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conveniency, which whoever is acquainted with the 
true State of mountainous Countries, muft needs be 
fenlible of, and that is the extream Difficulty of meet- 
ing at the Bottom of high Mountains with Plains large 
enough for a proper horizontal Stand, or Balls, to fuch 
a Triangle, as an accurate and knowing Obferver 
would think fatisfaflory to determine a conliderable 
Height, making even proper Allowances for the Air’s 
Refra&ion. 
Among the many Improvements in Natural Philo- 
fophy, which are owing to the Toriceliian Tube, one 
of the molt conliderable Inventions of the laft Century, 
it hath been thereby enriched with a new Method of 
meafuring the refpe&ive Heights of Places, and their 
Elevation above the Level of the Sea} a Method, 
which, although it mult be owned, that it hath not as 
yet, and perhaps, conlidering the Inconlfancy of the 
Air, hardly ever will be brought to an abfolute De- 
gree of Certainty, is yet in many Refpe&s preferable 
to the Trigonometrical one, as it hath alfo been found 
by Experience to come nearer the Truth, and leads us, 
by a new and lingular Scale, from the very Horizon of 
the Sea to the Tops of the higheft Mountains, a Di* 
fiance far beyond the Reach of Geometrical Inftruments. 
This new Method is grounded upon that effiential Qua* 
lity of the Air, its Gravity or Prelfure. As the Column 
of Mercury in the Barometer is counterpoifed by a 
Column of Air of equal Weight, fo whatever Caufes 
will make the Air heavier or lighter, its Prelfure will 
be thereby increafed, or lelfened, and confequently 
the Mercury rife or fall. Again the Air is more or 
lefs condenfed, or expanded, in Proportion to the 
Weight, or Force, which prelfes it: Hence it is, that 
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