Etymologically speaking, the word metamorphosis comes from the Greek  “meta-morphosis”, which referred to any change of form, or transformation.

This word applies   perfectly to the fascinating transformation undergone by certain animals in order to pass from their larval to their adult stage.

This animation illustrates the principal stages in the metamorphosis of a butterfly – the Machaon.

An electrical circuit consists of :

• At least two components (also called dipoles because they have two poles) one of which is the generator (also referred to as the source).
• Conducting wires that connect the components to form a closed loop that enables current to flow.

Numerous forms of transpoort operate using electrical energy. Regardless of the dipole used, an electric motor is connected to the generator (not shown in the photos) by two conducting wires.

The electric power available at the terminals of a dipole is equal to the product of the current (I, in amperes, or "amps") and the voltage (E, for "electromotive force", in volts).

Remark: The colors chosen are not the conventional ones. The voltage and the current  could be direct or alternating.

Brought to you in cooperation with the Musée des Arts et Metiers - Paris.

A gear system is one involved in the transmission of motion. The two toothed wheels  assure a driving force without slippage.  In these four systems,  the driving wheel (at top) turns at a constant speed.

• First case: the "Maltese Cross " system transforms the contiunuous rotation into discontinuous motion: this is a turn counter.
• Other cases: the variable speed of the lower wheel is determined by the wheel's geometry.

Animation produced in collaboration with the Musée des Arts et Metiers - Paris.

The arithmetic machine created by Blaise Pascale (1623-1662) - the Pascaline - was one of the first mechanical calculating devices (first model 1642). It's a calculating machine because the carrying over across places occurs automatically.

It enables one to directly add and subtract.  It is also possible to multiply and divide using successive additions and subtractions.

"Consul - the educated monkey" was originally produced from 1916 - 1918 by the Educational Novelty Co, Ohio USA.

This is an early example of a mathematical toy. When each of the monkey's feet are moved to point at two numbers, the hands move to indicate the product.

Brought to you in cooperation with the Musée des Arts et Metiers - Paris.

The principle of operation of all mechanical clocks rests  on the combination of the following three functions:

• A source of energy that can produce rotary motion (here, a driving weight)
• A regulator:  A pendulum measures time precisely and without variations. The escapement system , linked to the pendulum,  enables control of the rate of energy release.
• A display:  graduations and needles ("hands") provide access to the measured information.

Escapements generally use an anchor, as shown in this animation. For small angles (<5°) of oscillation of the pendulum, one approaches the condition of isochronism:  the pendulum's period depends practically exclusively on local gravitational conditions and the length of the pendulum (bit not on either the mass of the pendulum or the amplitudes of its oscillations).  For example, in Paris, a meter long pendulum has a period of two seconds. Lengthening the pendulum increases its period of oscillation.

We all know that it is the Earth that moves around the Sun. But for us, on Earth, it is the Sun that seems to move around the Earth, from East to West. This is what is called the apparent path of the Sun. It varies from season to season. It varies even more when the place of observation is at high latitude.

Remark:

• This animation illustrates the apparent path of the Sun for an observer in the Northern Hemisphere, between 40° and 50° of latitude. Someone living in the Southern Hemisphere sees the Sun toward the North, but still moving from East to West.
• Hours are expressed in Solar Time: noon (12:00) is the moment at which the Sun attains its maximum elevation.

The Earth is tilted on its orbit. This causes an unequal amount of sunshine to fall in different parts of the planet during the course of a year, and this is responsible for the seasons. You can use this animation  to illustrate the  variations in the length of daylight,  and the seasons,  in the northern hemisphere.

The circles represented are:

1. Arctic circle (66°N)
2. 45°N latitude (Seattle, Toronto, Milan)
3. Equator
4. Antarctic circle (66°S)

The animation is not drawn to scale for either sizes or distances. Nor are the relative speeds of rotation and revolution accurately represented.

An atmosphere is a layer of gas that surrounds a planet.

The Earth's atmosphere is divided by scientists into  5  theoretical layers:

• The Troposphere contains   80% of the 5 trillion tons of air!  In direct contact with and heated by the ground, this layer of air is where the important thermal exchanges responsible for meteorological  phenomena take place.
• In the Stratosphere, the temperature gets higher as altitude increases.  This temperature inversion acts as a limit for clouds. It is here that we fiind the Ozone Layer that filters out a large part of the ultraviolet radiation coming from the Sun.
• In the Mesosphere, the temperature once again begins to drop.
• Those rare particles still present in the Thermosphere interact with solar radiation.  In absorbing this energy, they increase in temperature and ionize. This is the ionosphere. This part of the Thermosphere has important electromagnetic properties.  The International Space Station (ISS) is in orbit in the thermosphere, beyond the ionosphere.
• Partcles are so rare in the Exosphere that the probability of collisions among them is negligible. Some even escape the gravitational attraction of the Earth. Although the boundary is not clearly defined, the exosphere marks the beinning of outer space.  The majority of satellites are   orbiting in the exosphere, at altitudes between 800 km and 36,000 km.

A loudspeaker is a system that transforms an electric signal into a mechanical signal. At the heart of this system we find a coil made of conducting wire, carrying an electrical current, which moves  under the effects of magnetic forces. A flexible membrane (or diaphragm), attached to the coil, acts like a piston that pushes the surrounding air. This animation has been slowed down many thousands of times -- audible signals lie between 20 and 20,000 Hz.