254 On the Mean Temperature of' the 



na) * possess almost the same low temperature, so that we may 

 conjecture, that the coldest |)oint of the equator between 80° 

 west and 60" east longitude, is, in the great ocean between the 

 west coast of Africa and the east coast of America ; but, from 

 thence the terrestrial temperature increases rapidly to the east 

 and west. The same holds for the calculated temperatures of 

 the equator which, we have already observed of the pole, that 

 the formulae are perhaps not quite conformable to one another. 

 It is difficult to conjecture what can have produced a greater 

 terrestrial temperature in the low latitudes of the second meridian. 

 The circumstance of the equator in Africa, extending through 

 a large extent of country covered with sandy wastes, may be a 

 cause of the phenomenon ; but it is difficult to conjecture how 

 this could influence high latitudes. If we reflect that there are, 

 under this meridian, two active volcanoes (Vesuvius and Etna) ; 

 that Germany is studded with basalt and other igneous rocks; 

 that a greater or less number of warm springs testify the high 

 temperature of the interior ; that, finally, in the Tyrolesc Alps, 

 porphyry and augite-rock predominate, to which, according to 

 the new views, these immense masses owe their elevation ; it is 

 natural to be expected, that even this circumstance of melted 

 igneous masses being found at a small depth under the surface 

 of the whole district, may be connected with the higher tem- 

 perature of the soil. 



South of the equator we possess but one observation, that of 

 Congo, under the second meridian ; and if a single observation 

 can justify us in forming any conclusion, it explains how the 

 warmest isogeothermal line (or the isogeothermal equator) does 

 not coincide with the equator of the earth. We require only, in 

 the map, Plate IV., to halve the distance between the isogeother- 

 mal line of 77*0 and the point in Congo, where the terrestrial 

 temperature is also 77°, to find a point througli which the isogeo- 

 thermal equator must pass. If this line, as is probable, runs 

 parallel to the isogeothermal line of 77°, then is the temperature 

 on it greater under the first meridian, less under the second, and 

 likewise less under the third and fourth, than the calculated 

 temperature for the equator of the earth ; the temperatures are 

 therefore distributed similarly on the isogeothermal equator, as 



" Combining tlie observations at Philadelphia and Cnmana, we find only 

 79-92 for the teniperaliue at the equator. 



