( II )

The Cylinder A t may be of what Diameter you please, the bigger thebetter, but it need not be above two inches long, the Cane A D, must be solong that the upper part of the Cylinder B, may be 2g inches 4 - such a pari ofthe height of the other Cane B C, as the weight or fpecifickGravity of theLiquor that is to fill that Cane is to the specisick Gravity of Mercury, below theline A B, in the Cylinder A. The third Cylinder C, may be as high as youplease above the Cylinder B, but is most conveniently made, so as the squarcof the Diameter of the Cane B C, be to the square of the Diameter of the Cylin-ders B, or C, (which must be exactly equal) as the rise of the Mercury in theCylinder B, is to the whole length of the Cane B C: for in this case there willbe nothing soperfluous, but the divisions enlarged to the utmost advantage.

As to the method of filling this Baroseope, though the Inventor hath notas yet declared his own conrrivance for the doing it, yet it will not be un-necessary to Ihew here how it may be done.^One way, fand the best that oc-curs at present) is to leave a small hole at the top of the Cylinder A, and a-nother near the top of the Cylinder B : this latter being well stopt, pour in asmuch Mercury, at the other hole in A, as shall fill both Canes as high as thelevel of the said hole ; which done, stop, either by Hermetically sealing it, oreise by a drop of Seal-Wax \ the Glass being first ground rough to make itstick ) the hole in A ; then opening the hole in B, draw off as much of theMercury of the Cane BC till it will tun no longer : which done, stop firmlythe hole in B (which may be done as you please, there being no Pressure a-gainst you ) and you will have the Cylinder A, evacuated of Air for your pur-pose j and the height of the Mercury will be as is usoal in the ordinary plainand Wheel Barometers. Then pour into the Cane B C as much Spirit ofWine tinged with Cochineele, and Oil of Turpentine, equal parts of each, as(hall stand above the surface of the Mercury so many feet as you make the en-larged scale of your Barometer, or as is between the middle of the Cylinders Band C, and you will find the Mercury sink in the Cane B C, and rise iirthe otherCane A D, in such proportion, that each 13 foot of Oil and Spirit, will raisethe Mercury ten inches: This done, you must pour on, by the Cane B C, somuch Mercury as may fill up the Cylinders A, and B, to such heights, consideringthe present weight of the Atmosphere, that the surface of the Mercury in both,may at the utmost Limits, (which have not in England been found to exceed30 ,6 and 28,6 inches ) always fall within the bedies of the Cylinders, andnever enter into the Canes.

Here note, That these Liquors are chosen upon two accounts; First, theyare «exceeding near of a weight, and Spirit or Wine highly rectified is some-what lighter than Oil of Turpentine, but by a very small Addition ofPhlegm or Watcr, the Spirit will preponderate and be undermost; so thatyou may make them as near of a weight as you please, and conscquently aCylinder of the Oyl inftnfibly difiering from an equal Cylinder of Spirit ofWine. Secondly, they are Liquors that will not mix ; so that the Oyl of Turpen-tine swimming on the top, will be divided by a line only from the tingedSpirit of Wine, which the Oyl will keep from evaporating.

The Effect of this Baroseope will be, that when the Atmosphere is heavy,

C 2 and

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