[ 6r ] 



I call that flate the natural flate of the atmofphcre in which 

 the barometer on the level of the fea would ftand at 30 inches 

 in ferene weather, conformably to the fifth obfervation. To 

 produce this ftate, the weight of the atmofphere muft be every 

 where equat at the furface of the fea. The weight of the atmo- 

 fphere proceeds from its denfity and height ; therefore, to pro- 

 duce this equality of weight, it fhould be loweft where its den- 

 fity is greateft, and higheft where its denfity is Icaft. Thefe ex- 

 tremes of denfity take place in the agquatorial and polar regions. 

 Under the aequator, the centrifugal force, the diftance from the 

 centre of the earth, and the heat, are all at their maximum ; in the 

 vicinity of the poles, on the contrary, they are at their minimum. 

 Therefore, if the height of the 51 be 30 inches under the aequator 

 and under the poles, the atmofphere muft be higheft under the 

 a?quator, and loweft under the poles, with feverai intermediate 

 gradations. 



But though the asquatorial air be lefs denfe to a certain height 

 than the polar, yet at certain greater heights it muft be more 

 denfe ; for the mercurial heights at the level of the fea being 

 equal, the maffes of the correfponding atmofpheric columns muft 

 be equal ; but the lower part of the zequatorial column being 

 more expanded by heat, &c. than the correfponding fedion of 

 the polar column, its mafs muft alfo be fmaller than that of the 

 correfponding fedion of the polar column ; therefore a propor- 

 tionably greater part of its mafs is found in its fuperior fedion 

 than is found in the fuperior fedion of the polar column ; 

 therefore the lower extremity of the fuperior fedion of the sequa- 

 torial column is more comprefi'ed, and confequently denfer than 



the 



