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And here it is plain in the firfl place, that, as both are of equal 

 weight, the intra-tropical column, being more expanded by heat, muft 

 reach to a greater height than the colder and lefs expanded extra- 

 tropical air. But that at a certain height the weight and denfity of 

 the intra-tropical air muft be confiderably greater, and confequently 

 that this air muft flow over or into the other, will now appear by 

 fticwing the elevation that mercury would ftand at in each, at 

 that given height. The height I now allude to is that of the upper 

 line of congelation ; in the mean of the above-mentioned lati- 

 tudes of the extra-tropical air, this height is 2i8co feet = 3633 

 fathoms, which, fubtra6ted from log. 30 (= 4771212) gives the 

 logarithmic number 113S212; and this correfponds with the na- 

 tural number 12,997, ^' ^° ^^'^ height, the mercury would then 

 rife in the barometer. But in the column reprefenting the I'ntra- 

 trop'ical air, the mercury would rife at the fame elevation over the 

 earth to 13,835 inches, as appears by the following calculation. 

 The mean height of the line of congelation of the intra-tropical 

 air is 25000 feet, and the mean heat of this air, at the furface of 

 the earth being 87*^, the difference of this with 32° is 55°, which 

 divided by 250,00 quotes 0,222 the common difference of the 

 progrefficn ; and^ this multiplied into 21800 (218,00 being ex- 

 preffed in the terms of the progreffion) gives the diminution of 



heat 



