The Figure is thus: And the demonstration is by the [12 e vij], as afore: but here is to be added the height of the measurer; which if it be 4 foot, the whole height shall be 76 foote.
Therefore in an eversed altitude
11. If the sight be from the beginning of the Index parallell to the height, as the segment of the transome
is, unto the segment of the index, so shall the length given be, unto the height sought.
Eversa altitudo, An eversed altitude (Reversed, H:) is that which we call depth, which indeed is nothing else, in the Geometers sense, but heighth turned topsie turvie, as we say, or with the heeles upward. For out of the heighth concluded by subducting that which is above ground, the heighth or depth of a Well shall remaine.
Let the segment of the transome ae, be 5 parts: the segment of the Index ei, be 13: the diameter of the Well (which now standeth for the length:) be 10 foote, which at toppe is supposed to be equall to that at bottome: the opposite height, by the [12 e vij], and the golden rule shall
be 26 foote: From whence you must take the segment of the Index reaching over the mouth of the Well: And the true height (or depth) shall remaine; as if that segment of 13 parts be as much as 2 foote, the height sought shall be 24 foote. The second manner of measuring of heights followeth.
12. If the sight be from the beginning of the Index perpendicular to the heighth to be measured, as the segment of the Index is unto the segment of the Transome, so shall the length given be to the heighth.