XXXII EXPLANATION OF THE PLATES. 



have, befides, an elevation vv'hich facilitates their courfe. 

 Not only are the ices from which they proceed very con- 

 Cderably elevated over the Hemifphere, but the Poles have 

 themfclvcs a great elevation of foil. I ground this affertion, 

 in the firft place, on the obfervations of Tycho-Brhaé and 

 Kepler, who faw the fhadow of the Earth oval at the Poles,, 

 in central eclipfes of the Moon \, and on the authority of 

 Caffïniy who aiïigns fifty leagues more to the axis of the 

 Earth, than to its diameter in any other diredlion. In the 

 fécond place, I have on my fide authentic experiments, col- 

 ledled by the Academy of Sciences, but which have no 

 longer been referred to fmce the opinion became prevalent^ 

 that the Earth was flattened at the Poles. 



For example, it is well known, that in proportion as. 

 you afcend on a mountain, the mercury on the barometer 

 fubfides : now, the mercury finks in the barometer, in 

 proportion as you advance northward. It falls about one 

 line, in our Climates, when you afcend to an elevation of 

 eleven fathom. According to the Hiftory of the Academy 

 of Sciences, for 1712, page 4, the weight of one line of 

 mercury, at Paris, is equivalent to an elevation of ten fa- 

 thoms and five feet, whereas, in Sweden, you have to 

 afcend only ten fathom, one foot and fix inches, to make 

 the mercury fink one line. The Atmofphere of Sweden^ 

 therefore, is not fo high as that of Paris, and confequently 

 the ground of Sweden is higher. 



To thefe obfervations may be farther fubjoined, thofe 

 made by the Navigators of the North, who have always 

 feen the elevation of the Sun above the Horizon greater, 

 the nearer they approached to the Poles. It is impoflible 



to 



