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Here is the list of the ancient instruments decribed in this
page
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The
astrolabe
The astrolabe exists since
Antiquity (200 before J.C). It was designed by Hipparque. Ptolemee
studied it later in the IIIe century. The astrolabe is a plane
representation of the armillaire sphere. It is buit for a given
latitude. It makes it possible to locate the position of the
stars.
It is made up :
- the fixed "tympan"
on which are engraved the circles wich define the astronomical
positions of the "araignée".
- the "araignée"
: a projection of the sky chart.
- the "limbe" : a
ring graduated external.
It shows the apparent revolution of the celestial sphere around
the Earth and makes it possible to establish the position relating
of the stars to one unspecified moment.
It makes it possible to measure the height of the sun compared
to the horizon and thus to calculate the hour.
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Arsenius's astrolabe (XVIe century) |
The armillary sphere
The armillary sphere, invented
by Hipparque consist of five circles of metal. These varouis
circles represent :
- the ecliptic
- the meridian line
- the equator
- the positions of stars
- the fifth mobile circle carries
two sights at the end of an diameter to carry aimings. In its
center, a small sphere represents the Earth.
The observer can thus represent
the apparent movement of the sky according to all latitudes.
Ptolemee used larger spheres to make measurements. |
The armillary sphere |
The
Octant
This apparatus belogs to the
same family as the sextant. Its name comes from its size : the
angular sector is 45° (a eightth of the circle). It is used
for the measurements of the celestial bodies by employement of
mobile mirrors. It thus makes it possible to determine the latitude
of the observer, one of the corodinates giving the osition of
the boat.
It seemed instruments of navigation
about the middle of the XVIIIe century. |
Octant
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Sextant
Instrument est utilisé pour déterminer la position
géographique de l'observateur. Il était particulièrement
utilisé pour la navigation.
Il a été inventé vers 1730, en même
temps en Amérique et en Angleterre, par le mathématicien
anglais John Hadley (1682-1744) et par l'inventeur américain
Thomas Godfrey (1704-1749).
Il comporte :
- une lunette fixée horizontalement
sur le cadre
- plusieurs miroirs mobiles
Sa construction repose sur les lois de la réflexion de
la lumière. Le sextant a la forme d'un secteur angulaire
de 60°.
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Sextant
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The
gregorian telescope
In the telescope of gregory
a real , reversed image is formed in the principal focus of the
large mirror placed at the bottom of the tube. In opposite direction
of the large mirror and on the same axis, is laid out a small
concave mirror. The real image is an object for this second mirror.
It is thus formed a second reversed real image so what this one
is a right image of the object observed which is increased by
eyepiece. |
The gregorian telescope
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The
compass
A piece of magnetized iron
is aligned spontaneoulsly in the North-South axis. This discovery
was alloted with Chinese, the Arabs and the Greeks. It however
does not seem that the compass was used by Europeans before 1400.
After its appearance, at the beginning of the 15th century, the
compass was not change during more than 300 years. The manufacturers
of instruments of navy were unable to solve the three problems
raised by the compass :
- The magnetic north is not
the true north
- The difficult conditions disturb
the compass
- The iron and the steel of
the hull of the ships causes disturbances
It is only about 1800 that
we solve these problems. |
The compass |
The
roman balance
The roman balance is one of
the instruments of weighing in the past know. Its extremely simple
construction, rests on the principle of mechanics according to
: "the equilibre of the balance depends of the weights of
two heavy bodies acting at the ends of two arms and the lengths
of the arms"
The weight, advanced or moved back along the divided stem, fact
balances with the heavy bodies suspended on the hook. After its
appearance, at the beginning of the 15th century, the compass
was not change during more than 300 years. |
La balance romaine |
The
hour glass
Approximately 3000 years before
J.-C, apppeared in Egypt the "clepsydres", or clock
with water. Later, at the XIVe century, the hour glasses are
usually used. These apparatuses measure time by the flow of a
fluid, water or sand. They do not make it possible to determine
the hour but are used for its conservation during a more or less
long time. They are thus in fact the first chronometers. The
precision of such instruments is always very weak, but sufficient
if the measured time is short. Now, the hour glasses are used
than on a decorative basis. |
the hour glass |
The
compass
The compass is an instrument
of layouy or measurement made up of two articulated branches.
It is used in navy to calculate end defer distances on cards. |
The compass |
The
Roberval's balance
Gilles Personne de Roberval (1602 - 1675), professor of mathematics
to the "College de France" in Paris, invented a balance
which bears its name.
The two plates of this balance
rest, on two knives whose edges are turned to the top and are
fixed at two mobile stems, connected between them at their lower
ends by a mobile lever.
This position which does not change the equilibrium conditions,
makes very convenient the use of this balance. |
The Roberval's balance |
The
barometer
The simplest barometer is the
Torricelli's tube who filled with dry mercury in order to not
contain neither gas, nor vapor above mercury.
The pressure measured by the barometer is expressed in millimeter
of mercury.
It makes it possible to meausure altitudes indirectly. The mercury
contained in the tube rises of 1 mm by 10 m rise.
It is very useful for wheather forecasting. |

The barometer |
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