Page 508 - Travels in Arabia (Vol 2)_Neat

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APPENDIX. 469

the ingress and egress direction of the current, and
the ebb and flow which I had observed at its ex­
tremity. It had appeared to me singular, that the
absence of any apparent regular, not to say constant,
current at the entrance, should hitherto have escaped
notice; for in this respect it presents a singular excep­
tion to the indraught which is usually experienced at
the entrance of inland seas; especially with those
having narrow mouths. Dr. Halley was of opinion
that the expense of water by evaporation was alone
sufficient to account for the continued drain from the
Atlantic to the Mediterranean. The mean surface of
the water in the Red Sea is not certainly equal to that
of the Mediterranean ; but to counterbalance this, the
agents which produce this effect are more powerful in
the latter than in the former. The theory advanced,
is simply, that as the atmosphere over the land be­
comes considerably warmer than the sea during the
day, a current of cooler air moves towards the shore,
and then deposits its humidity either in dews or rains;
and that a constant supply is necessary to fill up the
deficiency thus drawn off. It will readily be believed
that the burning deserts on either side of the Red Sea
are well calculated to produce such effects. Rain is
not indeed often met with, but the dews are so sin­
gularly copious, that in the vicinity of the land, I have
known them to leave on our masts, sails, and rigging,
all the effects of a smart shower.
I have elsewhere had occasion to remark that this
irregularity appeared to be in a great measure in­
fluenced by the direction of the wind, which blows with
much violence, though with great regularity, from dif-