they are, are chiefly experienced from November to March. The winds from Suez to Judda are mostly northerly throughout the year, and occasionally blow with considerable violence. From December to April southerly winds are occasionally experienced in the Gulf of Suez, at times freshening into a gale, and blow for several days. Captain Carless tells us, that it is almost always stormy in the Gulf of Akabá, the squalls being dangerous and violent where the two gulfs unite. Captain Cruttenden states, that when he visited Senna in July, 1836, no rain had fallen, either there or at Mocha, for four years, but that during his stay heavy rains fell for nearly a month. These remarks are all taken from the writings of the officers on the survey, some of which still remain unpublished, and are mostly from the sailing directions of Captain Moresby. We have no regular meteorological observations from any part of the Red Sea higher up than Aden, where the evaporation amounts to about 7 feet annually. Off the peninsula of Sinai, according to the experiments of Captain Carless, it amounts to between 8 and 9 feet; and when the dryness of the desert winds is taken into account, the evaporation over its whole surface will probably be found to fall little short of 8 feet annually; and certainly not more than an inch of rain or rain-water is added in the course of the year; the showers, heavy as they are, which occasionally fall on its shores being drunk up by the thirsty sands which cover them all around.

Currents. From the general character of the sea as just described, a very singular series of occurrences may be expected to make their appearance near the strait, to compensate an evaporation of nearly a quarter of an inch daily, or nearly 8 feet annually, over an area of 108,154 miles, or in all 165 cubic miles of water raised in vapour in excess of the little rain that falls. Were the geological theory true, that the water, concentrated at the surface, occasioned a deposit of salt at the bottom, the Red Sea must long