This department
only deals with portable sundials equipped
with a compass. We describe in Part 1 the different types developed
between
the 17th
and the 19th century.
You will find technical background information in the 2nd
Part. Concerning the non-magnetic
military
sun compasses
we recommend the excellent essay
by Malcolm Barnfield
The
Sundial Goes to War on the
website
Sundials.
Pic. at left: Hunter-type sundial compass
(manufacturer:
Houlliot,
c.1930).
Technical Data: Dia.:
2" / 50 mm;
Depth (clsd.): 20 mm; Height
(scales erected) : 2" / 50 mm.
(Click
on the picture for
enlarged view -
see further down other Houlliot-made models)
See other
examples in the online collections of the
Museum of the
History of Science and of the
National Maritime Museum.
CONTENT
Part 1 - Collection
-
EUROPEAN
DIPTYCH sundials (XVIIth C.)
-
Modern
sundials (XXth C.): U.S.A.:
ANSONIA
SUNWATCH and
BOYD SUN-TIME;
Austria: maker
W.A.
-
CHINESE
sundials
-
CRESCENT sundials
-
EQUINOCTIAL compasses
(Augsburg type)
-
BION,
Nicolas
-
BUTTERFIELD,
Michael
-
MAGNETIC
DIALS (PANTOCHRONOMETERS)
-
GNOMON
Compasses
-
L'ABEE-LUND'S
WATCH COMPASS
Part
2 - Technical Information
(incl.
User
Directions) and Bibliography
IVORY SUNDIALS / FRANCE
These two-fold ivory sundials are called
Dieppe-style
because they were originally developed and mass produced by Charles
BLOUD in the northern French city of DIEPPE (Normandy) from 1666 on.
His brothers (or sons?) Gabriel and Jacques continued the trade and
were first imitated by Ephraïm Sénécal,
then by Jacques Sénécal (see table 2, center
photograph.
Picture at left: ivory instrument, typical of Ch.
Bloud's workshop although unsigned - France, 17thC.
Picture at right: User's instructions (dated 1653) incl.
computing of the time by night (moon clock) and the high tide (
facsimile
available).
Table 1 - Detail views of the four sides
Table 2 - Various examples.
Tab.
1
|
COMPASS
Background: list of
cities
(Pictures
courtesy James Frellsen / Fleaglass)
|
CALENDAR
(...)
|
SUNDIAL
Note: pin
gnomon is missing
|
LUNAR
VOLVELLE
(night clock)
|
Some items feature many functions: Italian and Babylonian hours (see
Definitions above), seasons curves and a latitudes table.
They have on top of the lid a universal dial and a polar dial. We find
inside these sundials a vertical and a horizontal dial. Under the
compass is also an analemmatical dial. This device is governed by a
rotating disk with a perpetual calendar.
Tab.
2
Instrument
with
pendulum
(not signed)
Probably France, late 17th C.
Picture
Jaypee (priv.
coll.).
|
DIEPPE style sundial,
late 17th C. built by Sénécal |
LIENHART MILLER
(Pic. at l.: Augsburg, Maximilian Museum, at r.: Vivielle's
catalogue)
B/w
pictures courtesy Cdt
Vivielle's
priv. coll. |
PORTUGUESE SUNDIAL
Wood, ink, paint (19th C.), signed
I.S.
i.e.
Iohannes (Latin for
Joao)
da Silva.
The daylight hours are indicated for Portugal's mean latitude (38-39
deg.)
 |
The words printed on the rear back face read 'VERDADEIRO AUTOR JOAO DA
SILVA'
(Maker: Joao da Silva).
Note:
This exhibit doesn't
belong to the Online Compass Museum. These pictures were sent by a
friendly visitor (priv. coll.). |
North
is
indicated with a fleur-de-lis
but also EAST with two tiny symbols.
(go to MISCELLANEOUS / Cardinal points)
(Click
on the picture for a
detailed view of the compass).
Technical
data
- Dimensions: 68 x 48 x 14 mm
- Weight: 33 gr
- Pendulum: lead bead
|
SPANISH SUNDIAL
(Replica: go to
Villa Alcor)
CZECH SUNDIAL
Unsigned XVIIIth C. sundial with cardinals in Czech language*
|
|
s
Pictures courtesy Steinbrich-Fricke
(Click
on images for enlarged views)
* S. Miscellaneous /
Cardinals
|
Technical
Data
- Dimensions: ... mm
- Pendulum: Lead
- Material: wood, ink,
- Date: 1748
|
BRITISH SUNDIALS
GERMAN
SUNDIALS
The two most important manufacturing cities in Germany
were Augsburg (s.
Equinoxial
systems further below) and
Nuremberg. In this city, sundial makers first
produced diptychs
made of ivory like in France (Dieppe) and later simple one made of
paper and wood.
A well-known manufacturer was Ernst Christoph Stockert (
see picture at
left courtesy Frederic Secchi).
There still is a compass manufacturer called
Stockert
in Nuremberg (see also
Marching
compasses).
Technical
Data (item at
left):
- Dimensions: 72 x 72 x 11 mm (2" 13/16 x 2" 13/16 x 0.433")
- Divisions: only the cardinal points are indicated (in
German). The position of the magnetic needle corresponding to the
declination in those days (late 18th C., i.e.
approx. 15° west) is painted on the bottom.
The gnomon automatically folds back. To read the
time,
one has to push down its lower end with one's thumb.
Modern
Sundials - U.S.A.
SUNWATCH
First designed and manufactured
by
THE
ANSONIA CLOCK CO., NEW YORK
USA.
(
Patent
June 6, 1922 by George HOLLINWOOD,
THE ANSONIA CLOCK Co., 7th Av. 12th Street, BROOKLYN, NY) but the model
was later retailed by
Outdoor
Supply Co.
after ANSONIA was sold in 1929 to a Russian company (see the
company's
History).
There were 5 versions. Two for the American market, one for
the Australian/New Zealand market, one for the British market and one
for the Canadian market. The sundial base plate has 3 scales for
telling time in 3 places with different latitudes. The inside cover has
a chart listing 42 cities in the USA and their respective degrees
latitude, longitude and clock time in minutes to add or subtract from
sun time. The brass gnomon is fitted into a crevice in the base plate,
to be pulled out when needed. The various latitudes are etched into the
base of the gnomon for easy use. The Sunwatch is enclosed in a brass
case with a push-button catch at the base (Source: Description by
www.BONANZLE.com).
(Pic.
abore:
advertisement - click for enlarged view)
BOYD
SUN-TIME
PROFILE - This system was patented in 1950 by Francis O. Boyd
und John E. Johanson and manufactured by the JOHANSON
MFG.
CORP BOONTON,
NJ. (click
HERE
to view the patent's fig.). This item features e retailer of this item
was the well-known
Compass -
Instrument and Optical
Company,
268 Fourth Ave. New York 10, N.Y.
Above:
the white element on top of the dial is the gnomon.
It is to
be orientated in such a manner that the crest doesn't cast a
shadow on the flat base.
Below: the manufacturer's signature
 |
The table
of
longitudes
above the sundial
Latitude setting
(Click
on the images for enlarged views)
|
Map of the U.S. with the declination curves in
red
Declination setting
|
Technical
Data
- Case Dimensions: 2" x 1 1/2"
- Compass diameter: 1 1/8" (30mm)
- Metallic case
- Sundial with two possible readings: Standard and Daylight Saving
- Table of longitudes for mainland U.S.A.
- User's instructions : 6 pages ( facsimile can
be ordered).
Concealed under the blue tag of Compass
Instr. &
Opt. Co.:
"Precision Made By
Johanson Mfg. Booton etc..."
|
Austria:
W.A. (logo:
sunrise)
PROFILE - Unknown manufacturer with the initials W.A. and a logo
featuring a sunrise. The month names are indicated in Austrian
German: Jän[ner] for
Januar
(January).
To read the time of the day, the instrument is to be
held
flat. Make sure that the 12 o'clock figure of the disk is facing the
geographic (true) North mark of the compass. Turn the instrument until
the needle's blue north end faces the tiny declination arrow
(between 11 and 12). Place the gnomon bearing bar (missing on this item
- see a sketch of a possible component
HERE) onto
the notches of the locking ring and erect the gnomon. Its
shadow
tells the sun-time at the location - not the exact time in the country!
The clinometer is used to measure the elevation angle of the sun or the
moon etc. above the horizon by aiming at it with the two notches
aligned.
Date of design/production: Magnetic North being indicated on
the
disk half-way beween the figures 11 and 12 and since 1 hour
equals
15 degrees (360°/24h), the declination
equals approximately 7
deg. west, i.e. 1910 for Austria's capital Vienna (result
computed
with the
online programme of
Canada's Natural ressources
Dept.).
Note:
This
item's former owner added
by hand corrections in red maybe to take into
account some a
change of location.
Bottom
left: The manufacturer's
initials and logo
|
The clinometer
(90°)
Pictures courtesy M.
Allouche |
The hour disks
Click on the images for
enlarged views
|
Technical
Data
- Diam.: mm
- Thickness: mm
- Hour Disks: 5, printed on both faces for 10 periods of the year
- The sunrise logo is almost identical to the Busch Rathenau's
own logo
|
This description is far from being complete. See some
general information in the category Nautical Compasses/China.
Further details are still missing.
Thanks for sharing your knowledge with us.
-
Horizontal Sundial with
vertical pin gnomon
(
Reproduction
- click on the link).
-
Vertical Sundial
(Diptych)
Click on picture.
above for detail view of sundial and explanations of signs
|
The
compass dial has
no divisions. Only the needle's south half ist painted red.
Technical
Data
Material: wood and paper, lacquered
Dim.: 75 x 65 x 21 mm
|
Calendar
- Centre disk: 12 month names
- Outer circle: "30" month day names
|
Both
left and right
sides are
covered with text.
Text: ?
|
Inclining
Sundial
Description of the sundial panel and the compass's
surrounding area based on the explanation given in J.
Klaproth's
famous booklet
Lettre
à M. le Baron A. de Humboldt,
1834 (online
HERE):
- The Adjustable Panel (sundial):
Above the gnomon: one illegible character; below the
gnomon, the sign "
bei"
(north) and three concentric circles :
- Inner circle: the 12 signs
cycle
- Middle circle:
figures 1-12, repeated twice,
clockwise.
- Outer circle: (?)
- The Compass's surrounding Area (three concentric circles):
- Inner circle: the
eight kua
or trigrammes of Fou Xhi (compare with
the instruments displayed in the category RELIGION).
- Middle circle: the same in
classical characters (N-W in
red).
- Outer circle:
the 24 Tcheou
cycle (see cat. NAUTICAL
compasses).
Technical description - Inclining sundial - The compass has a grey
metal base on which the meridian line is marked. It has a steel needle,
reddened at its South end, and is covered by a glass plate, held in
place by a black ring. Beneath the hour-plate is a toothed ratchet
scale with 13 divisions, marked in black. A brass strut attached to the
back of the hour-plate is set in this scale to position the hour-plate.
The front has an hour scale for Chinese hours. Two red characters
within this scale indicate that the compass should be turned to the
North. There is a brass rod gnomon that folds flat when not in use, to
be set perpendicular to the hour-plate. On the reverse side of the dial
are nine Chinese characters (three in red) giving the name of the maker
and the area from which he came.
Technical
Data
Material: wood and paper, lacquered
Dimensions: 120 x 58 x 18 mm
|
|
On
either side of the
notches, probably city names. Additionally, four signs in red ink
|
Rear
side:
- three signs in red
- six signs in black
|
This instrument is signed by J[oseph] Jackson who was working
between 1735 and 1760. It was
probably manufactured in about 1750, this assessment
being
based on the style of engraving.
Principle: Maker's or
user’s instructions for sundials of this type are not known
to exist. Basically the crescent gnomon has to be adjusted to the
latitude of the place where it is being used. An adjustment is also
made for the time of year, using the calendar scale, and the instrument
is levelled using the levelling screws and spirit levels. Normally
these kinds of dials do not have a compass, being regarded as
self-orienting, since if the adjustments mentioned are made, the shadow
of the tips of the crescent will fall on the hour scale and the
instrument can simply be turned until this happens. Possibly the
addition of a compass was so that the magnetic variation could be
checked against a noon reading. Examples by English makers are rare, as
this design never seems to have been as popular in the British Isles as
it was in continental Europe.
(Source:
Gloria Clifton, The Royal Observatory, Greenwich, UK)
The exact function of all parts cannot be entirely described.
Your help is needed.
Crescent
sundial signed
J. Jackson, London
(c. 1750)
Technical Data
Dimensions:
12" across x 10" 3/4
tall
Ad for a/c avionics instr.
|
View from
aft
Detail
view of
the calendar around the base plate
(Click
on the images for
enlarged views - All pictures courtesy Scott Meyer)
|
Detail
view of the compass dial. The needle's
pivot
straddling on top of the central level tube is a unique feature.
The maker's signature and angle values
The crescent-shaped hours scales (top ends)
|
Detail
views of individual scales
Hour scale (minutes):
Zodiacal signs
The vernier on the latitude scale
The months scale on the gnomons holding crescent
|
TECHNICAL
DESCRIPTION
(for USER'S INSTRUCTIONS see
Part 2,
bottom)
(Note
- An equinoctial
sundial in a hunter-type pocket compass case is displayed at page top).
This system is assumed to
have been developed in France in
the late
17th C. by a clockmaker living in Auch (South of France) called Rugend.
Like many others, he was forced to emigrate to Germany because of the
religion wars and maybe changed his name into
Rugendas
since we
find
compasses made in Augsburg which are signed
Rugendas.
(Quoted after
Mesures du temps
et de l'Espace -
OLF,
1970)
The typical Augsburg dial consisted of an octagonal or square base with
a large compass set in the centre. The equinoctial ring of the dial was
hinged to the base plate and its gnomon was a narrow rod set at the
centre of a pivoted bar lying across the West-East diameter of the hour
ring. The latitude of the hour ring was set by means of a latitude arm
hinged to the base plate, against whose scale the angle of the
equinoctial ring could be set. The latitudes tables were generally
engraved on the underside of the compass bowl but sometimes printed on
a paper glued inside the lid of the box.
The
magnetic
declination was sometimes
indicated with the letter
E (emendor) on the dial of
some compasses like this Vogler sundial (see pic. at left - courtesy
James P. Frellsen - click to enlarge). Since the declination was
approx. 10°
East in the late
18th C., the E-E line indicates the magnetic North-South
axis.
Note: The cardinals are indicated in Latin Language. S = Septentriones
= North!
We display below two typical items: A mass-produced Vogler and
a high-quality Joseph Anton Schöner.
Andreas Vogler was the brother
of Johann Georg Vogler who had started a
shop in Augsburg in 1740. Andreas took the business over at his
brother's death in
1765 and continued until the 1790's. He died in 1800. They had
specialised in poorly executed, cheap mass production items with crude
design and little accuracy.
(Source: Higton, H. -
Sundials
– an Illustrated
History of Portable Dials
© 2001)
Picture:
print out of
La GNOMONIQUE pratique, Fig. 68
(Click
on the drawing for
an enlarged view) |
German
pocket instrument
(Picture
courtesy Jaypee -
Click on the picture for
an
enlarged view) |
Reverse: the latitudes of a few cities* and Andreas
VOGLER's signature abbreviated
"And. Vogl".
Eleva Poli = Elevatio Poliarum (latitude of cities)
Augsburg Paris 48, Cracau (Kracow), Prag (Prague) 50, Leipzig
51
|
Luxurious
gilt instrument
View from the
side
(hour
ring
fully erected for the photograph)
Pictures
courtesy Efim Tulchinsky -
Click for enlarged views |
Top
view showing the
maker's signature: Joseph Anton Schöner
The dial features cardinals in Latin language (see Miscellaneous /
Cardinals / Latin)
The pendulum ensuring an horizontal position:
|
City
names on
reverse:
- OFEN is the old German name of Budapest. Pest is the Hungarian form
of the former slav name Pecs meaning "oven". This was probably the safe
place on the other bank of the Danuve river where the city's bread used
to be baked.
- St
Maura
was a fortress near Istanbul
(picture
copyright
www.vintage-maps.com)
Other names: Ceftalonia,
Spalatro: see WIKIPEDIA
Note: A dash was engraved above a letter in the place a
following "n" or
"m" (like in Dresde-n, Amsterda-m and Cölle-n =
Köln/Cologne) left for place reasons.
|
Other
equinoctial
compasses
 |
|
High
precision
instrument with two levels and three levelling screws made by F.
BARKER & Son (1919).
The latitudes scale reaches from zero to 90° so that
this instrument can be used from the equator to the poles. |
Instrument with one level sold by SECRETAN
(ca. 1930) but probably made partly by Houlliot (dial and needle) |
Instrument built by HOULLIOT
in the middle of the 20th c. |
|
PROFILE - Nicolas BION (1652-1735) was a French mathematician. His shop
was located
in Paris, Quai de l'Horloge du Palais.
He wrote a famous book on mathematical instruments called
Traité
de la construction et des principaux usages des instruments de
mathématique and
built Butterfield-type
compasses.
WARNING
- Beware of
FAKES!
(click
on link for
pictures)
Several major museums have confirmed that contemporary
reproductions are
currently available - usually on eBay. These are only worthless museum
gift shop
items and not original antique items. You can easily recognize
them by the gross engraving of the latitudes (40-50-60) on the gnomon's
adjustable blade. Send us pictures if you are unsure.
 |
N.
BION showed in it a sundial with
his name as the maker on page 362. |
 |
For
a description in English, see part 2 below.
Note:
This exhibit doesn't
belong to the Online Compass Museum. This picture was part of an
auction's catalogue (1984). |
PROFILE - Michael Butterfield (1635-1724) was a British clockmaker who
settled in Paris
about the year 1663. He worked for the royal court of France and was
appointed engineer to the King. He opened in the district
faubourg
Saint-Germain, in the street
rue
Neuve-des-Fossés, a
shop for precision
instruments. His shop's sign read
AUX
ARMES D'ANGLETERRE
(at the sign of England's
coat of arms, 1st mention in 1677). Russia's Czar Peter the Great
visited his shop in 1717 and
ordered a great quantity of dials made of gilt copper. After
Butterfield's death
in 1724, the sun-watch type he had been manufacturing and selling was
copied by many european manufacturers.
Description
The Butterfield dial is a type of semi-universal horizontal dial, that
is, a horizontal dial which can be used in a number of different
latitudes, but not in the full range from 0° to 90°. It
is
generally either octagonal or oval in shape and is almost always marked
with three or four different hour scales, each of which is marked with
a specific latitude. The essentials of the Butterfield sundial are
a dial plate engraved with a number of different hour scales serving
different latitudes, a compass, and an adjustable gnomon. The gnomon is
marked with a latitude
scale and it can move within the bird index which marks the latitude
angle against the scale.
It was not B. who originally designed these instruments. Examples are
known which clearly date from before the time that Butterfield began
working in Paris. Earlier items known were made by
Roch
Blondeau (dated 1673), but also by Timothée Collet.
The fact that Butterfield used a bird-shaped pointer on the gnomon
probably made his sundials highly fashionable and he soon achieved a
monopolistic situation on the market.
(Source:
Higton, H.
“Sundials – an Illustrated
History of Portable Dials” © 2001)
Pictures below: Late 17th, early 18 Century
silver horizontal
"Butterfield Sundial"
Description
A pantochronometer is a Horizontal Magnetic Dial. The
rotating card is automatically pointing
to the magnetic pole. This system was already in use in the 18th C.
Collectors & museums refer to pantochronometers as "Magnetic
Dials". The term, "pantochronometer" meaning combined Sundial &
Compass, was first used late 18th century,
early 19th century, probably in the UK, possibly by Essex
& Co (Charles Essex ? 1824-1828, London)
19th century versions. Most makers referred to, or labeled them as,
"Magnetic Dial" {Porter
for example}. Few others referred to, or labeled them as
pantochronometer, usually, but not always, with EOT tables (Equation of
Time).
Magnetic Dial Problems
- The usage is limited to the latitude determined for the dial.
- Declination / variation could not be altered/adapted. All
sundials must be oriented to TRUE NORTH, never magnetic north. When
made, declination / variation values would be applied to the card. Over
time (less than 10 years) declination / variation values shift (either
west or east) thus rendering the dial inaccurate.
|
Pictures
courtesy weezie24
|
|
Technical
Data
- Dia.: 57 mm
- Height (without lid): 37 mm
Maker: Stockert, Germany, late 18th C.
(probably Johann Paul - see also above
German sundials)
(Click
on the pictures for
enlarged views) |
PROFILE - ... (C. R.) was a French sundial maker ... ?
|
|
|
Technical
Data
- Diameter: 55 mm
- Depth (with lid on): 20 mm
- Weight: 34 gr
- Material: Gilt light alloy
France, late 19th C.
(Click
on the pictures for
enlarged views) |
(Click on the pictures for
enlarged views)
|
Russian
pocket sundial with domed glass
|
Technical
Data
- Diameter: 40mm
- Depth: 14mm
- Weight: 18gr
- Early 20th C.
- Cardinals written in old Russian (compare with
Miscellaneous /
Cardinal points / Russian)
|
Picture courtesy private
coll.
(Click on the pictures for
enlarged views) |
 |
RÜTER
UHR (watch)
Type no. 5 - Berlin
Technical
Data
- Dia.: 50mm / 2 in.
- Height: 25mm / 1 in.
- Materials: the gnomon, two
adjustable magnetized razor blades
and the disk were attached
together with a pressure button and placed on top of a
grammophone needle (click
on link for picture, "Neues Universum").
- Manufactured: Summer 1946, shown in a weekly news (Wochenschau) footage.
Dwg. at left: Principle of the two hour rings for Winter and
Summer hours
(Winterzeit WZ and Sommerzeit SZ) and the magnetic declination
scale. User instr. and techn. descr. in German available (s.
SHOP). |
PROFILE - C. R. (name ?) was a French sundial maker
|
|
Technical
Data
- Diameter: 55 mm
- Depth (without lid, gnomon erected): 22 mm
- Weight: 35 gr
- Material: brass case, paper dial
France, late 19th C.
(Click
on the pictures for
enlarged views) |
PROFILE - Johan Henrik L'Abée-Lund was a Norwegian engineer.
He manufactured this compass from approx. 1922 to the late 30's.
The
name
Uhr-Kompass
means "watch compass", and was meant quite
literally: It could be used as a sundial, with the use of the
table on the backside. The red little ant was a part of a promotion
gimmick. In these days
every product should have a marketing slogan, and for this compass it
was "
Kjøp
kompassen med Mauren
i syd" i.e. "Buy the compass
with the ant
pointing south", referring to the well
known fact that in the woods you can find approximately South by
looking at what side of the trees the ants build their hill.
(Quoted
from the website
http://www.purgatory.net/kornelia/compass/compass.htm)
Picture at right: the south-pointing red ant
COMBINED
INSTRUMENT:
COMPASS (based on the sun's position) & BINOCULAR
Origin: Germany (ca. 1930-1940), model
FAVORIT
/
D.R.G.M. (reg. trade mark).
Folding binocular with sundial. A device shaped like a bottle opener
serves to lock in folded position the small spring loaded lenses.
User's instructions for the sundial-compass: The dial shows the hours
of the longest possible summer day in Northern Germany (i.e from 3 in
the morning to 10 in the evening) together with the cardinal points. To
orientate the compass, one has to rotate the arrow so that the current
hour (indicated by a watch) appears in the arrow's fork end. One turns
then the compass with the arrow head pointing towards the sun. Example:
at noon, the sun is in the South.
Like on all other
opera
glasses (shown in the category
OTHER COMPASSES), there is a
mirror on the face opposite to the dial.
 |
Click on the picture for enlarged view of dial |
Technical
Data
- Length folded: 105 mm
- Compass Diameter: 40 mm
Indications on the dial:
- Sonnen-Uhr & Kompass (sundial and compass)
- Abends (afternoon)
- Morg. (morning)
- Tourist / D.R.P.a. (hiker)
Concerning the meaning of Tourist
in German in
those years, and the abbreviations, see MISCELLANEOUS / GLOSSARY.
|
Pocket
Hunter Sundials
Hunter type compass types with foldable Butterfield-type,
bird-shaped gnomon.
It
appears in a 1932 catalogue of the French company S-L (see
category Pocket
Compasses) but was manufactured by
Houlliot.
Pendant hold closed with the neck-lace chain
 |
|
Replica
of an antique
instrument
Technical data
- Dimensions: 50 x 38 x 13 mm
- Weight: 35 gr
(Click
on the pictures for
enlarged views) |
GENERAL INFORMATION about astronomy and sundial technique necessary to
understand their functioning
The
Physical Principle
A sundial is a reduced representation of the
Earth. The sun's light rays impact the instrument exactly like
the globe. This is why the sundial first has to be
orientated. This can be done by means of the
integrated
compass but one must take the magnetic
declination
(the difference
between Magnetic North and True
North) into account. The gnomon (
see
definitions below)
must point towards the Earth’s celestial pole – or
– in line
& parallel to the Earth's axis, towards the North Star* ... if
one could see it during the day hours!
On some dials bult in the18th c. the declination was indicated by means
of a additional line between two letters E (for
emendo
=
correction in Latin - see pic. at right).
*
The North
Star
and Latitude
The
angular height of the North Star {in degrees} above the horizon is the
same as your latitude in degrees. The North Star is on the horizon at
0° latitude and not visible South of the Equator but even at
10° N. latitude {and below} the North Star may not be visible
on even the clearest nights due to atmospheric haze.
The
sundials'
components
The Gnomon
– Blade, Pin or String
The hour is told by the
shadow of a device called
a
gnomon.
There are three different types:
-
Pin Gnomons
are fixed – whereas,
blade
and
string
gnomons can
be fixed or adjustable.
On fixed gnomons, the pitch or angle is the latitude at which the
sundial was made.
Sundials used at higher latitudes have a steep angle. Sundials
used near the equator – or lower latitudes have a
shallow angle.
-
Adjustable Gnomons
can range anywhere from 0° to 90° (example: Barker,
above).
-
String Gnomons
- The string can be fixed for one mean latitude or adjustable
(example: German sundial above).
Fixed
Blade Gnomons usually
have a simple hinge to lay them on the side when closed. Their slope is
a mean value for a limited area (Mediterranean, Central Europe) and
doesn't allow precise time telling.
Adjustable
Blade
Gnomons
Such gnomons generally consist of an adjustable quadrant
engraved on one side
of a
folding hinged blade gnomon supported by a bird-shaped fitting
(duckling).
The dial chapter includes several (2-4) sets
of engraved
or painted scales
alternating in Roman and Arabic numeral made for different latitudes.
This sundial type is adjustable for latitude
by increasing or
decreasing the angle of the blade gnomon against the bird's
beak . The
shadow's border line on one of the appropriate dials for the different
latitudes determines the actual time.
The compass
Pocket sundials incorporate a very simple recessed compass.
The
Latitude Scale
On nautical or professional equinoctial compasses for explorers, which
have to be usable in the entire world, the latitude scale must be
representative of any location on Earth. It is thus graduated
from 0° to 90°, covering a full
hemisphere.
On pocket sunwatches, it just needs to cover the area in which it is
intended to be used. The span typically measures hence only about 20
degrees in Europe (
38-56
on the German compass above).
This is enough to cover a
zone reaching from Portugal to Scotland or 30-50 in the US
(New Orleans to Quebec).
TELLING THE TIME
Hour chapters
are usually divided into 5 ~ 15 minute increments.
Read left to right - from morning hours {4 am on the example at left}
to afternoon hours {8
pm}
with 12 (noon) typically in the middle (South). If a sundial is set-up
correctly – the shadow cast by the gnomon onto the hour ring
will give the time of day.
Note - Sundial Time is
Different than Watch Time!
A sundial disregards time
zones. These change
every 15
degrees (time meridians), this value resulting from the Earth's
circumference (360°) divided by 24 hours (one day or
one Earth
rotation). Sundial Noon is defined as when the Sun is directly
overhead, not when
a watch says it is noon. The difference here is the user's distance
(east or west) from a time meridian {longitude}. This
difference can be
as much as 30 minutes if you are exactly between two time meridians.
Since there are 1440 minutes in 24 hours, one minute equals (1440/360)
four degrees of longitude (15 seconds per degree). The Prime Meridian
or 0° longitude runs through Greenwich, the opposite,
being
the International Dateline at 180°. The full hour is thus only
to
be read at places located exactly on a multiple of 15°
i.e. 30, 45, 60, 75, 90, 105, 120, 135, 150, 165 and 180
degrees
west and east). Since the Earth (seen from above the North pole)
rotates counter-clockwise, the sun apparently moves from east to west.
Within a defined time zone, an observer has to add one minute
per four-degree step to (or subtract from) the next
"full-hour spot", depending on whether he stands west
or east
of this location i.e. before or after the sun traverses it at
noon. Example: an observer located at 92°
west
longitude must add 8 minutes to sundial time to correct to
clock
time, Another one located at 88° west longitude would
have to
subtract 8 minutes.
Moreover, many time meridians follow the political borders of
countries.
Another factor to sundial time is the
Equation
of Time
where in some
months of the year, time appears “fast” and in
other months time appears “slow”, this being caused
by the Earth's elliptical orbit around the sun.
Ancient
Definitions of
the Hours:
There has been several methods for counting the duration of a day:
-
Judaic or antic
hours: 12 hours from sunrise to
sunset and 12 hours from sunset to sunrise. They were only twice in the
course of the year of equal length, on March 22 and September 22
(equinox)
-
Italic
hours: 24 hours of equal length from
sunrise until the next sunrise
-
Babylonic
hours: 24 hours of equal length from
sunset until the next sunset
-
Astronomical
hours: 24 hours of equal length
counted from noon until noon on the next day.
USER
DIRECTIONS
A - Equinoctial Sundial
1} Place sundial on a flat
level surface = parallel to the
horizon (if applicable: acting on the screws to center the
level
bubble).
2} Set the latitude of the hour ring (example: London = 51°,
New Orleans 30°, Toronto 45°).
3} Lift the gnomon to 90° angle from the hour ring (sometimes
also called chapter ring).
4} Orient the magnetic needle North to local
declination.
B
- Base Plate
- Sundials with String (2a) or Blade (2b) Gnomon
1} Place sundial on a flat level surface.
2a} STRING - Erect the cover lid vertically so that the string is
pulled
tight with no sagging. If applicable, set the string to the relevant
latitude of your current location. Select the nearest
city indicated on the reverse side.
2b} BLADE - Adjust the blade's scale against the bird's beak according
to the latitude of the nearest city indicated at the underside.
3} Orient the magnetic needle North to local declination
.
BIBLIOGRAPHY
- Gatty, Mrs. A. K. "The Book of
Sundials." - Edit by H.K.P. Edens & E. Lloyd.
© 1872 - Fourth ed. 1900
- Gouk, P. "The Ivory Sundials of Nuremberg 1500-1700”
© 1988
- Higton, H. “Sundials – an Illustrated History of
Portable Dials” © 2001
- Lloyd, S.A. ”Ivory Diptych Sundials 1570-1750”
© 1992
- Marshall, R.K. “Sundials” © 1963
- Waugh, A.E. “Sundials – Their Theory &
Construction” © 1973
Ancient French books dealing with the theory and
technique of sundials:
- Traité de la CONSTRUCTION et des principaux
usages des
INSTRUMENTS de MATHEMATIQUES by Nicolas BION (1709, see below)
- Traité de GNOMONIQUE PRATIQUE by Dom
François Bedos de Celles (1709, picture at right),
- Traité
de la
Construction et des
principaux usages des instruments
de
mathématique (N.
BION)
- Traité d'HORLOGIOGRAPHIE de Dom Pierre de Sainte
Marie-Madeleine (1701).
Contemporary books addressing more collectors and describing
items
displayed in Museums and private collections:
-
Anciennes
INDUSTRIES scientifiques et artistiques DIEPPOISES
(55 p.) 1904, by Ambroise MILET, chap. II: Cadrans
à boussole.
-
LES MONTRES SOLAIRES
- Booklet of about
30 pages
written in 1932 by Commandant VIVIELLE, Head of the French Navy's
Library and private collector. This booklet gives valuable information
about the different sundial types and the life of the makers.
(Photocopies
can be ordered),
-
LES
INSTRUMENTS DES
SCIENCES (Sté fr.
du Livre, 1966),
-
MESURES
DU TEMPS ET DE
L'ESPACE (Off. du Livre,
Fribourg, 1970).
We reproduced here some pictures of items seen in the older ones and we
used some technical definitions and historical facts concerning the
items. You will find find more information about this topic (in French
and German) on the following website:
Gnonomik
This department
only deals with portable sundials equipped
with a compass. We describe in Part 1 the different types developed
between
the 17th
and the 19th century.
You will find technical background information in the 2nd
Part. Concerning the non-magnetic military
sun compasses
we recommend the excellent essay
by Malcolm Barnfield The
Sundial Goes to War on the
website
Sundials.
These two-fold ivory sundials are called Dieppe-style
because they were originally developed and mass produced by Charles
BLOUD in the northern French city of DIEPPE (Normandy) from 1666 on.
His brothers (or sons?) Gabriel and Jacques continued the trade and
were first imitated by Ephraïm Sénécal,
then by Jacques Sénécal (see table 2, center
photograph.
The two most important manufacturing cities in Germany
were Augsburg (s. Equinoxial
systems further below) and
Nuremberg. In this city, sundial makers first
produced diptychs
made of ivory like in France (Dieppe) and later simple one made of
paper and wood.
A well-known manufacturer was Ernst Christoph Stockert (see picture at
left courtesy Frederic Secchi).
There still is a compass manufacturer called Stockert
in Nuremberg (see also Marching
compasses). 
SUNWATCH
The magnetic
declination was sometimes
indicated with the letter
E (emendor) on the dial of
some compasses like this Vogler sundial (see pic. at left - courtesy
James P. Frellsen - click to enlarge). Since the declination was
approx. 10°
East in the late
18th C., the E-E line indicates the magnetic North-South
axis. 
TELLING THE TIME 
Ancient French books dealing with the theory and
technique of sundials:
