( »70 ) 
The manner of ding it is thus : Holding the Qua* 
drant in a vertical Pofture, with that Limb to which 
the Level is fixed parallel to the Horizon, raife the 
Index to fome Divifion of the Arch, as near as you 
can to the true Height of the ObjeQ: ; which is fup- 
pofed to be near the Meridian, and confequently to 
alter its Altitude but flowly: Then turning the Key 
of the Stop-cock, fo as to let the Spirit of Wine pafs 
through the fmall Hole in it, keep the Image of the 
Objed as clofe to the Thread on the Vane as you can, 
endeavouring that the unavoidable Vibrations of it 
above and below the Thread, may be equal, both in 
refped of their Length, and the Swiftnefs of their 
Motions, Continue this ’till the Spirit feems quite 
fettled to fome Part of the Scale, and fomething lon- 
ger. This it will do flowly, but without any fen- 
fible Vibrations j for the Stop-cock allowing it no 
Paffage but through the fmall Hole in its Key, will 
give fuch a Check to itsMotions,as not only to flop thofe 
Vibrations,but alfo to hinder its being thro wnback wards 
and forwards in theTube by any Shocks of the Inftru- 
ment ; and yet as far as I have obferved will not pre- 
vent its fettling (with fufficient Truth, though flow- 
ly) to the loweft Part of the Tube. About half a 
Minute of Time or more may be neceflary for this, 
according as the aforefaid fmall Hole is greater, or lefs 
in Proportion to the Bore of the Tube. When you 
judge the Spirit quite fettled, turn the Stop-cock again : 
It is of no Importance that the Image of the Objed 
be exaftly on the Thread at the Inftant that this is 
done. Obferve againft what Degree, and Part of a 
Degree, each End of the Spirit in the Tubeftands. If 
your Scale be number’d like., the upper one in the 
Figure, and the Quantity of Spirit be exaft, both 
Ends 
