Brought To You in cooperation with the Musée des Arts et Métiers - Paris.

The aerial telegraph  created by Claude Chappe (1794) is a means of optical communication. The telegraphic network  was made up of a succession of semaphores perched atop towers that were 6 to 12 kilometers apart. The position of the semaphore wings indicated a coded message to be transmitted. Each such position corresponded to a number which directed the receiver to a specific page in a notebook where the message in letters  could  be found.

Animation brought to you in cooperation with the Musée des Arts et Métiers - Paris.

The velocipede (literally "fast foot") uses a chain set with a fixed sprocket on the front wheel: one turn of the pedals is the equivalent of one turn of the driving wheel.

To travel greater distances with each turn of the pedals it is necessary to increase the diameter of the front wheel: the Penny Farthing is an extreme application of this principle.

The bicycle uses a transmission system that involves a chain connecting two sprockets of different sizes, which provides greater distance to be covered with each turn of the pedals.

Animation brought to you in cooperation with the Musée des Arts et Métiers - Paris.

The velocipede (literally "fast foot") uses a chain set with a fixed sprocket on the front wheel: one turn of the pedals is the equivalent of one turn of the driving wheel.

To travel greater distances with each turn of the pedals it is necessary to increase the diameter of the front wheel: the Penny Farthing is an extreme application of this principle.

The bicycle uses a transmission system that involves a chain connecting two sprockets of different sizes, which provides greater distance to be covered with each turn of the pedals.

Counting days is simple. The day/night cycle can be observed everywhere on Earth (except sometimes at the poles).

Counting months is more complicated. Though initially based on the lunar cycle of 29.5 days, one could not round off to 30 because 12 months of 30 days (360 days) do not add up to a year.

All of the difficulties arise from a year that does not contain a whole number of days. The Earth turns around the Sun in 365.2425 days, or practically 365 + ¼ days (365.25). If one ignores this ¼ day, one accumulates discrepancies which can end up placing the month of January in the middle of the summer (after 800 years).

It was in 46 BC, under the reign of Julis Caesar, that the leap year reform was undertaken. For this reason, this calendar  was named the "Julian" calendar.  It was again reformed in 1582 by Pope Gregory XIII.

The digitization of an analogue signal is carried out by taking several samples and translating them into binary code.  The series of codes thus obtained are then regrouped in a digital file. The advantage of such digitization lies in the ability of such file formats to undergo processing  by a computer.  In order to obtain a digitization that corresponds to the original analogue signal one must gain precision. To do this, it is sufficient to increase the sampling frequency and decrease the pace of quantization.

A gear system enables the transmission of motion. In this example, which deals exclusively  with toothed wheels, only rotational motion is dealt with.  The speeds of rotation are a function of the gear ratio (or transmission ratio), which depends solely on the number of teeth on each wheel.

Knowing that the number of teeth is proportional to the wheel's diameter, we can also define the gear ratio as a function of wheel diameters.

A gear system ensures  a transmission without slippage, and with a very high yield. The gear ratio can be greater than 1 (muliplication) or less than 1 (reduction).  Augmentation of the couple  produces a decreased speed, and vice versa.

Contrary to popular opinion, radiation is a natural phenomenon. It was discovered in 1896 by A.H. Becquerel who was studying the fluorescent properties of uranium salts.

We identify 3 distinct types of radioactive decay. Each type of decay liberates a large amount of energy:

1. Alpha radiation: the emission of a helium atom.
2. Beta (+ and -) radiation: the emission of either an electron (beta-) or a positron (beta+).
3. Gamma emission: the liberation of a high-energy photon.

An electric motor converts electrical energy into mechanical energy. The innovation lies in the production of a rotating magnetic field from fixed armature windings with a sinusoidal voltage frequency running through them. Nikola Tesla perfected the uses of this device, resulting in his 1888 invention of the first three-phase electric motor.

Such motors are now everywhere: they are in trains, in washing machines, in factories...

Note that these machines are reversible, that is, that you can also convert mechanical energy into electrical energy. That's what happens in power plants. The machines used in power plants are called generators, or alternators.