337 
of Dust and Ashes. 
colour with the hues of ashes erupted, at the same time, 
from known volcanoes. Thus we are told that, during the 
eruption of Vesuvius on the 16th of December, 1631, (of 
which mention has been before made), the ashes which fell 
at Lecce were not of the same quality with those which fell 
at Bari* : and persons who have met with ashes in situ on 
volcanoes know, that the colours vary not only in different 
eruptions, but during one and the same convulsion.+ 
* Discorso sopra V Origine di Fuochi del Monte Vesuvio di Gio 
Francesco Sarrata Spinola Galateo. 
+ 1 he following notes are selected from the journal of the late Mr. 
John Davidson, who was detained for some months, in 1835-6, at 
AY ad Nun, on the borders of the Sahara; they contain the only actual 
evidence of dust blown from the African desert. The latitude of 
Wad Nun is about 28° 30' N. It will be seen, that though the dust on 
the 3rd August came in the teeth of a strong contrary wind, yet there 
is nothing to show that the dust was in such volumes as to have been 
carried out to sea, in opposition to the usual ocean winds, leagues 
from land. 
“ Saturda y, J uly 30, 1836, tlier. 75°. The night has been cool, 
and very pleasant. Towards the middle of the day the heat returned 
with great power. A simurn is blowing in the desert j we are all 
covered with dust, and the houses are perfectly obscured. 
“ July 31, ther. 80°. In the afternoon we felt the simurn again, and 
the night was oppressive in the extreme. 
“ August 1, ther. 86°. The whole horizon buried in a ckud of 
dust. The mountains to the S. and S- E. were not visible. 
“ Aug. 2, ther. 80°. 
“ Aug. 3, ther. 75°. Much cooler. There is a strong breeze, but 
the dust still comes from the desert. For the last three nights we 
have been annoyed with the jackals, who have been driven in from 
the Sahara. About seven jackals have made their appearance. 
“ Aug. 4, ther. 76°. A high wind, with dust, which nearly 
blinded us. 
“Aug. 14, ther. 63°. A sand wind from the desert; the glare 
producing mirage. 
“ Aug. 17. The wind is high, but with the haze over the moun¬ 
tains, the forerunner of the heat. At 11 a.m. it blew a perfect hur¬ 
ricane. The simurn felt like the blast of a furnace. The therrno- 
VOL.I. NO. V. 
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