the means of encreafing the Divifions of the Barometer ad //- 
bitum^^ a way free from fiich Objeftions, which finally he pro- 
duced before the R. Society at their meeting on Feb. -jd. 1 685 
J^. vet. The contrivance whereof is this. 
Figure 1. Tab. II. Reprefents the Glafs of this Barofcope : 
the CyUnder A may be of what Diameter you picafe, the 
bigger the better, but it need not be above 2 inches long, 
the Cane A D muft be fo long, that the upper part of tiie Cy- 
linder B may be 29 Inches fiich a part of the hight of 
the other Cane B C, as the weight or fpecifick Gravity of the 
Liquor that is to fill that Cane is to the Specifick Gravity 
of Mercury, below the line a bin the Cylinder A. The third 
Cylinder C may be as high as you pleafe above the Cylinder 
B, but is moll conveniently made, foas the fquare of the 
Diameter of the Cane B C be to the fquare of the Diameter 
of the Cylinders B or C/ which mull: be exaftly equall J as the 
rife of the Mercury in the Cylinder B,is to the whole Length 
of the Cane B C ; for in this cafe there will be nothing 
Superfluous, but the divifions enlarged to the utmoft advan- 
tage. 
As to the method of filling this Barofcope, though the In* 
vcntor hath not yet declared his own contrivance for the do- 
ing it, yet it will not be unnecefTary to fhcw here how it 
may be done. One way, ( and the beft that occurs at pre- 
ient; is to leavea fmall hole at the top cf the Cylinder A, 
and another near the top of the Cylinder B : tl us latter be- 
ing well ftopt, pour in as much Mercury, at the other hole 
in A, as fhall fill both Canes as high as t iie Level of the faid , 
hole - which done, ftop either by Htrnietical y fealing it, or ;| 
elfe by a dr p of leal- wax ( the giafs being tirii ground rough I 
to make it ftick >) the hole in A ; then opening the. hole in B, ;j 
draw oif as much of the Mercury of the Cane B C till it ' 
will runn no longer : which done, ftopp firmly the hole in B 
( which may be done as you pleafe, there being no preifurc 
againft you ) and you will have theCylinder A evacuated of j 
Air for your purpofe ; and the hight of the Mercury will be j | 
asisufual in the ordinary plaine and Whcck-Barometers. ]^ 
Then 
