694 Co/. roy’s Experiments for 
more or lefs denfe, by the addition or fubtraCtion of 
weight, expanded equally with quickfilver, when af- 
fected with the fame degrees of heat? According to the 
ratio that took place between the expaniion of quickfil- 
ver and air, above and below zero, I intended to regulate 
the barometrical equation already found, without re- 
garding the proportion of the bulb to the bore of the 
manometer; or in other words, without paying any at- 
tention to the aCtual expanfion of the air confined in that 
inftrument.. 
But after a great number of thefe firft experiments 
had been made, it was judged proper to compute the 
aCtual expanfion of 1000 equal parts of air in the ma- 
nometer, from a heat of 2 1 2 0 ; wherefore, in the lalt, the 
accurate capacity of the bulb, with refpect to the bore, 
was determined ; at the fame time that the original mode 
of comparing the thermometrical with the manometrical 
fpaces, was ftill adhered to. 
It is eafy to conceive in experiments of this very de- 
licate nature, part of which, namely thofe on air lets 
denfe than the atmofphere, were extremely difficult and 
even laborious, that mathematical exactnels was not to be 
looked for; and that, notwithftanding every poffible pre- 
caution was taken, irregularities w'ould occur. Thefe, 
however, were not fo numerous as might have been 
i expeCled,, 
