FOREIGN CORRESPONDENCE. 
87 
The temperature of the earth, at a depth of six feet, should then, if 
the general law of increase of heat be observed, range only one-tenth 
higher than that observed at the surface of the soil, and not two-tenths, 
as stated above. It is a curious fact that points situated on the same 
vertical line, at an inconsiderable depth within the interior of the 
earth, experience at very diflerent times the maximum and minimum 
of atmospheric temperature. Thus, Quetelet affirms, in the Bulletin 
de VAcademie de Brnxelhs, for 1836, that daily variations of tem- 
perature are not perceptible at depths of about four feet below the 
surface ; and at Brussels, the highest temperature was not indicated 
until the \Qth December, on a thermometer which had been sunk to a 
depth of more than twenty-five feet, whilst the loivest temperatm-e 
was observed on the \5th of June. Professor Forbes, from experi- 
ments made at a depth of twenty-four feet in the basaltic trap of 
Calton Hill, near Edinburgh, obtained similar results : the maximum 
of heat was not observed until the %th of January. According to 
Arago, very small differences of temperature are perceptible at about 
thirty feet below the surface. The stratum of invariable temperature 
is, in the well-known Caves de I'Observatoire, at Paris, at a depth of 
eighty-six feet English. 
A letter from Naples informs us that " Vesuvius is cracking and 
splitting ; the foot of the cone being pierced through and through by 
fumarolle, or little craters, which emit a considerable quantity of 
lava. ... If this sort of work continue, the great cone, formed by 
the accumulation of substances thrown out by the volcano, will pro- 
bably fall in one of these days ; and the result will be a terrible catas- 
trophe, not for Naples, which lies comfortably at a certain distance, but 
for Resina and Portici, which lie at the foot of this formidable moun- 
tain." It would certainly be a strange thing to see Vesuvius over- 
whelm these towns, built upon the very lava which smothered up 
Herculaneum. Professor Daubeny, of Oxford, the author of a well- 
known work on volcanos, is at pi'esent at Vesuvius. 
A terrible earthquake took place in Turkey, on the 28th November, 
principally at Touzla, in the district of Zvornie. Many houses fell, 
and the inhabitants, in spite of the cold weather, were obliged to quit 
then- dwellings and encamp in the open fields. Another still more 
disastrous shock has nearly overthrown the town of Ergheni, in 
Albania. A number of houses and shops were completely destroyed, 
and many people killed. 
We have received some more news of the submarine volcano men- 
tioned in our last article. The French consul at Livoruo (Leghorn) 
has communicated the fact to the Paris Academy of Sciences. Accord- 
ing to his account, flames and smoke were seen to issue from rocks 
which have taken the place of the ancient pier. All around the tem- 
perature of the sea is above boiling-point (100° Centigrade). It 
is evidently a volcanic phenomenon similar to that which caused the 
upheaval of the remarkable island called Julia, or Sabrina, not very 
far from the same place. 
