Early the next morning we fet fail with a pleasant breeze, and before night, entering the ftraits of Gibraltar, had the fatiffaction to view the proud rock, at the fight of which every British heart should triumph in the recollection, not so much of the courage of its brave defender, as of his generous compaffion for his befiegers in the hour of their diftrefs. As we had the advantage of the current, we flackened fail, that we might be certain of not paffing Malaga before the morning. But, by the time that we had entered the bay, and began to fee the city at a diftance, the wind died away, and for two hours we found ourfelves becalmed. However, as the day advanced, the fea breeze got up, and foon carried us to the place of our destination.

We have here two phenomena, univerfally noticed, but never fufficiently accounted for: the conftant influx into the Mediterranean, and the fea breeze. Both have occupied the attention of philofophers; and their folutions, however fatiffactory to themselves, have not, as I conceive, removed the difficulties involved in thefe fubjects.

3

Doctor

Doctor Halley, in his experiments to afcertain the quantity evaporated from the Mediterranean Sea, placing a veffel of faltwater over burning coals, brought it to the temperament of the air in our hottest fummer; and at the end of two hours, having found the evaporation and the proportion of the furfaces to each other, from these he formed his calculation. He then attempted to difcover the quantity of water annually poured into the Mediterranean by all its rivers, making his calculation by the produce of the Thames; and finding this unequal to the evaporation, he concluded, that he had affigned a fufficient cause for the conftant influx. How inaccurate the premises! how hafty the conclufion! Not to mention his comparing the discharge from rapid ftreams, borne with impetuofity into the Mediterranean, and retaining their freshness at the diftance of many leagues from shore, with the more humble produce of the Thames, creeping almoft imperceptibly along, and loft as foon as it has reached the fea; not to mention the impropriety of this comparison, it may be fufficient to remark, that the whole quantity of water

contained in his veffel was brought to the temperature of the air in our hottest fummer. No wonder then, that he should make the evaporation from the furface of the Mediterranean amount to two hundred and eighty millions of tons per day. But that furface is feldom, and but for very tranfient moments, of the fame degree of heat with the incumbent atmosphere, because every breeze muft make a confiderable variation in its temperature, by commixing the waters from a confiderable depth with those that are fuperficial. In a most interesting voyage among the Alps, by M. de Sauffure, we find fome experiments conducted by himself on the lake of Geneva, by which it appears, that on the 6th of Auguft, 1774, the thermometer of Reaumur at the depth of three hundred and twelve feet, stood at eight degrees and an half, when near the furface it was fifteen degrees, and, in the air, twenty degrees.

Here we find five degrees of difference between the heat of the atmosphere and the surface of the water in calm weather; but how much greater would have been the variation, had the lake been ruffled by a ftorm,

ftorm, more especially had the waters been troubled to the depth of fix hundred and twenty feet, where, as it feems, the thermometer funk down to four degrees threetwentieths.

Hence it appears, that the calculations of Dr, Halley are ill grounded. That his conclufion is erroneous, will be evident, if we reflect, that fuppofing the evaporation to exceed the annual fupply from rivers, the Mediterranean Sea would be constantly growing more briny than the ocean, till, in procefs of time, it would become one folid mafs of falt.

This being the cafe, fome other cause must be affigned for this interesting phenomenon. Suppofing the fact to be well established, that the influx at the ftraits of Gibraltar does really exift, without any correfponding efflux by the fame channel, there must be fome invifible communication between the Mediterranean and the ocean; and this, confidering the ftrong convulfion our globe has at fome period fuffered, is by no means improbable.

The other phenomenon, not fufficiently accounted for, is the fea breeze. It has B 3 been

been supposed to arife merely from the accumulation of heat on the earth by day; as the land breeze is conceived to originate from the diminution of that heat by night. But we might enquire, whether the furface of the earth, by night, becomes colder than the furface of the water? if not, fhould not the fea breeze continue all the night?' but this would be contrary to fact. That accurate obferver, Dampier, has given a good description of these alternate changes in the direction of the wind on the coaft, and at a few leagues diftance from the land. He fays, "The fea breeze begins about nine " in the morning, fo gently, as if it were "afraid to approach the shore; and then,

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as if unwilling to offend, it makes a halt, and feems ready to retire. It increafes "till noon, and dies away about five in the " evening."

*

From the refult of fome experiments confirmed by my own obfervation, I am induced to believe that the fea breeze originates in the afcent of vapour from the sea, and the land breeze from the condenfation of that vapour, .1

That one cubic foot of water may be

con