5^2 Sir george shucksurgh’s Obfervations 
I have thus endeavoured to fhew then that the error 
of the theory is — ^ 411 ^ when the temperature of the 
air is 6 i°. 4 (fee the table of the refult of the obferva- 
tions). It remains therefore, finally, that we deduce a 
rule, the error of which fhall be nothing, viz. to find 
the temperature wherein the difference of the loga- 
rithms of the heights of the barometer, taken to four 
places of figures, will give the true difference of eleva- 
tion in Englifh fathoms. Previous to this invefligation, 
with which I intend to conclude this paper, it will be ne- 
ceffary to remark, that by repeated experiments with the 
barometer, I find a fmall difference in the equation for 
the expanfion of air by a change of temperature, and 
even in that of quickfilver from the fame caufe, from 
what Mr. de luc’s obfervations have given iS a> . I fhall 
s< approchante de celle, qu’u n grand nombre d’obfervations du barometre dans 
“ les Cordelieres ont didte depuis a M. bouguer : cependant malgre l’appui 
** 1 ue ces experiences fe pretent reciproquement, on verra qu’elies etoient encore 
“ bien eloignees de fournir une regie generale.” Recherches fur l’Atmofphere, 
left. 267. 
( a ) He indeed made his experiments on the atmofphere itfelf with the 
barometer, in order to determine the variations of its denfity ; but fince it 
appears that the abfolute denfity of this fluid is different from what he flip- 
ped it, it is no bold conjefture to prefume that the degree of its variation 
fhould be different alio; and to afcertain this point, I have preferred the 
inftrument above-mentioned to the method ufed by Mr. de luc, how direft 
foever his may feem; for in determining minute quantities or equations, we 
muff not embarrafs ourfelves with the compound effedt of too many caufes at a 
tisae. 
wot 
