Dear Mario, In my experience as a curator, I have seen many 16th century scientific instruments with shadow squares--including surveying instruments, quadrants, astrolabes, and sundials--in which the scales are divided into 60, 100, or other numbers of parts. I believe that this was done for greater accuracy in the calculations.
Happy Holidays, Sara Sara Schechner Genuth, Ph.D. Gnomon Research __Curators on Call __Outreach Professionals 1142 Loxford Terrace Silver Spring, MD 20901 301-593-2626 (tel/fax) [EMAIL PROTECTED] > > 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 +ACI-Gnomonicae libri octo+ACI-. > On the back of it there are two scales of the +ACI-umbra > recta+ACI-(horizontal) and > +ACI-versa+ACI- (vertical). They are two styles, one called +ACI-quadrato > geometrico per > misurare ogni lunghezza+ACI- (geometrical square to measure every length) and > divided in 60 +ACY- 60 parts. The second one is called +ACI-Scala altimetra > di gradi > 100 per misurare ogni altezza da lontano+ACI- (Altitude scale of 100 degrees, > to > measure every far height) and divided in 12 +ACY-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 > --------------------------------------------------------- > Mario Arnaldi > Viale Leonardo, 82 > 48020 LIDO ADRIANO - Ravenna > Italy > E-Mail marnaldi+AEA-linknet.it > --------------------------------------------------------- >
