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PHOTO-TELEGRAPHY 363
important part has now come to be known as Belin's method. In reality this method is very much the same as one, the basis of which was first proposed by Amstutz in 1885, and patented 1891.
The sending apparatus consists essentially of a carbon process photograph prepared with extra thick tissue, so that the picture obtained possesses great relief. Just as in the previously described method, so in this, the cylinder or drum to which this photograph is attached is made to rotate by means of a motor.
A sapphire stylus is pressed against the print, and this stylus is attached to a movable arm having a pivot slightly above the point where the stylus joins it. The arm ends in its lower part with a small platinum wheel. It can readily be seen from the diagram that a very small movement of the stylus would result in a much more considerable one in the case of the wheel. Now, this wheel is so arranged that by the movement of it, caused by the stylus moving over the uneven surface of the picture, it can pass backwards and forwards over a tiny rheostat composed of twenty copper strips carefully insulated from each other. Each of these strips is in connection with a different resistance coil. On account of this arrangement, as the cylinder with the picture revolves, and the platinum wheel is moved, changes of current will be experienced at the receiving station, which can be made use of to form the picture.
A nernst lamp is used to throw a beam of light on to the mirror of an oscillograph, the turning part of which moves in oil. The mirror of this instrument turns about its axis in proportion to the amount of current sent by the transmitter, hence it is able to cast the spot of reflected light more or less to one side of a graduated scale of tints. The light emerging from this tinted scale is converged by a lens, so that it is brought to a focus upon a piece of bromide paper wrapped round the receiving cylinder, which, of