18 REPORT—1848. 
‘same wind continues all the year round from Suez to the Straits of Jubal, and with 
particular violence down the Gulf of Akabar. During the remainder of the year 
the winds in the middle part of the sea, from Jebbel-Teir, 15°30 to 19° or 20° N., 
are light and variable. In the south part, again, from Jebbel-Teir to the Straits, 
the S.E wind is constant from October till May, increasing in violence as you ap- 
proach the Straits. This we experienced ourselves, for we carried N. and N.E. 
winds from Suez to lat. 20, variables from lat. 20 to Jebbel-Teir, and southerly from 
Jebbel-Teir to the Straits. I do not know how far the accompanying phenomena 
may account for the great saltness and well-known depression (below the level of 
the Mediterranean and of the Straits amounting, if I remember aright, to 35 odd 
feet) of the upper part of the sea; my observations give the following results :— 
Vapour in | Calculated 
M i Wet-bulb ¢ 
rig Boni a, Dew-point.| oubie feet. evaporation 
Suez to lat. 20°. oe cas... 761 78:0 68°3 64:1 6°841 1-56 
Lat. 20°, Jebbel Teir ...... 81-6 80-4 74:5 71-4 8-478 1:38 
Jebbel Teir to Straits ...... 80:3 76-0 70-2 65-0 4311 261 
“The perennial north wind of the upper portion may of itself reduce the level ; it 
is, further, a drier wind, and effects more evaporation from the surface than do the 
winds of the middle portion, at which it arrives loaded with vapour and increased 
in elasticity. Whatever evaporation takes place at the south portion again, during 
the dry south wind, may be compensated by an indraught from the Indian Ocean. 
The central portion again, during the same season, receives the loaded currents from 
either quarter, which its high temperature enables it to retain, its elasticity being 
also very high. ; 
“‘ Few other phenomena of any importance occurred to me during the voyage, 
except a curious variety I suppose of the crepuscular arch, which I witnessed on two 
nights after leaving Madrasroads. The first I saw on January 9th at 63, while 
still in sight of land ; it lasted hardly a minute after I first caught it, and appeared 
like a broad lunar rainbow over the sun’s position, and about 70° alt. On the 
following evening I looked out for it; we were some 150 miles on our course to 
Calcutta. At three-quarters of an hour after sunset a pale milk-white arch, with 
the faintest tinge of purpie, appeared at 60° alt. It was about 8° broad, the north 
end rested on a very faint cirrhus, alt. 30°; the southern descended lower, but did 
not reach the horizon; its limits were not clearly defined ; it rose rapidly, and dis - 
appeared in about three or five minutes on reaching the zenith. The days had in 
both cases been very fine and clear, the sky at the time deep blue gray, with a 
peach-blossom tinge (for twilight) resting on a yellow horizon. This peach colour 
is a very common tropical sunset, and for delicacy of tint unequalled. At Aden, 
where contrasted with the stern pitchy dark crags of that peninsula and deep blue 
of the ocean, it produced the finest sunset effect I ever witnessed.” 
After describing some particulars of his instruments and methods of meteorolo- 
gical research, the author adds,—I have twice had bores made of 3 and 4 feet at © 
places 14’ apart, and in both cases had a constant temperature of 72° for fifteen hours 
of afternoon and night ; but this alluvium is often too hard to bore with common tools ; 
it always takes six hours and six men to work the jumper. I guard the bulb with 
pith and sink it in a brass tube. The dryness of the upper plains we traversed is 
wonderful during these N.W. winds. I have been very careful with the wet-bulb 
observations. Solar radiation is all but impracticable; I persevere in the black bulb 
and wedge of glass photometer, made as you recommended by Darker. 
“Last night I saw the best-developed aurora I ever witnessed, taking brightness, 
extent of surface covered, and length and continuity of beams into account : never in 
Scotland, where I have seen many, or the South Pole, where also they were frequent, 
have I seen one so altogether good as this. The moon spoiled it-sadly, though its 
beams were brilliantly defined within 8° of her orb on each side. I send you the 
observations I took of it with a good quadrant and compass, from my-first seeing 
it till it had nearly disappeared at midnight. I have also sent an account to be 
published in Calcutta, and hope it has attracted observation elsewhere. There is 
no change in the weather since, but much cirrhus since noon to-day, which is un- 
