mid the Distrihtitmi of Heat over the 'Globe. 270 
The last give for the 
Gent. 
T^ahr. 
Metres. 
Equinoctial zone, 
1° 
or 1°.8 
190 
Parallels of 45° — 47°, 
1 - 1° 
or 1°.8 
160—172* * 
This agreement is no doubt very remarkable, and the more 
so, as, in comparing stationary with insulated observations, we 
confound the mean state of the atmosphere in the course of a 
whole year with the decrease which corresponds to a particular 
season, or a particular hour of the day, M. Gay-Lussac found, 
in his celebrated aeronautical voyage from 0 to 7000 metres, 
(0 to 22,960 feet), a centigrade degree for 187 -metres, near Pa- 
ris, at a period when the heat of the plains was nearly equal to 
that of the equinoctial region. It is on account of this observed 
equality in the decrease of heat, in reckoning from the standard 
temperature of the plains, that the astronomical refractions cor- 
responding to angles below 10°, have been found the same un- 
der the equator and in temperate climates. This result, con- 
trary to the theory of Bouguer, is confirmed by observations 
which I have made in South America, and by those of Maske- 
lyne at Barbadoes, calculated by M. Oltmanns. 
We have seen, that between the tropics, on the back of the 
Cordilleras, we find, at 2000 metres of elevation, I will not say 
the climate, but the mean temperature of Calabria and of Sicily. 
In our temperate zone, in 46° of Lat. we meet at the same eleva- 
tion with the mean temperature of Lapland -f-. This comparison 
temperature of ^October is even a little below that of the whole year, it is probable 
that the height of the plain of Great Thibet exceeds from 2900 to 3000 metres. — 
See my Memoir on the Mountains of India in the Ann. de Chim. et de Phys. 1817. 
the Editor. 
As the cold meridian of the globe passes through the plains of Great Thibet, 
we conceive that the mean temperature of Lat. 29° in that plain, when reduced to 
the level of the sea, will be about 05°, and therefore that the height of the plain of 
Great Thibet will not exceed 2800 metres or 9184 feet. — D. B. 
* Saussure gives for the summer 160 metres, (525 feet) ; for winter 230, (754 
feet) ; and for the whole year 195, (640 feet). M. Ramond gives 165, (538 feet), 
M. D’Aubuisson 173 metres, (567 feet). — ^See Journ. de Phys. tom. Ixxi. p. 37. ; 
De la Formul. Barometr. p. 189. ; and my Recueil d'Obs. Astron. tom. i. p. 129. 
*|* As the temperature varies very little in the course of a whole year in the 
equinoctial zone, we may Term a pretty correct idea of the climate of the CordiL 
