Photophone

As photophone or Photo Phone (Greek ) is called an Alexander Graham Bell and Charles Sumner Tainter in 1880 invented an instrument for audible transmission of human speech in greater distance with the help of a bundle of light rays. It is based on the behavior of selenium to light. It is a form of radiophony and a precursor of the optical radio relay.

Operation

Selenium has the property that its conducting power for electricity varies with the intensity of the lighting, and you can make a light-sensitive selenium cell, if you rolled two fine brass wires in the form of flat spirals on a mica sheet shall be submitted, that they do not touch each other, and it then becomes coated with selenium.

Through a lens now a sunlight falls on a mirror b of thin glass or mica, which comes through in a horn against his back spoken words into corresponding vibrations and these vibrations also conveys the light beams. The reflected by the mirror light rays pass through the lens c in the parabolic mirror e the receiving station in the focal point of the selenium cell d is what is on the phone g in f emanating from the galvanic battery power.

In this device, therefore, the light beam of the actual vehicle of sound, while the battery and the selenium cell form only parts of the receiving apparatus. Also, electrical, Drummond cal and even the light of a kerosene lamp are suitable for operation of the Photophons.

You can also completely waive the selenium, and it is sufficient to let the of the vibrating through spoken words mirror reflected light to a thin hard rubber disk in an ear trumpet fall. In addition to hard rubber and many other body for from a vibrating mirror reflected light beam are sensitive; least Bell found only in the coal and in the glass two substances which appeared insensitive.

Pros and Cons

The photophone requires no line and it has a significant advantage over the phone while it is on the other hand depends on the nature of the atmosphere, which does not always allow the posting of light rays on longer distances.