Re: Drinkwater construction help request

[Ronald W Doerfler]

The distance from D to the "zodiacal circle" is arbitrary, because all
you really are doing is fixing the angles of the line segments radiating
out from D.  You want the outer lines to be +/-23.5 degrees from the
horizontal from D.  The interior lines have angles derived for
each zodiacal sign by the Manaeus constructed with a circle tangent
to these outer lines as shown in the previous chapter of Drinkwater.

Now you measure from A and B to the hour line intersections at the
radiating lines from D, not from the horizontal parallel lines within
the circle as implied by the text.

To demonstrate this, look at pages 140-143 of the Dover edition of Albert
Waugh's _Sundials: Their Theory and Construction_.  This is an equivalent
method of constructing the OUTER two lines of solar declination (+/- 23.5
degrees).  He would have had to make a Manaeus to get the intermediate
lines.  Here we could replace A<-->O, D<-->T, and E<-->S between
Drinkwater and Waugh (although E is not shown in Drinkwater's second
figure).  Also, Waugh uses measures from O, not S, (A, not E) but they
should produce the same result when marked off from that point (Hmmm, I'm
not sure that's true--should the distances along the horizontal line from D
been measured from A for the vertical dial??).  Anyway, as you can see,
it is the intersections with the radiating lines at the 23.5 degree angles
that give you the outer lines of declination.

Ron Doerfler

Re: Drinkwater construction help request

[Daniel Roth]

> i'm working through Drinkwater's _Art of Sundial
> Construction_ 

I'm interested in this book. Can you give me the publisher (and ISBN)? 
Thank you.

- Daniel

Drinkwater construction help request

[Jim Lattis]

Greetings All,
i'm working through Drinkwater's _Art of Sundial
Construction_ (which i very much like) but have encountered
a problem that perhaps someone can help me with.  i have
two problems in his section on marking the "Parallels of
Solar Declination" (pp. 44-46).  

First, on p.45 he says "Construct the Maneus as Shewn." 
But when i try to reproduce his equivalent on p.46, i can't
figure out how to fix the distance of the center of the
"zodiacal circle" from point D.  it seems that the hour
line he labels "6" fixes that distance, but that distance
couldn't have come from the diagram on p.44 (as do the
lengths of the other hour lines) because the 6 line is
parallel to the common tangent line and never intersects
it.  what am i missing here?

Second,  (and assuming the first is solved) he instructs us
to "Take the requisite distances, to the individual
"Parallels", along each Hour Line on the second Diagram
from Points 'A' and 'B', and transfer them to the
corresponding Hour Lines on the Dial."   what distance from
'A', for example, is this?   shall i measure along the 8
line, for example, from 'A', extend this line through the
horizontal from 'D', and take the distance where the 8 line
intersects, say, the line for Taurus?  this makes a certain
amount of sense to me, but then how shall i complete the
lines on the winter side of the equinoctial line on the
dial face (e.g. where does 8 intersect Aquarius) for a
simple horizontal dial?  (as opposed to his more complex
example of a diptych dial.)

thanks for any insights.  -jim lattis
-- 
Jim Lattis [EMAIL PROTECTED] "What's so amazing that 
Space Astronomy Labvoice: 608-263-0360keeps us stargazing, and 
History of Science Dept. fax: 608-263-0361what do we think we might 
Univ. of Wisconsin-Madisonsee?"  -Kermit t. Frog