374 



mode of formation would render it probable that it is the true ana- 

 logue of carhanilic acid. The determination of this question is of 

 some interest, inasmuch as should it prove to correspond to anthra- 

 nilic acid, a road might through it be opened for the introduction of 

 a series of new substances at present entirely wanting, namely, the 

 proper homologues of salicylic acid and its derivatives. The author 

 proposes to return to this subject, and he gives, in conclusion, a syn- 

 optical view of those corresponding members of the henzoyl and toluyl 

 groups which in the present and former paper he has established. 



December 15, 1853. 

 THOMAS BELL, Esq., V.P. in the Chair. 



The following communications were read : — 



1. Extract of a Letter from Dr. Edward Vogel to Colonel Sabine, 

 dated Mourzuk, Oct. 14, 1853. 



" You will receive through the Foreign Office a packet of Astro- 

 nomical, Meteorological, and Magnetical Observations, made on the 

 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, leather 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 

 which 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 prevailing 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. All 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 



