HISTOIRE DE LA TELEVISION
(et de quelques autres médias)
Site édité par André Lange

En 1873, Willoughby Smith, un pionner du câble sous-marin, lance les recherches sur le caractère photo-sensible du sélénium.

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Willoughby SMITH, Letter to Latimer Clark, 4 février 1873.

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"Effect of Light on Selenium during the passage of an Electric Current", Nature, 20 February 1873, p.303.

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Willoughby Smith (né à Great Yarmouth, Angleterre, 6 avril 1828,  mort à Eastbourne, Angleterre, 17 juillet  1891) est un des noms importants du développement de la télégraphie, à laquelle il s'intéresse dès l'age de 20 ans.  En 1848, il rejoint la Gutta-percha Company de Londres, et peu après commence des expériences sur les questions d'isolation, grâce au gutta-percha des fils s en fer et en cuivre. En 1849, son entreprise s'est engagée à fournir 30 miles de fil isolé pour relier Douvres à Calais, et pendant l'année suivante Smith supervise la fabrication et la pose de ce câble. Par la suite, il est constamment engagé dans les questions relatives à la pose de câbles et collabore aux expériences de Charles. 

En 1854 il pose le premier câble méditerranéen, entre Spezzia et la Corse, la Corse et la Sardaigne, et plus tard, entre la Sardaigne et Cona en Algérie. A son retour il a est nommé responsable de la Gutta Percha Works, fondée en 1864. En 1865, il aide à la pose du câble reliant l'Irlande à Terre-Neuve.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Les barres de sélénium utilisées en 1873 par Willoughby Smith (By courtesy of the Institution for Engineering and Technology)

 

 

 

La lettre que Willoughby Smith adresse le 4 février 1873 à Latimer Clark, et que celui s'empresse de faire reproduire dans la revue Nature, marque le début des recherches sur les propriétés photosensibles du sélénium.

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Letter to Latimer Clark

Wharf Road 4 February 1873

My Dear Latimer Clark

    Being desirous of obtaining a more suitable high resistance for use at the Shore Station in connection with my system of testing and signalling during the submersion of long submarine cables, I was induced to experiment with bars of selenium - a known metal of very high resistance. I obtained several bars, varying in length from 5 cm to 10 cm, and of a diameter from 1.0 mm to 1.5 mm. Each bar was hermetically sealed in a glass tube, and a platinum wire projected from each end for the purpose of connection.

    The early experiments did not place the selenium in a very favourable light for the purpose required, for although the resistance was all that could be desired - some of the bars giving 1400 M W absolute - yet there was a great discrepancy in the tests, and seldom did different operators obtain the same result. While investigating the cause of such great differences in the resistance of the bars, it was found that the resistance altered materially according to the intensity of light to which they were subjected. When the bars were fixed in a box with a sliding cover, so as to exclude all light, their resistance was at its highest, and remained very constant, fulfilling ail the conditions necessary to my requirements; but immediately the cover of the box was removed the conductivity increased from 15 to 100 per cent, according to the intensity of the light falling on the bar. Merely intercepting the light by passing the hand before an ordinary gas-burner, placed several feet from the bar, increased the resistance from 15 to 20 per cent. If the light be intercepted by glass of various colours, the resistance varies according to the amount of light passing through the glass.

    To ensure that the temperature was in no way affecting the experiments, one of the bars was placed in a trough of water so that there was about an inch of water for the light to pass through, but the results were the same; and when a strong light from the ignition of a narrow band of magnesium was held about 9 in above the water the resistance immediately fell more than two-thirds, returning to its normal condition immediately the light was extinguished.

    I am sorry that I shall not be able to attend the meeting of the Society of Telegraph Engineers tomorrow evening. If, however, you think this communication of sufficient interest, perhaps you will bring it before the meeting. I hope before the close of the session that I shall have an opportunity of bringing the subject more fully before the Society in the shape of a paper, when I shall be better able to give them full particulars of the results of the experiments which we have made during the last nine months.

I remain

Yours faithfully

Willoughby Smith

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La nouvelle de la découverte se répand très vite. En France; un article "Effets de la la lumière sur le sélénium" est publié dans La Nature en 1873 (p.218).

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Smith développera sa découverte dans une brochure publiée en 1877, Selenium : its electrical qualities, and the effect of light thereon : being a paper read before the Society of Telegraph Engineers, 28th November, 1877.

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Il continuera par la suite ses travaux sur la télégraphie sous-marine et publiera ses mémoires, dans lesquelles sa découverte n'occupe que deux paragraphes The Rise and Extension of Submarine Telegraphy, J. S. Virtue & Co.: London, 1891.

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A sa mort, survenue en 1891, il était considéré comme un des pionniers de la vision à distance par l'électricité, comme en atteste la notice nécrologique parue dans The Watchmaker & jeweller, silversmith & optician 'Nov. 1, 1891)

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