of the Terrestrial Globe, 219 



VII. Can the variations which certain astronomical elements under' 

 go, sensibly modify terrestrial climates 9 



There is upon the globe but a single region, where, allowance 

 being made for the atmospherical refractions, the days and nights 

 have at all times an equal duration. This region bears the 

 name of the terrestrial equator. 



Everywhere else except in the terrestrial equator, the days 

 and nights have in general unequal lengths. At Paris, for ex- 

 ample, on the 21st of June, the day consists of sixteen hours, 

 and the night of eight. On the 21st of December, on the con- 

 trary, the day consists of eight, and the night of sixteen. The 

 20th and 21st of March, and the 22d and 23d of September, 

 are the only epochs, when there, the days and nights consist 

 exactly of the same number of hours. The latter dates (the 

 20th of march, and the 22d of September) have this peculiarity, 

 that then there is in all places of the earth, from pole to pole, 

 and from east to west, a perfect equality between the time of 

 the sun's presence above the horizon, and below it. 



It is not necessary that we should minutely have studied thef 

 difficult question of terrestrial temperatures, that we may in 

 general comprehend that, under all latitudes, the epoch of long 

 days and short nights shall prove a time of high temperature ; 

 and of long nights and short days, on the contrary, of low tem- 

 perature ; that, in short, the thermometric extremes shall \ti 

 every place have an intimate and necessary connexion with days 

 of a long and of a short duration. Every cause which reduces 

 this difference will make the summers and the winters less 

 unlike. It is not altogether so evident, that from the same 

 cause will result a change in the mean temperatures ; but a cer- 

 tain equalization of seasons will so clearly ensue, and will be so 

 capable of every where modifying the phenomena of vegetation, 

 that it would be useless to examine, whether, since the records 

 of history, this equalization be the result of a change of the 

 form and of the position of the solar orbit. 



A circle which makes the entire circuit of the heaven, and 



this is no slight effect of heat, when compared to the hundreds and the thou- 

 sands of degrees of cold which probably prevail in the space uninfluenced by 

 h at cause with which M. Fourier is engaged. 



