Dear all,
I am facing an ivory portable altitude sundial datable to the late 16th
century. His drawing is very similar to the one shown by Cristoforus
Clavius, at page 647 of his work "Gnomonicae libri octo".
On the back of it there are two scales of the "umbra recta"(horizontal) and
"versa" (vertical). They are two styles, one called "quadrato geometrico per
misurare ogni lunghezza" (geometrical square to measure every length) and
divided in 60 & 60 parts. The second one is called "Scala altimetra di gradi
100 per misurare ogni altezza da lontano" (Altitude scale of 100 degrees, to
measure every far height) and divided in 12 &12 partitions. This second
scale carries on the border of the quadrant a partition in 100 degrees fit
in a squared angle (centesimal degrees).
Well, there is a thing that I don't know, and I would like to understand.
I know that altitude scales for horizontal and vertical shadows are usually
divided in twelve, why the first one is divided in sixty both sides?
Why the existence of the centesimal partition, when usually were ninety?
And more, why draw two different scales to measure height and length when
usually is enough only one?
Is there some one that may help me in the knowing of this puzzled matter?
Regards
Mario
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Mario Arnaldi
Viale Leonardo, 82
48020 LIDO ADRIANO - Ravenna
Italy
E-Mail [EMAIL PROTECTED]
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