of pretty hard Cement, by heat made very soft, I press it into the hole
E, and thereby stop it very fast; and to secure this Cement from flying
out afterward, I bind over it a piece of Leather, that is spread over
in the inside with Cement, and wound about it while the Cement is hot:
Having thus softned it, I gently erect again the Glass after this
manner: I first let the Frame down edge-wayes, till the edge RV touch
the Floor, or ly horizontal; and then in that edging posture raise the
end RS; this I do, that if there chance to be any Air hidden in the
small Pipe E, it may ascend into the Pipe F, and not into the Pipe DC:
Having thus erected it, and hung it by the hole Q, or fixt it
perpendicularly by any other means, I open the end F, and by a small
_Syphon_ I draw out the _Mercury_ so long, till I find the surface of
it AB in the head to touch exactly the line XY; at which time I
immediately take away the _Syphon_, and if by chance it be run somewhat
below the line XY, by pouring in gently a little _Mercury_ at F, I
raise it again to its desired height, by this contrivance I make all
the sensible rising and falling of the _Mercury_ to be visible in the
surface of the _Mercury_ in the Pipe F, and scarce any in the head AB.
But because there really is some small change of the upper surface
also, I find by several Observations how much it rises in the Ball, and
falls in the Pipe F, to make the distance between the two surfaces an
inch greater then it was before; and the measure that it falls in the
Pipe is the length of the inch by which I am to mark the parts of the
Tube F, or the Board on which it lyes, into inches and Decimals: Having
thus justned and divided it, I have a large Wheel MNOP, whose outmost
limb is divided into two hundred equal parts; this by certain small
Pillars is fixt on the Frame RT, in the manner exprest in the Figure.
In the middle of this, on the back side, in a convenient frame, is
placed a small Cylinder, whose circumference is equal to twice the
length of one of those divisions, which I find answer to an inch of