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fubtangent of the atmofpherical curve, in roooths of 
an Englifh fathom, whatever be the value of n, then, 
8 x w 
when n = — 448,875, B — n= o 3 that is, the 
fubtangent vanifhes ; and the abfolute elaftic force, 
which is always as the fubtangent (by §. 4.) muft 
vanifh with it 3 but when n ■=. — 448,875 the tem- 
perature is — 409,13. 
Perhaps it may be thought more probable, that 
the variation of the fubtangent, or of the elaftic 
force, is not precifely as the variation of tempera- 
ture. If the fubtangent changes in a geometrical 
proportion while the temperature, as fhewn by the 
thermometer, changes arithmetically, the fubtan- 
gent, or the abfolute elaftic force, will not vanifh 
with any affignable decrement of temperature 5 and 
in that temperature, in which it fhould vanifh, ac- 
cords to M. de luc’s formula , it will ftill remain 
more than JL.ths of what it is in the temperature 
39,74 ; and yet the equation, for an increment 
or decrement of temperature, amounting to 40°, 
will not differ from M. de luc’s by more than four 
fathom in the height of 1000. I muft repeat, that 
I am now only pointing out the conclufions of 
theory, as hints of further enquiry. I do not mean 
to fubftitute this hypothecs as more accurate than 
M. de luc’s in practice 3 I do not affirm, that it is 
more true in theory. I mean only to foggeft, that 
if M. de luc’s formula are admitted as mathe- 
matically true, a confequence will follow, which 
may feem to fome unlikely to obtain in nature. 
That however this confequence, if otherwife im- 
probable (which is not the opinion to which, for, 
my 
