460 COSMOS. 



greatest velocity. The reassuring solution of tins problem is 

 to a certain extent contained in the beautiful law first pointed 

 out by Lambert,* 8 according to which the quantity of heat 

 which the Earth receives from the Sun in each part of the 

 year, is proportional to the angle which the radius vector of 

 the Sun describes during the same period. 



As the altered position of the major axis is capable of 

 exerting only a very slight influence upon the temperature of 

 the Earth ; so likewise the limits of the probable changes in 

 the elliptical form of the Earth's orbit are, according to Arago 

 and Poisson,* 5 so narrow that these changes could only very 



43 " II s'ensuit (du theore*me du a Lambert) que la quan- 

 tite de chaleur envoyee par le Soleil a la Terre est la mme 

 en allant de I'equinoxe du printems a. 1'equinoxe d'automne 

 qu'en revenant de celui-ci au premier. Le terns plus long 

 que le Soleil emploie dans le premier trajet, est exactement 

 ompense par son eloignement aussi plus grand ; et les quan- 

 tites de chaleur qu'il envoie a la Terre, sont les memes pen- 

 dant qu'il se trouve dans 1'un ou 1'autre hemisphere, boreal 

 ou austral." -Poisson, Sur la Stabilite du Systeme Planetaire^ 

 Connaissance des Temps for 1836, p. 54. " It follows from the 

 theorem of Lambert, that the quantity of heat which is con- 

 veyed by the Sun to the Earth is the same during the passage 

 from the vernal to the autumnal equinox as in returning from 

 the latter to the former. The much longer time which the 

 Sun takes in the first part of its conrse. is exactly com- 

 pensated by its proportionately greater distance, and the 

 quantities of heat which it conveys to the Earth are the same 

 while in the one hemisphere or the other, north or south." 



44 Arago, op. cit. pp. 300-204. 4i L'excentrieite," says 

 Poisson, (op. cit. pp. 38 and 52,) " ay ant toujours etc et 

 devant toujours demeurer tres petite, 1'influence des variations 

 seculaires de la quant ite de chaleur solaire re^ue par la Terre 

 sur la temperature moyenne parait aussi devoir etre tres 

 limitee. On ne saurait admettre que 1'excentricite de la 

 Terre, qui est actuellement environ un soixantieme, ait jamais 

 ete ou devienne jumais un quart, comme culle de Junon ou 



