382 Mr cavendishV Account of 
than in the latter; for the error in the fettling of the 
quickfilver can proceed only from the adhefion of its 
edge to the fides of the tube; now the latter is affedled 
by the adhefion in two legs, and the former by that in 
only one : and, befides, as the air has neceffarily accefs to 
the lower leg of the fyphon barometer, the adhefion of 
the quickfilver in it to the tube will moft likely be dif- 
ferent, according to the degree of drynefs or cleannefs of 
the glafs. It is true, as Mr. de luc obferves, that the 
ciftern barometer does not give the true preflure of the 
atmofphere ; the quickfilver in it being a little depreffed 
on the fame principle as in capillary tubes. But this does 
not appear to me a fufhcient reafon for rejecting the ufe 
of them. It is better, I think, where fo much nicety is 
required, to determine, by experiment, how much the 
quickfilver is depreffed in tubes of a given bore, and to 
allow accordingly. 
By fome experiments which have been made on this 
fubjedt by my father Lord Charles cavendish, the de- 
preflion appears to be as in the following table : 
Infide dia- 
meter of 
tube. 
Grains of 
quickfil- 
ver in one 
inch of 
tube. 
Depreff. 
of furface 
of quick- 
iilver. 
Tn fide 
diame- 
ter. 
Grains 
of quick- 
filver. 
DeprelT. 
of fur- 
face. 
Infide 
diame- 
ter. 
Grains 
ofquick- 
lilver. 
Dcprell. 
ot fur- 
face. 
> 6 
972 
,005 
>35 
33 1 
,025 
,20 
108 
,067 
,5 
675 
>°°7 
>3° 
243 
,036 
H5 
61 
,092 
A 
43 2 
,015 
> 2 S 
169 
>°5° 
,10 
27 
1,40 
Tho 
