70 Analyses of Books. [Jan. 



Terrestrial Heat. — The facts with which we are at present ac- 

 quainted tend to prove that every place on the surface of the globe 

 has an invariable mean temperature. The mean temperature of the 

 equator is between 81*5 and 82° 4, being modified by the great extent 

 of the equatorial seas. The entrepid northern navigators have found 

 a great difference, in the same latitude, between the temperatures 

 on land and in the open sea. At Melville I d - the mean heat was 

 — 18° 5C, while in the open sea it was — 8° 3. Calculating from 

 these data, the temperature of the pole would be — 25° or — 30°. 



It is remarkable that those places which are situated on the same 

 isothermal line do not present the same vegetable productions. 

 Hence, some have divided climates into constant, where the tem- 

 perature is steady during the year, variable, and excessive, which 

 comprehend those where the differences are very great. Cassini, in 

 1671, had remarked that under the Observatory of Paris, the tem- 

 perature was steady during the whole year ; and the observation has 

 been confirmed, the heat being determined to be 11° 82 (53° F.) 

 Cordier has inferred, from his researches on the temperature towards 

 the interior of the earth, that below a particular point where the 

 temperature is steady, the heat increases with the depth, to the 

 amount of 1° for every 25 to 30 metres. 



M. Fourier has demonstrated that the cooling of the globe, if 

 such a fact is admitted, must be very slow, being less than ^-^ 

 of a centigrade degree for a century ; and he has drawn these conse- 

 quences : 1. All the heat below a particular point where the tem- 

 perature is steady, has been possessed by the earth from its com- 

 mencement. 2. This heat is intense in the nucleus, and at a certain 

 distance from the centre it begins to diminish by regular laws up to 

 the steady point. 3. The internal equilibrium changes with time, 

 and will continue to alter until the whole heat is dissipated, but this 

 process is going on in an extremely tardy manner. 4. The heat de- 

 rived from the interior cannot appreciably modify that of the surface. 



Humboldt has observed that in Mexico the decrease of tempera- 

 ture is not proportional to the height ; and Boussingault has found 

 that in twenty-three years the sources of the Mariara have increased 

 in temperature from 59° 3 C. to 64° ; and those of Strincheras, from 

 90° 4 to 92° 2. The diurnal variation of the thermometer at the 

 equator on the sea is 1° to 2° , while on the continent it is 5° to 6°. 

 At the equator the ocean's surface is hotter than the air ; but at the 

 poles the reverse is the case.* Between the tropics, the heat dimi- 

 nishes with the depth ; on the polar seas it diminishes as we descend. 



Such are some of the principal circumstances bearing upon terres- 

 trial heat with which we are at present acquainted . 



The formations of which the globe is composed is the next subject 

 which our author takes up, after speculating upon the method in which 

 it was consolidated, applying known agents to the explanation of vol- 

 canic phenomena, and tracing out a sketch of the facts which have 

 been ascertained in reference to terrestrial heat. He first notices allu- 



* In lat. 2° 9' N., long. 20° 38 W., I found the temperature of the Atlantic 

 Ocean 79<>r>, that of the air being 79° ; and in 2*20 S.L^ 59<>5' E.L. the thermo- 

 meter stood in the air at 80°, and in the Indian Ocean at 88°6. — Edit. 



