Subject:

Re: Calendar reform dead as a practical issue?

Date:

Fri, 13 Feb 1998 01:05:39 -0800

From:

Simon Cassidy <scassidy@earthlink.net>

To:

CALNDR-L@ECUMAIL7.ECU.EDU

Amos quoted and answered the following question:

> > The calendar's wandering weekdays were designed with no consideration

> > at all given to the convenience of future calendar programmers.
(How

> > easy is it for you to determine the weekday of January 1 from any
given

> > year number?)

>

> Actually, it's not very difficult; you can even do it in your head!
See

> "the Doomsday method" [at http://rudy.ca/doomsday.html].

>

> (IMHO, this algorithm is what motivated the originators of the Gregorian

> reform to choose it over the more accurate Persian 33-year cycle).

but Simon notes:

Even if we suppose that "this algorithm" was around in the 1580's (the

contemporary mathematician Conway is credited with its invention) it

would have not made weekday calculations any easier in pope Gregory's

calendar than in a calendar using the (Persian) 33-year cycle. In fact

"it" works a little better in my reconstruction of Dee's (or Dee and

Cecil's) calendar. I quote from the above web-site:

****************************************************************************

Dr. Conway now teaches the Doomsday algorithm, complete with Century

adjustment, using a very simple audiovisual aid -- your hand.
` _____`
` ____/ ___)___
<---- Doomsday Difference`
`
______) <---- Century Day ("We-in-dis-day" for 1900)`
`
_______) <---- number of DOZENS`
` _____ ______)
<---- remainder`
` \______)
<---- number of 4s in that remainder.`

The Doomsday Difference is the difference between the required date
and a

nearby Doomsday, recorded as so many days "on" (i.e. to be added) or
"off"

(subtracted) from that Doomsday.

****************************************************************************

If the Dee-Cecil calendar had been adopted, A 17th. century "Conway"

method

would follow almost the same steps except for the "dozens" part:
`____________________________________________________________________________`
` _____`
` ____/ ___)___
<---- Doomsday Difference`
`
______) <---- Century Day ("We-in-Dee's-day" for 1600)`
`
_______) <---- less number of 33s in century#+year#`
` _____ ______)
<---- plus remainder`
` \______)
<---- plus number of 4s in that remainder.`
`___________________________________________________________________________`

The Doomsday Difference (the difference between the required date and
a

nearby Doomsday) being calculated in exactly the same fashion as Gregorian,

while the HARDEST piece of Conways method (getting other Century Days)

which is given at the above web-site as:

***************************************************************************

` Sun Mon Tue Wed Thu
Fri Sat`
` 1700 1600 1500`
` 2100 2000 1900
1800`
` 2500 2400 2300
2200`

What's the best way to memorize century Doomsdays? I'm not sure.

Here's what I use. Notice that century Doomsdays fall only on

"Sun-Tue-Wed-Fri". I say "Son to wed Friday", thinking of my own

son, and how pleased I would be if he were indeed getting married

(well, maybe not this Friday!). Combine this with Dr. Conway's

"We-in-dis-day" for 1900=Wednesday, and I can reconstruct the chart

mentally. The tricky part is that the years go right to left in

each row. The easy part is that if you can get just the one row

(the one with 1900=Wednesday in it), the other years are the same

Doomsday, plus or minus 400 years.

***************************************************************************

would be somewhat simpler in the Dee-Cecil calendar:

___________________________________________________________________________

`Sun Mon Tue Wed
Thu Fri Sat`
`
1600 1500`
` 1700
1800`
` 1900
2000`
`
2100
2200`
`
2300`
` 2400
2500`

i.e. add (or subtract) four weekdays for each century forward (or

backward)

from We-in-Dee's-day (WEDNESDAY) for the 1600s..

___________________________________________________________________________

I show the above for the Dee-Cecil calendar rather than the original
Dee

version only because the Dee-Cecil version is completely synchronous

with

the Gregorian calendar for the years 1585-1619 and the years 1981-2015.

The original Dee version would be 1 day ahead to get the VE on March
21

rather than March 20 (under the calendrical meridian at ~77 degrees
W.).

Check all this against my MULTIPLEX PERPETUAL SOLAR CALENDARIUM,

available at

http://www.magnet.ch/serendipity/hermetic/cal_stud/cassidy/perp_cal.htm

and (for those unfamiliar with my reconstruction of Dee's full proposal)
see

http://www.magnet.ch/serendipity/hermetic/cal_stud/cassidy/33yr-cal.htm

---

Dee's Y'rs, Simon Cassidy, 1053 47th. St. Emeryville Ca. 94608.

ph.510-547-0684.
email: scassidy@earthlink.net