Royal Society. 67 



way from Tripoli and since my arrival here. My instruments are 

 almost all in good condition, although their cases have split from 

 the effects of heat and dryness, notwithstanding their double, and in 

 some instances triple, leatlier protection. I saw the great comet for 

 the first time on August 23, but others had seen it three or four 

 days sooner. Its nucleus was very bright, resembling a star of the 

 first magnitude, with a distinctly defined disc of the apparent dia- 

 meter of Jupiter. The tail made an angle of 86° or 87° with the 

 horizon, inclining to the north. It was a single tail with almost 

 precisely parallel sides. Its length was 10° on the 25th of August, 

 12° on the 26th, and 15° on the 27th and 29th of August. I have 

 seen here repeatedly the apparent fluctuation in the position of stars 

 Avhich is spoken of in the third volume of Cosmos, and have sent the 

 particulars of my observations to Baron von Humboldt. There is 

 no regular rainy season at Mourzuk, but slight showers occur 

 sometimes in the winter and spring, seldom in the autumn. A heavy 

 rain is considered a great calamity, as it destroys all the houses, 

 which are built of mud dried in the sun. It would likewise kill the 

 date trees, by dissolving the salt which is in large quantities in the 

 soil. About twelve years ago there perished above 10,000 date 

 trees in the neighbourhood of Mourzuk, on account of a rain which 

 continued for seven days. The prevaihng winds are south and east, 

 the strongest generally west or north-west. Twice or three times 

 I have seen whirlwinds pass through the town, a phenomenon which 

 was common in the deserts between Benioleed and Mourzuk. AU the 

 whirlwinds I observed turned in the direction from east by north 

 and west to south. In December and the first half of January the 

 thermometer falls at sunrise (at Moorzuk) as low as 42°, and in 

 places exposed to the wind water freezes during the night. At 

 Sokna I found no one who could remember having seen snow ; but 

 at Ghadamis snow was seen by Mr. F. Warrington on the 15th of 

 January 1831. At Tripoli we had heavy dews at night; and I 

 observed the same until we had passed a small chain of mountains 

 fifteen miles north of Sokna ; from thence we had no dew, and it was 

 even often impossible to get the dew-point with Daniell's hygro- 

 meter. In the desert the thermometer generally rose till 4 p.m., 

 from the sand (which was sometimes heated to 140" at 1 p.m.) giving 

 out its heat. Earthquakes are unknown in Fezzan ; slight shocks 

 are sometimes felt at Benioleed and Sokna, as was the case the end 

 of last May. Sliooting stars were observed in great quantities 

 (about forty an liour) on the 7th, 8th, and 31st of July; very few 

 on the evenings of the 9th, 10th, and 11th of August, averaging 

 fifteen an iiour, mostly coming from Cassiopea and Ursa Minor. On 

 the 10th, at 8 a.m., I saw in ten minutes three shooting stars coming 

 from a Cassiopea;, and rising right ujjwards towards the zenitli. 

 About 4 A.M. on the 11th, J observed in a (juarter of an liour about 

 twenty very bright ones in Pegasus and Aries. Shooting stars were 

 numerous also on the 1st, 2n(l and 3rd of October." 



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