( 170 ) 
After I had contriv’d the Machine, as above men- 
tioned, I conlider’d, that as the Tube is of a very fmall 
Bore, if the Liquor fhou’d rife into the Ball A, in car- 
rying the Inftrument from one Place to another, fome of 
it wou’d (tick to the Sides of the Bali A, and that upon 
its Defcent in making the Experiment, fo much might 
be left behind, that the Liquor wou’d not be high e- 
nough at D, to lhew the Difference of Level j there- ' 
fore, to prevent that Inconveniency, I have contriv’d a 
blank Screw to fhut up the Hole at A (Fig. IV. and V.) 
as foon as one Experiment is made, that in carrying 
the Engine, the Air in A may balance that in C, fo 
that the Liquor (hall not run up and down the Tube, 
whatever Heat and Cold may ad upon the Inftrument, 
in going from one Place to another. 
Now, becaufe one Experiment being made in the 
Morning, the Water may be fo cold, that when a fe- 
cond Experiment is made at Noon, the Water cannot 
be brought to the fame Degree of Cold that it had in the 
Morning j therefore in making the firft Experiment, 
warm Water muft be mix’d with the Cold • and when 
the Water has flood fome time, before it comes to be as 
cold, as it is likely to be at the warmed Part of that Day^ 
obferve, and fet down the Degree of the Thermometer, 
at which the Spirit {lands *, and like wife the Degree of 
the Water in the Barometer at D then fcrew on the 
Cap at A, pour out the Water, and carry the Inftru- 
ment to the Place whofe Level you wou’d know } 
there pour in your Water, and when the Thermome- 
ter is come to the fame Degree as before, open the 
Screw at Top, and obferve the Liquor in the Baro- 
meter.. 
My Scale, for the Barometer, is ten Inches long, and 
divided into Tenths, fo that fuch an Inftrument will 
ferve for any Heights not exceeding ten Feet, each 
Tenth 
