who, from a great number of experiments, made 
upon the cordileros, and at various other heights 
above the level of the fea, concluded, that the abfo- 
lute elafticity of the air, which he calls, “ the iu- 
4< tenftty of the da flic force,” ruuft be different 
at different elevations. His conjectures indeed about 
the caufefrom whence the difference might arife, are 
not the mod natural ; and in one point he was evi- 
dently miftaken : namelv, that he imagined the ab- 
folute elafticity to be conflant at every given eleva- 
tion ; and accordingly he hath traced the curve, 
which, according to his experiments, exhibits the 
laws of its variations from one height to another. 
This, it muff be confeffed, was tru fling his expe- 
dients too far, which were not made with the moff 
accurate inflrumcnts ; and this may have given oc* 
cafion to his learned countryman M. de la lande, 
to fuppofe that this curve may rather exhibit the de- 
viations of his experiments from the truth, than any 
thing which really obtains in nature W. His general 
hypothecs, however, of a difference of abfolute 
elafticity, in different parts of the atmcfphere, muji 
obtain, whenever the temperatures of fuch different 
parts are unequal , unlefs the effeft of the inequality 
of temperature were to be compenfated by the fyn- 
chronous unequal operations of fome other caufe. 
That it does in faft obtain, when the temperature 
is unequal, is proved* beyond a doubt, inftead of 
being refuted, by M. de luc’s experiments; and 
this is to be confidered, as a further inftance of their 
ex a ft agreement with the genuine conclufions of 
accurate theory. 
(r) ConnoifTance pour l’annee 1765, p. 215, 
When 
