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Any typos are as a result of direct translation of the
original French.
General
The purpose of the show-days of the month are to give the date
automatically, at the same time as the hour.
Generally have their fact of indicating the days, the months and the day of the
month of the month, i.e. the whole of the precepts which the astronomy gives, to
regulate our social and civil life, which is called the "calendar",
moreover almost totality of the show-days of the month also carry a device
indicating the moon phases.
In one simple day of the month, even automatic, it is necessary at the end of
the month not comprising 31 days, to advance manually the needle or the disc of
the date, in order to update the day of the month.
In one perpetual day of the month, all the changes, at the end of each month,
are made automatically, whether the month comprises 31 days or less.
If the needles or the discs of the perpetual day of the month indicate for
example, today: "Tuesday April 30", tomorrow, without any
intervention, we will read: "Wednesday ler May".
The automatic changes are also carried out between the last day of February and
March first, which it is one year normal (known as "commune") or about
one leap year.
In one year normal, the day of the month indicates: "February 28",
then, the following day: "ler March", while if the year is bissextile,
it indicates: "February 28", then the following day "February
29" and two days later only: "ler March".
The automatic passage from one division to another of the one day of the month
old needle or the actuation of a disc, during the change of day, is generally
not fast.
It usually begins around 22 h. 30 or 23 h. and often finishes 1h1/2 to 2 h.
later.
In certain days of the month however, by a special device, the various changes
(date, day) take place abruptly, by a "jump".
These days of the month are called: "instantaneous days of the month or
with instantaneous jumps".
The simple day of the month
The mechanism of a watch with day of the month is identical,
that the indications of the date, of the day of the week and the name of the
month are shown using needles, or by means of discs carried by the various stars
(stars of the dates, the days and the months); discs on which these various
indications are painted, of which one is visible through a spared
"counter" with the dial.
Terminology:
| With |
Entraîneuse wheel of day of the month |
| B |
Intermediate gear days |
| C |
Intermediate gear day of the month |
| 7 |
Star of the days |
| 31 |
Star of day of the month |
| M |
Intermediate star of day of the month |
| 12 |
Star of the months |
| 59 |
Moon star |
| H, K, J, L |
Correctors |
| F, D, G, E |
Saltires |
| B, C, C ', m |
Fingers |
| R, r' |
Reference mark |
The drawing above shows us the one day of the month old simple mechanism.
The
entraîneuse wheel of day of the month is fixed on the wheel of the hours; it
turns in the direction of the arrow and carries out a turn in 12 hours.
The
intermediate gears, of a double diameter of wheel A swivel freely on a tenon or
a screw to range.
They turn in the direction indicated by the arrows, ä reason of a turn of 24
hours.
Tous.les.jours, towards 22h30 - 23h00, the fingers fixed on the intermediate
gears starts to involve stars of 7, 31 and of the moon obliging a tooth to go up
on the tilted one of their respective saltire.
 
As soon as that the point of the tooth exceeds the top of the saltire, the
tilted one (D ') led star to its new home position.
Since the star advances of a step, the needle or the disc fixed on this one
indicates the next day.
- The fingers can be replaced by a pin, but without possible
adjustment.
- The changes of the day and the date must take place
simultaneously.
- At the end of the month comprising 31 days, the finger
fixed on the intermediate gear of day of the month, actuates the star of the
months, which indicates the next month thus.
- Reference marks R and R ', marked on the wheels A, B and
C, facilitate the correct installation of these wheels.
Conditions of correct operation.
The
star must be adjusted very freely on its fulcrum pin (tenon); it should not
however "toss" on this one.
The disc fixed on star should not "rub" under the dial.
The
tooth of star actuated by the finger or the pin of the intermediate gear must be
close to the line connecting the axis of star to that of the intermediate gear
on which the finger is fixed.
As the tilted ones of the saltire fix the position of star, if the tooth of star
is not in a correct position, it is by decreasing one or the other of tilted of
the saltire that it will be brought there.
The tilted one improved will be polished very carefully; a very weak
"bur" even at the top of the saltire can harm the correct operation of
the day of the month.
The
saltire must be sufficiently armed so that its tilted leads the tooth of star
until its home position.
The
finger will lead a tooth of star until the moment when the point of the tooth
which goes up on the tilted one of the saltire, crosses the top of this one.
The
finger charged to actuate star will not touch to in no case the tooth in front
of which it passes before coming into contact with the tooth located on the
locus of centres, if not the star can advance several teeth instead of one.
The
"slope" of tilted of saltire must be sufficient to lead star.
The tilted one must be polished, if not it can occur one "grippement"
between the point of the tooth of star and the tilted one of the saltire.
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