J. R. Mayer on Celestial Dynamics. 409 
is however, closely connected with the changes on the earth's 
surface. 
earth cannot comport itself differently from any other mass, 
however small it be. In spite of the heat which it receives from 
th I 
of its surface. Between the tropics the mean temperature pro- 
duced by the sun is about 28°, and the sun therefore is as little 
able to stop the cooling-tendency of the earth as the moderate 
warmth of the air can prevent the cooling of a red-hot ball sus- 
pended in a room. 
_ Many phenomena—for instance, the melting of the alae 
near the bed on which they rest—show the uninterrupted emis- 
sion of heat from the interior toward the exterior of the earth; 
and the question is, Has the earth in twenty-five centuries ac- 
tually lost no more heat than that which is requisite to shorten a 
radius of more than six millions of metres only 15 centimetres? 
In answering this question, three points enter into our calcu- 
lation :—(1) the absolute amount of heat lost by the earth in a 
certain time, say one day; (2) the earth’s capacity for heat; and 
(3) the coéfficient of expansion of the mass of the earth. _ 
As none of these quantities can be determined by direct 
measurements, we are obliged to content ourselves with probable 
estimates; these estimates will carry the more weight the less 
they are formed in favor of some preconceived opinion. 
_ Considering what is known about the expansion and contrac- 
tion of solids and liquids by heat and cold, we arrive at the con- 
clusion that for a x reli Si of 1° in temperature, the linear 
contraction of the earth cannot well be less than saute part, a 
een which we all the sp sos adopt because it has been 
ised by Laplace, Arago, and others. oe 
ast i moaned fa cmt for heat of all solid and liquid 
bodies which have been examined, we find that, both as regards 
Am. Jour. ~~ Serres, Vou. XXXVIII, No. 114.—Nov., 1864 
