Begin restoration of zodiac precession, and year
We now turn to the
restoration of two major complications within the tellurian. The first is
the precession of the zodiac. This
is depicted by the moveable lower silvered band engraved with the signs of
the zodiac and surrounding the tellurian, first photo below. Pouvillon had
described this in an interview for a Paris newspaper in 1953 and the
function was also described by Mr. Bernard Miclet in
his article published in the French antiquarian horological publication,
Bulletin of A.N.C.A.H.A.
Both of these sources were very specific about the existence and function of
this complication in that the lower silver band rotated once in 25,806 years
to mimic the zodiac precession and that Pouvillon achieved this through the
use of “twelve wheels and twelve pinions”. This function has been referred
to as 'the slowest hand in the celestial clock'. The upper silvered band is
fixed and is marked in 360 degrees making the comparison between the two
obvious. This upper graduated ring is also used to track the annual movement
of the tellurian mechanism as it rotates with the Earth / Moon system
allowing one to track the Sun’s apparent motion through the zodiac.
The second complication is the year indication which is
displayed through an existing aperture in the enamel tellurian dial. That
aperture was covered up when we received the clock. I will discuss this
further when we begin the fabrication of that complication. The two
complications are being described simultaneously because both are driven
from a common source and so were built at the same time.
As found, the zodiac
ring was clearly mounted in such a way as to be moveable. The ring is held
slightly loosely between three points, see arrow showing one of these
points, second photo. However, all evidence of the mechanism to achieve the
very long rotational zodiacal precession was missing. There were no wheels,
no obvious mounting points for these wheels or plates where these mounting
points could have been located. All we had were a few empty holes in the
bottom of the tellurian dial support structure. The third photo shows one of
these holes. So the question now becomes, was this complication ever built
or did Pouvillon engage in a bit of puffery? Did Mr. Miclet really observe
this complication in 1985 when he observed the clock for his article or did
he simply take the information given in the interview for the Paris
newspaper in 1953 as fact and repeat this in his article? We decided to
reinstate this complication with the proviso that any work we performed was
fully reversible with no alterations to the original artifact, a
rule we have observed throughout the entire project. Also the complication
would be made in such a way as to be invisible to anyone who had taken any
of the photos we have up to this point so as to not conflict with the
pictorial historical evidence we have to date. We also made sure that the
complication conformed to the “twelve wheels and twelve pinions” asserted by
Pouvillon. It turns out that this combination of wheels mathematically
results in a surprisingly simple set of wheels using common tooth counts as
follows with the first eight wheels being identical. Our initial drawing is
shown using the formula below:
48 x 48 x 48 x 48 x 48 x 48 x 48 x 48 x 46 x 44 x 34 x 24
24 x 24 x 24
x 24 x 24 x
24 x 24 x 24
x 20 x 20 x
16 x 16
= 4128.96. The input ratchet mechanism
divides this by four = 1032.24 for the input
18 leaved input pinion to the 450 toothed
ring gear. That pinion turns 25 times for
each complete turn of the ring gear giving
1032.24 x 25 = 25,806, the number of years
for the ring gear and thus the zodiac ring
to make one complete turn to indicate the
precession of the Earth on its axis.
This is the first wheel design, using very small sized wheels in the train.
One can see when the dial is placed upon the drawing the wheel train
disappears. The same is true for the tellurian base. This design has the
advantage of totally hiding the reduction portion of wheel train. Of course
there are a few additional wheels that cannot be tucked under the dial,
these feed the reduction train. By hiding the restoration to this extent we
keep the look of the clock as much as possible to the way it was found.
On the other hand, if Pouvillon really did
complete this system and used the 12 wheels as described, it is unlikely he
would have purposely hidden them. The entire clock is designed to show off
the wheels and their complexity. So we also explored this design using the
same ratios but with larger wheel dimensions.
These pictures show our second approach.
Even with the larger wheels they are fairly hidden under the tellurian
structure from above as shown in the second photo. Next a view from below
the tellurian support ring.
Although these show more than the first
design, one must remember that the wheels are not actually sandwiched
between the enamel dial and the lower extant spider support structure. The
wheels will be mounted on an identical looking structure below the
tellurian so when one looks directly from below the wheel train, no matter
how designed, will be in full view.
The fabrication of the wheel train begins. First the they are scribed in the
brass blank in a pattern to minimize waste. Next the initial drive wheel
train wheels are cut and then the 30 wheels that make up this train, the
complete train is 36 wheels, see schematic below.
What is shown are actually wheels and their associated pinions. One might
ask why the pinions are made of brass rather than conventional steel
material and the answer is that this train moves so slowly that this is not
a consideration. Another advantage to using brass in conjunction with the
second design option employing the larger scale is that the pinions will
also be spoked in addition to their mating wheels. The two outer rings of
wheel blanks are used for the zodiac precession. The center wheels are
involved with delivering the drive to that large reduction wheel set and are
also used for an additional complication, the year indicator, to be
We now begin to fabricate the ring gear that will drive the zodiac band. The
ring will have 450 internally cut teeth and is relatively thin. Considering
this, the material must first be annealed to relieve the natural stresses
that are present in all modern rolled brass. The raw metal stock is heated
in a furnace and then slowly cooled. If this is not done the ring will
distort under the machining process. After the ring is finished, it will be
re-hardened. Next the disk is cut from the brass stock. Normally the round
portion is what is used for a conventional wheel and the surrounding
material disposed of, but here the reverse is true.
The blank is quite
thick, about ¼” or 6.2mm. However, Buchanan will not use the entire
thickness for the teeth. The finish form of the ring requires a recess which
can just be seen above and below the cutter in the second photo. The actual
tooth thickness is more on the order of 2mm. Next is a close up of the
cutting tool used to make the interior teeth. It is the same used for the
epicyclical fly fans on the commission
astronomical clock, also see video below to see the cutting tool in
First photo shows the two blanks for the
zodiac precession and year indicator gear rings with their fine teeth. Each
one has 450 internally cut teeth.
The outer portions of the square blank is
next trimmed and
the next photo shows the ring
attached to a plastic disc. That disc is what is attached to the lathe
chuck. This is necessary because the ring itself is too delicate to be
directly gripped by the chuck.
The ring's shape is further refined. The
next two photos show the snug fit between the toothed drive ring and the
zodiac band. That ring will be flush with the lower edge of the zodiac band,
remaining unseen from the outside.
now turn to the year indication complication. The tellurian dial
originally had a square aperture in the January sector which indicated the
year using the last two digits. We have ample photographic data of an
tellurian dialthat shows this.The original tellurian dial as well as many of the tellurian
components was not created by Pouvillon. We have evidence that the dial was
made about 1790 from another, identical example and it had a removable second digit
to make the dial useable when the century turned from the 1700’s to the
1800’s and so needed to have the second digit in the year changeable from
‘7’ to 8’. The Dial has the first digit of the year permanently fired onto
the surface just like in our example. The second digit was removable with the remaining two visible
through the aperture indicating 00-99.
As received the aperture on the dial was closed with a white filler
material. Here we begin to get into some pure speculation. On the one hand
Pouvillon was anxious to have as many complications as could pack into his
clock. Furthermore this indication was not repeated anywhere else within the
movement and if Pouvillon received the tellurian structure intact, it should
have had this complication already present and ready to go. He would have
had every incentive to use it. On the other hand, what if the tellurian was
not complete and presume that the year date ring and maybe the associated
driver were missing? In this case Pouvillon may have taken the easy way out
and simply dispensed with the effort to recreate this complication and
covered up the aperture. We do know after the fact that creating this ring
took quite a bit of time and skill; surely Pouvillon had the skills but we
do not know if he actually did it. Of course a third alternative could be
that this complication was lost as were many other parts during events after
Mr. Pouvillon’s passing and as a result the aperture was then closed up.
The first two photos
show the date ring laying on the underside of the tellurian dial. The dates
will show through an aperture on that dial which we now have opened after
removal of the white plug.
The first two photos
show the date ring rollers. These are positioned upon the three existing
brass pillars, last photo. These pillars are also used hold the tellurian
dial feet. The rollers simply slide over the existing pillars.
Numbers are temporarily
penciled on the ring perimeter to check for legibility under the existing
enamel aperture. Furthermore they must be placed in exactly the right
position since the ring will be advanced annually in a single 'jump', so
that number must appear correctly under the dial aperture at the moment the
ring is advanced as it will remain there for the rest of the year. The next
photo shows the year ring gear behind the tellurian dial. When seen from
straight on it is just at the inner edge of the dial.
Next are the two
ring gears as seen from below. The outer one drives the zodiac precession
and is attached to the zodiac silvered band while the inner one rides on the
rollers just below the enamel dial and will show the year within that dial's
Here we see both
ring gears neatly sandwiched within the tellurian structure. Buchanan
commented that the precession of the zodiac is so slow, that in the time
left within our lifetimes, say 30 to 35 years that the zodiac ring would
have moved 1/10th of a millimeter, the width of a fine pencil
line. Of course one will be able to advance the step lever drive to see the
date ring advance one full revolution, that is one century, with each 100 clicks and
so we should be
able to then see the ring move, particularly because it is adjacent to the
calibration ring above it.
Now we see the round plate upon which all of the
zodiac precession as well as the year date ring mechanism will be mounted.
This will later be trimmed to the same design as the four spoked frame which
currently serves as the base for the tellurian. The wheel with the large
hole in the center will fit upon the steel flange shown in the next photo.
Next is a close up of the flange; it screws
into the base plate and one can just see the threads cut into that plate.
Next the wheel is
mounted onto the flange.
The flange is now screwed into the plate securing the wheel in place, yet
still acting as a bush upon which the wheel is free to turn. The entire
reason for this design is the fact that we needed a wheel to revolve right
at the axis point of where all of the orrery’s planet drive tubes intersect
through this hole. The last photo
shows the final machining of the zodiac gear ring, now having an ‘L’ shaped
Buchanan now makes a
‘containment vessel’ from steel wire to hold a steel pinion assembly during the hardening
process. In the second photo he demonstrates how this is fired. Next the
pinion as it was removed from the coil and is now properly hardened.
Next two photos show a second pinion which is fixed upon the same arbor. Afterward the pinions
are mounted in place where the lower pinion receives the drive and transfers
it to the upper pinion which meshes to the zodiac ring gear.
The first photo shows
the pinion edge on. It passes through an open area in the original Pouvillon
orrery support plate which is shown sandwiched to the new plate via the
original pillars supports. Remember that these same pillar supports are also used
for the rollers that hold the year indication ring. The photo actually
obscures the lower pinion upon which the upper pinion, shown, is mounted.
Next we see the drilling operations to secure the wheels to the plate for
the ring drive.
Here we see the wheels
secured into place. Next is a close up of the wheel collets which are made
to look like those from Pouvillon’s original wheels as illustrated in
the third photo.
See video below to view these wheels in motion.
The first photo shows a
brass bush that is inserted between these two wheels as they need to freely
rotate past each other. The following photos shows the entire wheel set needed to
drive both the zodiac precession and the year date ring.
Now we begin to
fabricate the feed mechanism needed to drive both the zodiac precession ring
and the year date ring. This will be accomplished by a ratchet feed
triggered by the arm of the innermost planet Mercury. We had to choose this
planet as it is the one at the top of the orrery planet stack and is
therefore closest to the mechanism needed to trigger the zodiac and year
rings. The first photo shows the initial rough components. The next photo
shows an interesting design. The lower cylindrical structure mounted to the
base plate is a bearing that fits into the upper gear above. This is
necessitated because the other end of the arbor shown here is attached to a
ratchet drive wheel. The width of the plate is
too narrow to accommodate the lateral stresses associated with the ratchet
assembly. In the last photo
we see the wheel, far left, fully inserted upon the base bush.
The first photo shows
the initial rough ratchet feed pawl. Next we see
a first refinement of the feed pawl. The pawl is next mounted and showing
the positioning of the feed pawl spring.
The first photo is an
overhead view of the tellurian showing the original spider structure
sandwiched to the new, and as yet unfinished, plate as well as the year date
ring on its rollers. If one looks carefully one can see the ends of the
arbors which carry all of the wheels shown in the next photo. Next we see
the flip side all of the thirty wheels are now in place, functional and ready
to be spoked out. Also one can see the ratchet arm extended over the impulse wheel. The ratchet itself is tripped by
the small pin on the large wheel just below the lever. That wheel is in turn
driven by the center wheel which turns on a bush surrounding the exiting
orrery support tubes. Later a bracket will be mounted to this wheel which
will engage the support arm which drives the planet Mercury, thus providing
the drive for these two complications.
This is how we are able
to get the needed drive that exists below the orrery ring and tellurian base up
to the zodiacal ring shown here as the outer brass rim. The impulse wheel,
in turn gets a drive above the ring and dial support structure to the date
ring above. The reason we use a ratchet instead of a steady gear drive is
that the year ring needs to be moved in discrete increments so that once per
year the date will flip over completely and be properly displayed within the
viewing aperture at all times. Since the zodiac precession wheel train’s
ultimate output is one revolution every 25,806 years it makes no difference
as to how this train is driven.
Shown here is a schematic of the gear train layout for the zodiac
precession as well as the year date complications. There is a total,
including the output rings, of 36