(4) 
jjgainft the top, as it dahceth up and down, which endangers 
breaking off the top oFthe Tube. The bottom of the Tube I 
would have ground aflant near half an Inch^ that the bottom 
of the Tube touching the bottom of the Ciflern, the Orifice 
thereof may lye about the middle of the Mercury in the Ci- 
fkrn : which will prevent the Air getting into the Tube, by 
reafon the Afcr^wr/ is always about che Mouth of the Tube. 
The Ciftern muft be mads wide^ either of Glafs, or clofe- 
grained Wood ; round ths Bri n of which, on the out-fide, 
mufl be a Notch ro tye on the Leather that is to cover ir. 
When the Tube is filled, cleared of Airland plunged into the 
Ciftern near fall of Msrmry^ enclofe the Mtrcury with gentle 
Leather tied very fafl round the Tube near the bottom, 
which being fpread over the Ciftern, tie it round that alfo : 
The Tube and Ciflern, thus conjoin' d with Leather, muft 
bs lodg'd m a Cafe, made very fit to receive both, where 
they muft lye very faft. Thro' the Cafe let three or four 
Holes be bored, to let the Air in freely to the Leather that 
covers the Ciftern, which lying clofe againft the Holes, will 
firmly enough keep the Mercury from running out at them. 
The whole Inftrument thus prepared, muft be lufpended 
on the Top : For which purpofe a Tripos may be beft, whofe 
Legs open and ftiut by Joynts at the Top. 
The Weather-plates ^re to be put upon the Frame, by let- 
ting them to the fame height, at which th^ Mercury ftands in 
a common Barometer. 
That the whole may be better apprehended, I have annex- 
ed the following Figure 9, In which 
A. A. A. A. Is the Tripos. 
B. B. B. The Frame or Cafe, with the Barometer and Ciftern in ir, 
reprefented by prickt Lines. 
C. C. The Weather-plates. 
Vig, 10. Reprefenteth a Tube communicated to me by a Friendi 
which ferveth for the more nice meafuring the height of the Mercury : 
For an Inch of perpendicular height, may be made 2 or 3, by bending 
the Tube more or lefs. This Tube may be crooked at 28 Inches length, 
for common ufe ; but at 23 or 24 Inches for greater heights, as Snowdon 
for higher Hillsj on which it defcended lo 26,1 Inches in Mr, HaBe/s 
Obfervations. 
a The head of the Tube, with its narrow Neck, to bridle the Blow 
of the Mercury, as before diredled, 
b The bottom ground aflant, as was before directed, 
cThe Crook. 
4 d The Weather Plates. IL A 
