Dominique F. Arago    1786 - 1853

esperimento di Arago

Arago experiment

Seems thet Arago was the first man to build consciounsly an electromagnet, in september 1820, in the same time he noticed that rhe iron became a magnet only during the flow of current, the effect finished when the current stopped: the basis of Morse telegraph.
Arago had also discovered, in 1824, that a disk of non-magnetic metal had the power of bringing a vibrating magnetic needle suspended over it rapidly to rest; and that on causing the disk to rotate the magnetic needle rotated along with it. When both were quiescent, there was not the slightest measurable attraction or repulsion exerted between the needle and the disk; still when in motion the disk was competent to drag after it, not only a light needle, but a heavy magnet. The question had been probed and investigated with admirable skill both by Arago and Ampere, and Poisson had published a theoretic memoir on the subject; but no cause could be assigned for so extraordinary an action. It had also been examined in this country by two celebrated men, Mr. Babbage and Sir John Herschel; but it still remained a mystery.
Faraday saw mentally the rotating disk, under the operation of the magnet, flooded with his induced currents, and from the known laws of interaction between currents and magnets he hoped to deduce the motion observed by Arago.
About 1850 Arago, J.B.L.Foucault and A.H.Fizeau showed that light travels faster in air than in water. This was the triumph of the wave theory of light.

Animation above: If the current is strong the magnet improves his power and attracts iron with energy.

Animation below: The current of battery changes the coil in a magnet which attracts the magnetic needle.

Those notices come from: Faraday as a Discoverer by John Tyndall


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