-( 1 66 ) 
Dr* Halley , fome Years ago, publifh’d two Tables to 
fhew, how much the Mercury in the Barometer wou’d 
fubfide, when the Iaftrument is carried up to determi- 
nate Heights, above the Level of the Place where the 
firft Obfervation was made ^ but as he makes only one 
Tenth of an Inch of Fall of Mercury , to correfpond with 
an Height of 90 Feet (which Height is rather of the 
lead) it is evident, that only very high Hills and Moun- 
tains can have their Heights determin’d by this Method. 
The fame learned Profelfor has lately, in the Thilofo- 
phical TranJatUons , propofed Mr. Patrick' s pendent 
Barometer for taking the Level of diftant Places, be- 
caufe the Mercury , in the Tube of the faid Barome- 
ter, does fometimes rife and fa'l a Foot, ora Foot and 
an Half} if therefore the Motion of the Mercury in this 
Barometer, be five times more fenfible than in the com- 
mon one, a Tenth of an Inch of Fall of the Mercury , 
will anfwer to an Height of iB Feet •, and therefore fuch 
an Inftrument might be of Ufe in taking the Levels of 
diftant Places. But I know by many Experiments, that 
this won’c anfwer in Pra&ice} becaufe as the Tube of 
fuch a Barometer is of a very ftnall Bore, the Attrac- 
tion of Cohefion, whereby the Mercury is apt to ad- 
here to the Tube, will difturb the Motion of the 
Mercury caus’d by the different Preffure of the At- 
mosphere } fo that fetting up this Barometer feveral 
Times fucceffively in the fame Place, it will often dif- 
fer a Tenth of an Inch, or more } and if it be fliaken, as 
is commonly done to fet it right, the Mercury will 
fometimes part, and a Drop of it fall from the reft *, fo 
that it is lefs to be depended upon forthis Ufe, than the 
common Barometer. 
Mr. Stephen Gray has often made a very fenfible 
Barometer in the following Manner. Into a Bottle C B, 
'Fig. I.) he fixes a Tube A B, of a very fin all Bore, 0- 
* pen 
