a7 
_of the Black Sea and Caspian Sea. 369 
Mediterranean Sea is lower by eight millimetres at low water 
and nine millimetres at the high water of the Red Sea. One 
part of the basin of the bitter lakes is remarkable for its being 
eight metres lower than the level of the Mediterranean, which 
consequently places it 16 metres lower than the Red Sea: other 
points of the soil and even of the inhabited places are lowerthan 
the levels of both seas, The water of the Red Sea, for instance, 
might cover the whole of the surface of the Delta, and the ter- 
rors of submersion were, as has been seen, natural enough at 
distant periods, when this part of Egypt was less elevated than 
it is at present. 
For want of observations exactly correspondent for estimating 
the difference of elevations of two very distant stations, experi- 
mentalists have sometimes used the comparison of the harometri- 
cal mean pressure: this process is capable of much precision, 
as M. Ramond has demonstrated, if we stop at the mean pres-~ 
sures of the same hours, in order to avoid the effects of the pe- 
riodical variations. In order to determine the relative altitudes 
of the levels of the South Sea and of the Atlantic Ocean, it 
ought therefore to be sufficient to compare the mean heights of 
the barometer over the two opposite coasts of America, M. 
Humboldt’s Journal furnishes us with the necessary data for this 
purpose. 
- In fact, we there find in the first place that at Carthagena and 
Cumana in the Gulf of Mexico, the mean pressure of the ba- 
rometer = 0-7620 millimetre by a temperature of 25° centi- 
grade. At the harbour of Vera Cruz, the thermometer being 
at 20° the height = 0-7613 millimetre, but corrected from the 
dilatation of the mercury, it becomes as at Cumana 0-7620 
millimetre. At the temperature of zero and at the level of the 
Atlantic Ocean, between the tropics, the mean height of the ba- 
rometer is consequently = 0:7585 millimetre. 
On the shores of the South Sea, at Callao, a port of Lima, 
M. de Humboldt found the barometer = 0:7606 millimetre, 
the thermometer 20°; and at Acapulco, still on the Pacific Ocean, 
the barometer =0-7617 millimetre, the thermometer 27°. 
These heights brought to the temperature of zero, yield for 
the mean pressure of the air at the level of the South Sea 0°7578 
millimetre. If the slight difference which we remark between 
this number and that which represents the mean pressure at the 
level of the Atlantic Ocean could not be attributed to the errors 
inevitable in such delicate observations, it will result that the 
South Sea must be higher than the Ocean by about seven metres. 
Other observations of M. Humboldt which have not yet been 
published, will give a difference a little greater and in the same 
proportion; but this celebrated, traveller who only used his ba~ 
Vol. 47. No. 217, May 1816, Aa rometers 
7 
