Chairman's Column & The Briggs Sundial - A Personal Encounter

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Chairman's Column & The Briggs Sundial - A Personal Encounter
Article · December 1994
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William Mccluney
University of Central Florida
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C
0.11PENDIV
W
*
Journal of the (North American Sundial Society
Torume 1(Number 4
December 1994

c
ISSAI
0
74
-
3
1
97
Editor
Frederick W. Sawyer III
8 Sachem Drive, Glastonbury, Ct 06033
71541.1662@compuserve.com
Chairman
Ross McCluney, Florida Solar Energy Center,
300 State Road 401, Cape Canaveral, F132920
3178838@mcimaiLcom
Treasurer
Robert Terwilliger
2398 SW 22nd Avenue, Miami, Fl 33145
71034.3445@compuserve.com
Membership
Allan Pratt
1936 E. Belmont Drive, Tempe, Az 85284.
71333.2756@compuserve.com
.., in their marriage of mathematics, craftsmanship and 'visual aesthetics,
[sundials] exhibit a humanist unity of culture valuable in an
age of fragmentation.
Burner 1989
Contents
Chairman's Column

Ross McCluney
The Briggs Dial - A Personal Encounter

Ross McCluney

4
National Bureau Of Standards Commemorative Sundial

8
Error In A Misplaced Dial

Fred Sawyer

14
Implications Of Moving The Briggs Dial

Robert
Terwilliger

16
Making A Polar Dial

Robert Terwilliger

17
Reducing A Plane To The Horizontal

Fred Sawyer

19
Digital Dials: Old Power, New
Technologies

Allan Pratt

23
Book Reviews

Fred Sawyer

24
Turner, Of Time and Measurement
O'Malley, Keeping Time
Quiz

26

Renewal Call

27
Quebec Info

27

Annual Meeting

28
Voting Results

27

Digital Bonus

28
rt Nit Graphics
of the qran (Briggs Commemorative Sundial appearing in this issue of the
Compendium were created 6/ (Robert gerwiffiger.
(c) 1994 (North American Sundial Society

Chairrnan's Column
Ross McCluiley
SOCIETY STATUS. Here we are with our fourth
magnificent issue of the Compendium and nearing our
first full year of operation as a growing Society. Our
growth was a bit slow to start, but picked up by mid-year
and now I think exceeds almost all our expectations.
Current membership as we go to press with this last
issue of 1994 is 127, and we really haven't started to
publicize ourselves very much yet!
ELECTION.

As you know ("Organization",
Compendium 1-1), we have been operating this year on
an ad hoc basis, with our Planning Committee serving
as a Board of Directors until we can get a set of ByLaws
written and official officers formally elected. By now all
107 members eligible to vote should have received,
marked, and returned their ballots. All comments on
the ByLaws received by the 1 July deadline were
incorporated in the draft included with the ballot. No
additional nominations for officers were received. We
did add a fifth candidate, Harold Brandmaier for
Secretary. Normally the ballot would only have one
slate of candidates on it, according to our draft ByLaws.
However, since the ByLaws are not yet official, I decided
to leave room for write-in candidates for each position.
We appreciate your votes. Election results are
announced elsewhere in this issue of the Compendium. I
wish to express my appreciation to all of you who
returned your ballots and my delight that our ByLaws
have been approved. The approval of the ByLaws and
the election of a slate of officers and a Board of
Directors makes NASS an "official" organization as of 1
January 1995. We hope to respond to your vote of
confidence with vigorous work on your behalf in the
coming year.
[Note added while in press:
Three ballots were returned
by the post office with the outside peel off labels gone,
so we could not determine to whom they had been
addressed. This explains why three of you with member
number #107 or below did not receive ballots. We are
sorry you did not get to vote in this election.]
CHECKS TO "NASS".
We have finally solved our
checking account name problem! We are now able to
receive and deposit checks made out to either NASS
or
(North American Sundial Society.
So keep those
renewals and new memberships coming!
DONATIONS.
I'd like to offer a special thanks to those
of you who have been willing to help us out in our early
months of financial need with monetary contributions.
Following is a list of members who have contributed
funds over and above their membership dues this year:
Compendium — COotume
t
(
Number
4
Ross McCluney

Fred Sawyer
Robert Terwilliger

Tom Shepard
Allan Pratt

Myron Palay
Michael Mickelson

Kenneth Clark
James M. Holland

James E. Burns
Robert L. Kellogg

Lawrence E. Jones
James Cordon

Ray D. Lowry
John E. Williams

J.G.T.M. Taudin-Chabot
Mel Doharty

Philip W. Bur
George L. McDowell

Robert A. Jones
Burton W. Hays

Stephen J. Madden
On behalf of NASS's growing membership, I wish to
warmly think each of these individuals for helping
create NASS as a vital, stable, and thriving
organization!
MEMBERSHIP RENEWAL. We have received
considerable feedback that you our members like what
NASS is doing. You like our newsletter and this is very
gratifying to us. I hope that each and every 1994
member will renew for 1995. Please don't lose the
membership renewal invoice enclosed with this issue of
the Compendium and return it with your check so that
you can continue to receive an uninterrupted flow of
Compendiums. As a special treat for 1995 renewals, you
will receive in return for your renewal our special
publication on sundial terminology, a membership
roster, and another special publication, titled "The
Cyclopaedic Dialist." These may not all be ready to
send out immediately after you renew, but will be sent as
they are completed in 1995.
SPECIAL PUBLICATIONS.
"The Cyclopaedic
Dialist" is a reprint of the dialing article from the 8th
edition of the Encyclopaedia Britannica (1852) -
obtained by George McDowell from the Britannica
archives. According to Fred
Sawyer, who is working on
this project, the article is 30 pages of history, discussion,
equations, and graphic procedures which cover a wide
variety of dials, including reclining, declining, polar,
equatorial, analemmatic, Foster/Lambert, Capuchin, etc.
- an example of the very best in encyclopedic work.
This article will be combined in our special publication
with the dialing article from Rees' Cyclopaedia of 1810-
1824, another comprehensive introduction to dialing.
The publication of annotated editions of these
significant articles should provide NASS members with
an excellent handbook to sundial design and theory.
The member directory is another special publication that
will be made available only to members of NASS. It
will not be sold or distributed in any other way. All
Woventkr 1994

Taal;
2

allow you to construct accurate horizontal or vertical
dial faces without difficulty. If you are interested in
helping, please contact Allan.
names will be included unless a member informs us by
31 December 1994 that he or she does not wish to be
included.
PLEASE RENEW.
So please return your renewal form
with a check made out to NASS or (North
American
Sundial' Society.
An address label is enclosed that you
can use as a return address sticker on the enclosed self-
addressed envelope, provided to assist you in sending in
your renewal check. Another label is already on your
renewal form. Both labels have your own personal
membership number on them. These numbers were
assigned in sequence as each member joined NASS.
ONGOING PROJECTS.
We have a number of
exciting projects underway, and I invite members to
contact the individuals listed below and offer to help on
whichever project interests them. With this additional
assistance we should be able to complete these projects
in a timely manner.
Annual Membership Meeting.
We would like to have a
meeting of our new Society next Spring at the
Smithsonian Institute in Washington DC. Member
David Shayt has already begun making preparations for
conference rooms, a tour of the Smithsonian dial
collection, and visits to significant DC area dials. If you
would like to work on this project, please contact me at
the above address. And in any event, please indicate on
your renewal form if you would expect to be able to
attend such a conference. We need to be able to
estimate the expected attendance before finally
committing to this meeting!
Glossary Project.
The preparation of a sundial glossary
to be published by NASS and provided to every new
member of the Society (and to 1995 renewing members
once it is published). There are so many sundial terms
and descriptions that the novice has a hard time
understanding the jargon. We hope to overcome this
problem through our glossary project and encourage
members to assist in its preparation. I have agreed to
draft the first version for review and comments and
hopefully for approval in time to distribute to renewing
members early next year. If you are willing to review
and comment on this draft, please contact me at Florida
Solar Energy Center, 300 State Road 401, Cape
Canaveral, FL 32920, or via the Internet at address
3178838@mcimail.com
.
Amateur's Guide.
Allan Pratt is beginning work on a
booklet entitled "Amateur's Guide to Building
Sundials", which should be ready in late 1995. In
conjunction with the guide, you will be able to order
templates specifically constructed for your location to
Sundial Slide Show.
The idea is to put together a
general interest slide presentation on sundials suitable
for a general audience and easily tailored to children in
grades about 6 and above. This would be made
available on loan to members for presentations in their
local communities. It could also be the beginning of a
small lending library of such educational materials.
This is currently only an idea in search of a leader.
Several of us have slides we could loan out for
duplication and inclusion in one or more of the slide
shows.
NASS's Great American Sundial Hunt.
All members
can participate in this active NASS project. Get a
registration packet from dial Registrar Allan Pratt at
1936 E. Belmont Dr., Tempe, AZ 85284, Compuserve:
71161,2367 , and go out and document sundials in your
area.
Increasing Membership.
This is another project all
members can participate in. Get copies of our
membership application form from Allan - or use the
extra one included in this packet - and send them out to
friends, colleagues, and acquaintances you think might
be interested in sundials and dialing.
NASS Commissioned Sundial.
The commissioned dial is
Fred Sawyer's suggestion. The idea is to commission a
small dial design that can be offered via subscription to
members of NASS. We could do a limited edition,
complete with a NASS-significant inscription or logo.
If we get a good deal of interest, we could consider an
annual commission - to provide members with an
opportunity to find interesting new dials, to encourage
designers, to generally increase the dial population
around the country, and to stimulate interest in
collecting. The designs we look at could be quality
reproductions of historic dials, or universal dials, or
custom-built dials for subscribers' specific locations. In
any event we want them to be dials that work. If you are
interested in this idea, please contact Fred Sawyer for
more information and ideas.
Articles for the
Compendium. Now that we have a large
and growing membership, the percentage of articles for
the Compendium from NASS officers should decrease,
but this can only happen if we receive articles from you
our members. If you have designed and built, or had a
part in the design and construction of an interesting
sundial, please consider preparing a short article, ideally
with drawings and/or photographs, about your dial for
Compendium COorume 1 dumber 4

November 1994

e3

the
Compendium.
You might have another idea for an
article suitable for publication in the Compendium. Send
your articles to Fred Sawyer. If you don't think you are
much of a writer, never fear, Fred is here, here to help
you with your article if you wish. Perhaps you know
something about a sundial of historic significance. If so,
consider writing an article about it for us. Maybe you
know someone other than yourself who is an active
dialist. Consider writing an article about this person
and his or her sundials. If a full article is not your cup of
tea, why not just send in a short letter to the editor?
We'd like to publish a sample of letters from our
members in future issues of the
Compendium.
Sundial Design Software Project.
Sundial design
software from a couple of authors is available to us for
evaluation and possible distribution as a NASS special
publication. What we need is someone to evaluate the
software and possibly improve the user-friendliness
and/or other features of it before we release it as a NASS
product. Please contact me if you are interested in this
project.
Nonprofit Status. We
are looking for someone to obtain
and fill out the forms needed to register as a not- for-
profit organization with the U.S. Internal Revenue
Service. Once we receive this designation, we will be
able to accept tax-deductible donations. When our
membership is large enough we will also be eligible for
bulk mail postal rates. Currently we have to pay full
first class postage to ensure timely distribution of our
newsletter.
That completes my list for now. I think you can see that
NASS is active, growing, and creative. I hope that you
will like our current directions enough to renew your
membership for next year. I look forward to a
rewarding and active Society in 1995.
The Briggs Dial - A Personal Encounter
Ross McCluney
At the top of my list of favorite sundials is the Lyman
Briggs commemorative sundial erected in 1948 at the
National Bureau of Standards in Washington DC, a
color photograph of which can be found opposite page
101 of "Sundials, How to Know, Use, and Make Them,"
by R. Newton Mayall (the designer of the Briggs dial)
and Margaret W. Mayall, Sky Publishing Corp.,
Cambridge, MA, 1938, 1973 (reviewed in the last issue
of the
Compendium).
A black and white photograph can
be found on p. 133 of "A Choice of Sundials" by
Winthrop W. Dolan, The Stephen Greene Press,
Brattleboro VT, 1975. (The "Bureau" as it used to be
called, was renamed the National Institute of Standards
and Technology, or NIST, a few years ago.)
The main reason I like the Briggs dial so much is that it
combines the best of several dialing worlds in one
sundial. It actually has two sundials on it, a solar (or
apparent) time sundial and a local standard time sundial
(split into two parts). All are located on the same
inclined dial plate, with the two standard time dial parts
above and below the centrally located solar time one.
Behind the dial plate is a curved noon mark surface that
receives sunbeams transmitted through a pinhole in the
center of a "sunburst" pattern at the top of the dial plate.
At solar noon, the location of the sun spot on this curved
surface can be used to tell the date and the conversion
between solar time and local standard time for that date.
The curved surface contains an analemma, a plot of the
equation of time versus the sun's declination for each
day of the year.
A beautiful rendition of the Briggs dial plate was drawn
by Bob Terwilliger for this issue of the Compendium and
is reproduced in Graphic [1]. His drawing of the
markings on the curved noon mark surface is shown in
Graphic [2].
Because the hour lines of a standard time dial usually
have the shape of the analemma, it
can be confusing to
tell time using them. The characteristic distorted figure
8 shape of the analemma, shown in Graphic [2], makes
it difficult to tell which part of it to use in telling the
time. To aid the observer, these dials must have the
dates marked around various places on each analemma,
and there must be a separate complete analemma for
each time mark, whether they are hourly, half-hourly, or
every 15 minutes marks.
Mayall got around the problem of the ambiguity of
reading time with figure of eight time marks by splitting
each analemma into two, the upper right and lower left
portions of the analemma in his top standard time dial
half (for the winter/spring half of the year) and the other
half for the bottom one (for the summer/fall half of the
year). The top sundial half reads local standard time
correctly from 22 December to 21 June and the bottom
one reads time for the other half of the year, 22 June
through 21 December.
Compendium q)oiume

i (Number 4

November 1994

Page 4

OF STANDARDS
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While attending a conference last Spring at NIST's
sprawling campus near Gaithersburg, Maryland, I came
across the Briggs dial in the courtyard of the main
administration building. I was thrilled at last to see this
dial "in person" and realized that the sundial had been
moved from its original location on the old "Bureau
Why is there no 4:15 line on the (Briggs dial?
The solution (offered by Robert Terwilliger) to the
mystery of the Briggs 4:15 line lies in the 2+ degree
longitude correction. Noon is not at the center of the
dial. At a given temporal distance from the dial center,
the hour lines to the west are further apart than the
corresponding lines to the east, and the effect is
exaggerated as you approach the extremes. Mayall had
room to add 15 min. lines outside of 8 am and 4 pm,
but when he did it, he got a crunch in the afternoon.
By eliminating the 4:15 line, the space outside 4 almost
matches the space inside 8, and there are exactly 3
more full lines in each direction.
grounds" in Washington DC to the new location,
probably without making any changes in the positions of
the gnomons or the markings on the dial plate. It didn't
look as if anything had been changed. I wondered if the
people who moved the dial had adjusted it for the new
location or if the errors induced by the move were small
enough to be insignificant.
The NIST library is just a short walk from the courtyard
where the sundial is located. A quick check with
Reference Librarian Marietta Nelson produced a copy of
the brochure titled "Commemorative Sundial" that
appears to have been printed shortly after the completion
of this sundial, which was erected in August, 1948 "on
the main road into the Bureau grounds." The text of
this brochure and some of its figures are reproduced as
our next article.
One thing that interested me was the question of how
large the errors are in this sundial resulting from its
move from near
the corner of Connecticut and Van Ness
in Washington to its current position
near Gaithersburg.
Compendium

oiume umber 4

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
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5

A phone call to NISTs historian, Karma Beal, yielded
the information that the sundial was moved in April of
1966 and the new Gaithersburg site of the National
Bureau of Standards was dedicated in November of that
year. She later sent me a lot of additional information
and the photographs reproduced here.
The dial itself gives its original latitude as 38d 56m 32s
N but I could find no mention of the longitude on the
sundial during my visit. I did see what looked like it
might be the longitude of the site on the noon mark
behind the dial plate, but at the time I wasn't sure if this
was the longitude. After examining the map showing
the Washington location it became clear that the
numbers given do refer to the longitude of the
Washington site: 77d 03m 59s W.
Longitude is critical to the proper operation of any
standard time sundial. Since the earth rotates at the rate
of 15 degrees per hour, a 1 degree error in longitude
would produce an error in a sundial's time reading of
about 1/15 of an hour, or 4 minutes.
Among the materials later provided me by Ms. Beal was
a copy of a letter from sundial designer Mayall to Mr. L.
E. Barbrow, Chief of the Photometry and Calorimetry
Section of NBS dated 10 January 1965 giving the
coordinates of the new site and his estimate of the error
created by moving the sundial to a new latitude and
longitude without any change in its tilt from horizontal
or rotation from true north. Mayall provides the latitude
of what he calls the "zenith telescope" at the
Gaithersburg site as 39d 08m 13s N and the longitude as
5h 08m 48s, which converts to 77d 12m 00s W. These
coordinates and their differences are summarized as
follows:
Washington
Gaithersburg
Differences
32s
Latitude
38d 56m 32s N
39d 08m 13s N
00d Ilm 41s
Longitude
77d 03m 59s W
77d 12m 00s W
00d 08m Ols W or
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Thus the change in
longitude was approximately 08m
0 ls or 0.13361d in angle, corresponding to 32 seconds
of time on the standard time sundials. The 32 sec. error
matches the one predicted by Mayall in his letter. This
error is probably too small to be of much significance,
since most sundials can be read correctly only to about 1
or 2 minutes of time anyway.
To be more strictly correct, one should consider the
effects of changes in both the latitude and longitude on
the dial. The longitude move should have no effect on
the solar time sundial, if it was realigned properly, but
both latitude and longitude changes can affect the
standard time dial and the latitude effect can have an
impact on the solar time dial's readings.
Mayall was of course aware of this and detailed in the
letter to Barbrow his calculations of the resulting errors
if no change was made in the sundial or its installation
at the new site, i.e. if it was accurately oriented toward
true north and the dial face was made to have the same
inclination from the horizontal as it had at the
Washington site.
Compendium
—
Cootunte t cumber 4

(November
1994

`a8¢
6

Here is what Maya11 said in his letter:
"The longest distance on the dial is that from the hole in
the sunburst to the Analemma—which is 1 foot; therefore
the longitude difference is 0.002 feet. The ray of light
will actually be out 0.002 feet in the new location. This
is negligible except for a purist. The dial should be
raised at an angle of 0.003 feet in 1 foot to correct for
latitude. Again a negligible amount, except for the
purist."
"There is nothing much you can do about the standard
time elements, but you could toy with adjusting the dial
for latitude. However, unless you are desirous of
having the dial as near as possible to being correct, I
don't think I would bother. Maybe you will have an
earth tremor that will throw it out a thousandth of a foot
one way or the other.
At the end of his letter, Mayall provided a sketch
indicating a tilt upward of the front (south edge) of the
dial by 11 m 41s to compensate for the latitude change.
As pointed out by Bob Terwilliger, however, the tilt
should be the other way - the front (south) edge of the
dial should tilt downward by 11 m 41s not upward,
thereby increasing the elevation from the horizontal to
account for the more northern location.
As a result of this letter Barbrow wrote an internal
memo dated 12 January 1966, apparently to the Director
of NBS, in which he said: "You will note that he
confirms our previous conclusion that the Sun Dial can
be moved to Gaithersburg without introducing any error
large enough to be concerned about." The new NIST
campus of the NBS was dedicated in November of 1966
and as mentioned previously the dial was moved in
April of that year.
The results shown above lead me to conclude that all is
well with the Briggs sundial. The residual errors
resulting from the move are indeed quite small and not
noticeable, except as Mayall says, "for the purist." The
NASS organizing committee has taken on a project to
further document this important American sundial and
to enter it into NASS's growing database of North
American sundials, under the able leadership of sundial
Registrar Allan Pratt. This work has raised several
interesting questions about the accuracies of sundials. I
plan to discuss sundial time measurement errors more
generally in a future article in the Compendium.
This project has captured the interest of all the officers
of NASS. It really is a lot of fun to discover and
document historically interesting dials in America. I'm
thankful for all the able assistance provided by NASS
members Terwilliger, Sawyer, Pratt, and Robert
Braunberg of Rockville, MD, who made measurements
and rubbings of the dial which were very useful in
producing the drawings used with this article. From this
experience I can heartily recommend that all members
join us in NASS's Great American Sundial Hunt.
Inscriptions found on the Briggs sundial
On the west side of the horizontal base plate: "Erected
in 1948 by the Members of the Staff of the National
Bureau of Standards
On the east side of the horizontal base plate: "In Honor
of Lyman James Briggs Third Director who retired Nov.
5, 1945."
The latitude is inscribed behind the dial plate on the
curved analemma surface. The longitude is inscribed
along the noon mark on this surface.
Front rim: T. Newton Mayall, Des. Colonial Brass
Co., Fabr. Frederick Bagshaw, Engr."
Sides: "Lyman Briggs Director 1933-1945 Samuel
Wesley Stratton Director 1901-1922 George Kimball
Burgess Director 1923-1932"
The civil time dials have short (about 2.5 to 3 inch)
gnomons rising from the dial plate to a short flat thin
line gnomon pointing to the north celestial pole, parallel
to the earth's axis, as is the dial plate. The solar time
gnomon is placed on a curvey X support that is supposed
to symbolize the shape of an hour glass. On the top is a
rectangular solid bar aligned toward the north star and
tapering to a point at the north end.
The gnomons are held to the dial plate by flat-head
screws inserted from beneath the plate, screwed into
tapped holes in the gnomons.
Compendium
—
Coolume
1 %umber 4

(November 1994

page 7

National Bureau of Standards Commemorative Sundial
National Bureau of Standards Welfare Association
[Editor's Note: This article reproduces the booklet published at the time of the dedication of the commemorative sundial
at the U.S. National Bureau of Standards in 1948. A copy of the booklet and the photos reproduced here were kindly
provided to us by Karma Beal, Archivist in the Office of Information Services at the National Institute of Standards and
Technology, the successor organization to the National Bureau of Standards.]
National Bureau of Standards
Commemorative Sundial
Erected August, 1949
Dr. Lyman James Briggs retired in 1945, after having
served as Director of the National Bureau of Standards
since 1933. A desire to mark the occasion arose in the
hearts and minds of his colleagues, whose love and
esteem he had so completely won. We immediately
discussed the matter with Dr. Briggs, who expressed the
request that no ceremony of any kind be held in
connection with his retirement. We learned, however,
that Dr. Briggs had for some time cherished the idea
that a sundial be erected on the grounds of the Bureau as
a memorial to its first two Directors, Dr. Samuel Wesley
Stratton and Dr. George Kimball Burgess. This gave us
the needed clue, and we decided to erect a sundial in
honor of Dr. Briggs on the terrace east of the Chemistry
building. Furthermore, this sundial would
commemorate the services to the National Bureau of
Standards of its first three Directors - Doctors Stratton,
Burgess, and Briggs.
Plans were developed to obtain a sundial of unusual
design and of as high a degree of accuracy as could be
obtained without the use of adjustments. An authority
on sundials was engaged to design and supervise the
construction. After numerous delays, due to postwar
conditions, the sundial was set in place on August 13,
1948.
The sundial was very favorably located on the main road
into the Bureau grounds. Each day it reminds those who
had the pleasure of working with Dr. Briggs of his
exemplary character and of the high esteem in which he
is held. In addition, it will perpetuate the remembrance
of the contributions that our first three Directors made
toward bringing the National Bureau of Standards into
world fame. A detailed description, by the designer, of
the commemorative sundial and of its use is given on
the following pages.
Commemorative Sundial and Its Use
Our sundial is composed of three principal parts: 1. the
base, 2. the dial plate, and 3. the analemma.
Base
The bronze ring around the pedestal commemorates the
Bureau's three former directors. The base plate bears an
inscription to Dr. Briggs, as follows:
"Erected in 1948
by the members of the staff of the National Bureau of
Standards in honor of their third Director, Lyman
James Briggs, who retired on November 5, 1945."
Dial Plate
The hour lines for telling time are inscribed on the dial
plate, which reclines from the observer. Three sets of
hour lines are used. Each has its own gnomon to cast a
shadow, which is used to indicate the time.
The upper and lower gnomons point out Eastern
Standard Time every day throughout the year. The
middle gnomon resembles an hour glass with a bar
across the top, it indicates local apparent time (sun time)
throughout the year.
Two sets of hour lines are used to show standard time in
order to avoid confusion in reading the time. If the
position of the shadow of the upper edge of the
pyramidal gnomons is plotted for each hour standard
time throughout the year, a series of overlapping figure
eights will result; to avoid this overlapping on our dial
plate, that portion of the figure eight representing the
period from December 22 to June 21 is separated from
that portion representing the period from June 21 to
December 22. This produces two sets of deformed hour
Compendium q)otume
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lines that do not overlap and makes it possible to read
standard time directly and easily.
The deformation in the hour lines occurs because a
correction has been applied to the hour lines as they
appear in the middle or apparent time dial. This
correction is the sum of two factors - one variable, the
other static.
The first factor is applied to change the local apparent
time hours to local mean time hours. This factor is
variable and represents the equation of time, which is
the difference between mean time and apparent time. It
is this application of the equation of time that produces
the deformed lines, or figure eights.
The second factor is the difference in longitude,
expressed in time, between the sundial's position and the
standard time meridian, which in this case is the 75th.
This factor is static and remains the same throughout
the year; therefore it is applied to adjust the figure eights
or deformed lines of local mean time to positions where
they become Standard Time hour lines. This adjustment
takes place in a lateral direction east or west of their
normal position on the dial plate, as the sundial is
located east or west of the Standard Time meridian. In
this manner the lines are brought into the proper
position to indicate standard time without the use of
tables or mental arithmetic.
Analemma
At the top center of the dial plate there is a sculptured
sun, in the center of which there is a very small hole.
This hole lies in the plane of the true meridian and is
used to allow the rays of the sun to pass through to the
arc in back of the dial plate. The spot of light thus
formed points out noon Eastern Standard Time and
noon local apparent time. On this arc may be seen the
full figure eight, or analemma. If this were a local mean
time analemma it would cut the meridian line four times
and would appear symmetrical with respect to the
meridian line.
The correction for longitude difference causes this
analemma to be moved bodily to the west or left of the
meridian as explained above. The standard time hour
lines on the dial plate are just a smaller edition of this
full analemma.
Also inscribed on this arc are several facts concerning
the position of the sun and calendar references, which
are indicated by the spot of light.
Use of the Sundial
An instrument of this kind, which has been constructed
carefully, is much more than a time-telling device. It
can be used to demonstrate certain well-known and
accepted facts about the sun and it can be used to make
clear other facts that are not always quite obvious. For
example:
1.
The irregular apparent motion of the sun can be
observed by watching the position of the shadows of the
gnomons change from day to day with respect to the
hour lines. This irregular apparent motion of the sun is
very clearly shown by the analemma.
2.
Whether the sun is "slow" or "fast" can be determined
easily by comparing the time indicated on the various
dials on the dial plate.
3.
The difference between apparent and Standard Time
can be obtained.
4.
When the shadow of the gnomons reaches the central
horizontal line on the standard time dials, the sun is on
the celestial equator.
5.
When the shadows travel along the upper curved lines
of the standard time dials, the sun has reached its
greatest southern declination and winter begins; likewise
when the shadows reach the lower curved lines, the sun
has reached its greatest northern declination, and
summer begins.
6.
The upper and lower horizontal lines at the left and
right of each standard time dial indicate the time of
sunrise and sunset.
7.
The day of the year can be determined when the spot
of light is on the analemma.
8.
When the spot of light appears on the meridian line,
the sun has reached its greatest height above the horizon
on that day. The meridian height or altitude of the sun
can be obtained in degrees from the right hand column
or scale.
9.
When the spot of light is on the meridian line, it
signifies that the sun lies in the plane of the true
meridian at that moment, and the sun is due south.
10.
The sun's declination (number of degrees north or
south of the celestial equator) can be obtained from the
left column or scale when the spot of light is on the
meridian line.
.....Compendium Qlottinte t (I umber 4

Aovember
1994

12

11.
The horizontal lines cutting the analemma, in
addition to indicating the day of the year, serve to show
which side of the analemma should be used for the spot
of light to indicate noon Eastern Standard Time.
12.
Another purpose of including the analemma is to
provide a larger and more accurate hour line by means
of which an observer can set his watch correctly at noon.
13.
The analemma disproves the usual belief that the
sun agrees with the clock four times a year. Note that
the analemma cuts the meridian only twice at
Washington. Only when the sundial is on or very close
to a standard time meridian will it agree with the clock
four times a year. In some localities, Boston for
example, the apparent time sundial never agrees with
the clock.
General Facts
The plane of the dial plate lies parallel to the earth's
axis; therefore its surface, if extended infinitely, would
cut the celestial pole (not the north star).
Because of the position of the dial plate, the sundial is
technically referred to as a Polar Sundial.
The bar across the top of the hour glass gnomon points
to the celestial pole.
The apparent-time Polar Sundial is one of the easiest
and simplest to construct, yet very few have been made.
There are three ways of telling time by the sun - 1. by
shade, 2. by light, and 3. by a magnetic needle. Our dial
makes use of two of these methods - shade and light.
The hours on the dial plate are indicated by a shadow,
and the time and other data on the analemma are
indicated by a spot of light. The combination of light
and shade indicators on the same dial is not often seen,
but it adds interest to the instrument.
There are three methods of telling time by the sun:
a.
By measuring the hour angle of the sun from the
meridian.
b.
By measuring the sun's altitude.
c.
By measuring the sun's azimuth.
ordinary garden variety of horizontal sundial with its
sloping gnomon.
Sundials can be made to serve a particular place or
places, to serve anywhere (universal), or to serve some
specific purpose such as a noon mark. Our dial is made
for one place - the latitude and longitude of the Bureau's
grounds. It cannot be set up in New York, Philadelphia,
Chicago, or any other place off its meridian and be made
to tell the correct time of the locality. Also, insofar as
the analemma is concerned it is made for a specific
purpose - to show Apparent Time and noon Eastern
Standard Time.
The arrangement of words, numerals and other data has
been designed to be self-explanatory so that an observer
will not require a book of instructions.
Color
-
Scheme
All incised-lines, numerals and figures have been filled
with color to make the instrument more interesting and
easier to read.
On both the analemma and the dial plate all lines
referring to Standard Time have been filled with bright
red; all references to apparent time are shown in white;
and all references to the calendar are indicated in blue.
Because apparent
time
is almost always given in the 24-
hour system, the apparent time lines on the dial are
indicated that way, in Arabic figures; therefore, 3:00
P.M. apparent time is shown as 1500.
Standard Time is the time shown by watches and clocks
and their dial faces usually display 12 hours; therefore,
the Standard Time hours on our dial are marked in the
same system in Roman numerals.
Acknowledgments
We
are especially indebted to Mr. R. Newton Mayall,
who designed and supervised the construction of our
sundial. The Colonial Brass Company fabricated the
parts, Mr Frederick Bagshaw did the engraving. The
pedestal for the sundial was made by the Earley Studio.
The bronze ring around the top of the pedestal was cast
in our Bureau foundry.
National Bureau of Standards
Welfare Association
Our dial makes use of the most common method - that
of measuring the hour angle of the sun, just as does the
at
qk
oveletbet. 1994
e 13
Tao

Error In A Misplaced Dial
Fred Sawyer
The fact that moving the Briggs dial to a new location
resulted in no appreciable error in the dial's readings is
comforting. Indeed, it probably could have been
removed considerably farther north without causing
much trouble. But this discussion has raised an issue of
broader concern; in fact, it is one which should concern
anyone not living at latitude 40 degrees but wishing to
buy a garden variety horizontal dial in the U.S or
Canada.
Most such dials are designed to function well, reading
local apparent time, at the 40th parallel. These dials
will continue to work well at other latitudes if they are
inclined out of the horizontal plane so that their
gnomons remain parallel to the celestial axis. However,
given that most people will ignore the inclination and
continue to treat the dial as a horizontal, regardless of
the latitude, errors occur. How big are they? How do
they vary with season and time of day? The following
mathematical development is intended to provide
formulas to answer these questions.
We begin by recalling three formulas, familiar in basic
astronomy and derived earlier in
"Solving The Spherical
Triangle" (Compendium,
1-3, August 1994):
sin
A=
sin
L
sin
D +
cosL cosD cos
T (1)
cos A
sin
Z =
sin TcosD

(2)
cot Z
sin
T =
cos Tsin
L —
tan D
cosL
(3)
where
L =
latitude,
A =
solar altitude,
D =
solar
declination,
T =
solar hour angle, and
Z =
solar azimuth
(as measured from south).
Another equation we will need results from multiplying
both sides of equation (3) by the corresponding sides of
equation (2):
cos A cosZ = cosT
sin
L
cosD — sin
D
cosL (4)
With a properly identified spherical triangle, this
equation is simply an example of the second to last
equation listed in our prior article.
Suppose now that we are given a traditional horizontal
dial designed for latitude
L
2
but set up as a horizontal at
latitude
L .
Select a point
P
at a unit height on the
shadow casting stile of the dial's gnomon, and drop a
perpendicular line from this point down to point
G
on
the dial face. Point G will lie on the meridian (noon)
line
NGC.
At any given date and time, the shadow of point
P
on
the dial face will be point
S,
determined by the angle
NGS
equal to
Z
the solar azimuth, and length
GS equal
to
cot A
(both by definitions of azimuth and altitude).
The shadow of the entire stile will fall on line
CS,
where
C
is located so that length
GC = cotL
2
(i.e.
C
is the
center of the dial - or possibly a point at infinity if
L
2
=
0).
We know from the traditional dial construction that
tan
NCS =
tan T
2
sin
L
2

(
5
)
where T
2
is the reading given by the dial (but not
necessarily equal to the current time 7).
We also know that if
N
is chosen so that
NS
is
perpendicular to
NC,
tanNCS = NS I (NG + GC)
= cot
A
sin Z
/ (cotA cosZ + cotL
2
)
(6)
Combining equation (5) and (6) yields equation
(7):
tan
T2 =
cos
A
sin
Z
/ (cos
A
cos Zsin L
2
+ sin
A
cosL
2
Substituting equations (1), (3) and (4) into (7), and
dividing the numerator and denominator by
cos D
yields:
tan T
2
= sin
T I
(cos Tsin
L
sin
L
2
-
tanD cosL sin L
2
+sin
L
tan
D cosL
2
+
cosL cos
T cosL
2
)
To simplify the denominator, we note that for any two
angles
L
and
L
2
,
sin
(L — L
2
) = sin
L cos L
2
—
cosL sin
L
2
cos(L —
L
2
) =
cosL cosL
2
+ sin
L
sin
L
2
So, if we set
M =
L —
L
2
,
then :
tan
T2 =
sin
T 1
(cos Tcos
M
+ tan
D
sin
M)
(8)
omp

Ofiltrit 1
(Number
4

Aoyenther 1994

This is the equation we have been seeking.

It
demonstrates that at time
T
the dial's reading T
2
depends on the solar declination and on the difference
between its actual and intended latitudes. Note that it is
only the difference
M
between the latitudes, not the
specific values of the latitudes themselves, that comes
into play.
From the perspective of spherical trigonometry, this
same result can be obtained by noting that our problem
requires solving the triangle with vertices at the north
pole, the sun's position, and a point on the meridian M
degrees from the pole.
Of course, the equation, however derived, can be used to
determine the exact error in the dial's reading for any
given date (or solar declination)
D,
time
T,
and
displacement
M
(where
M
=
L
—
L
2
). An analysis of
the way this equation works shows that the error can be
zero at most four times in any day.
At
noon
and
midnight there is never any error. The other two
possible times of zero-error are the morning and
afternoon hours (if any) for which
cosT =
tan
D
cot(M/ 2),
abs(D) < abs(M 1
2)
[Substituting
tan
D cot(M 1
2) for
cosT
in equation
(8) will yield the result that T
2
=
T
.]
Note that this error analysis actually is valid for any
non-declining gnomonic sundial; it need not be limited
to horizontal dials. The restriction to non-declining
dials is necessary (at least for this particular solution to
the problem) because the development of the equation
uses the fact that the meridian line
NGC
coincides with
the perpendicular projection of the gnomon's stile onto
the dial face; this condition is not valid for declining
dials.
We can extend the equation to the non-horizontal case
because a dial at latitude
L
2
with inclination I (and no
declination) is equivalent to a horizontal dial at latitude
L
2
-
I
;
and displacing the inclined dial to latitude
L
amounts to displacing that horizontal equivalent dial to
a horizontal position at latitude
L
—
I.
We know
equation (8) works for the horizontal dial case where
M =
(L
— /)— (L
2
— /) =
L
—
L
2
.
But this shows
that it will also work if we deal directly with the inclined
dial and latitudes L
and L
2
;
the inclination cancels out
of the equation and plays no role. We can extend the
treatment to non-horizontal dials precisely because the
equation depends on the difference between latitudes
and not on the values of the latitudes themselves.
Thus, we come full circle to the polar (inclining, non-
declining) Briggs dial. The graphic displays the error
that would have resulted in the Briggs dial readings if
the dial had been moved 5 degrees to the north - about
345 miles (so
M =
5). The following table provides
values of the dial reading to within the nearest minute.
[The appearance that there is no error in the reading at
any time of day when the declination is zero is a result
of rounding to the nearest minute.] With a
displacement of 5 degrees, the error in the dial's reading
during most of the day is within 10 minutes, but it is
clearly not constant throughout the day. For most days
(i.e. when
abs(D) > 2.5),
it begins at one extreme in the
morning, reduces to zero by noon, and then grows to the
opposite extreme through the afternoon. For those days
close to the equinox (i.e. when
-2.5 < D < 2.5),
the error
is very small and actually disappears once in the
morning and again once in the afternoon.
Compendium

utnel (*Oct 4..

ember 1994

page 15

7
5
M = 5
ti
Gnomon
Graphic by Robert Terwilliger
Time
Sundial
Time Readings
D = -23;24 D = 0
D = 23:24
4 am
3:53
4:00 4:08
6 am
5:51
6:00 6:09
8 am
7:52
8:00 8:07
10 am
9:55
10:00
10:04
12 pm
12:00
12:00
12:00
2 pm
2:05
2:00
1:56
4 pm
4:08 4:00
3:53
6 pm
6:09
6:00
5:51
Implications Of Moving The Briggs Dial
Robert Terwilliger
The Lyman Briggs dial consists of two separate dials. A
standard time dial divided into two parts, and an
apparent time dial. The standard time dial includes two
sets of half-analemmas to compensate for the equation
of time. For this discussion we can ignore them. If the
straight hour lines they replace are correct, they will be
correct.
There are two ways to adjust a standard time sundial to
its position in a time zone. The hour lines can be
calculated and drawn to include the adjustment; or the
hour lines can be laid off for local time and the
adjustment applied by rotating the entire dial about the
polar axis, toward the central meridian, the same
angular distance it is offset from the meridian. Maya11
calculated the adjustment into the hour lines, leaving the
plate horizontal.
The Briggs dial was moved only .195 degrees north and
.133 degrees west, which all agree is negligible. This
discussion assumes a more substantial move. The dial
face of the Briggs model included with this issue is an
exact recreation. If you assemble and mount it, you will
have the experience of making a more substantial move
- right into your own
back yard.
The two dials which make up the Briggs dial are
referenced to two different longitudes. The standard
time dial is calculated for the the central meridian, 2.07
degrees east, the apparent time dial to the local
meridian. The only way they will keep time together, as
intended, is if the dial is mounted with the north-south
angle of the plate set to the latitude, and the entire dial
positioned at the same longitudinal distance, in the same
direction, from any central meridian.
If the new location does not fit these criteria, the options
are limited. Only one dial can tell time accurately, and
the obvious choice is the standard time dial. After
aligning the dial center with the new meridian, and
adjusting the angle of the plate to the latitude, there is
no longer the luxury of choice as to how to adjust for the
new position in the time zone.
The hour lines have already been drawn. The dial plate
must be rotated about the polar axis, toward the central
Compendium Tofunte t
Number 4

(November
1994

pa8e 16

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