A TALKING FIDDLE.

Star (Christchurch), Issue 16494, 3 August 1921, Page 6

A TALKING FIDDLE.

NEW USES FDR ELECTRICITY. CHEAPER TELEPHONES. A striking application of a new discovery they have made was exhibited at the Institution of Electrical Engineers in London by two young Danish scientists, Mr Alfred Johnsen and Knud Rahbek. This was nothing less than a stringless violin, which was made to talk, and to reproduce musical selections-—Dvorak’s “ Humoresque ” for instance—by a person in a distant room. Tho violin was an ordinary instrument with tho strings taken away. It was clamped high up, in full view of the audience, to a table, and in front of the instrument was placed a rotating cylinder ot agate rubbing against a piece of metal, which was the direct player. When the violinist, a lady, played m the other room, the reproduction of tone, as if ” by magic numbers and persuasive sound” was so perfect and elicited applause so hearty and so long that an encore was given. After that the violin was made to reproduce the human voice, and to the delight of the audience the first part of the speech delivered by the first president of the association, Mr Siemens. on February 28, 1872, came out of the instrument. The discovery, of which these wonderful things were a quite simple application, is also easily understood. It was made during experiments in telephony, and the lecture In which it was described was read last night by Air Johnsen, while Air Rahbek conducted the experiments. It appears that in 1917 Messrs Johnsen and Rahbek discovered that a strong adhesive force was developed when an electric current was applied to two solid bodies, o-ne of them a bad conductor of electricity (certain minerals, for example) and one of them a conducting body (such as a metal disc) resting upon the other. This adhesion was found to he increased in proportion to the area of contact between the two bodies—for instance, by one of them being made to revolve. An attraction equal to several pounds can be obtained between an ordinary thick lithographic stone and a “An metal disc resting on it when an electric current of 440 volts fs applied. Tho current then is of the value of only a few micro-amperes, which is a very weak one. The disc will lift the stone while the current i applied and drop it if the current be interrupted in the same way that an electro-magnet can be lifted by its armature. This experiment, however, cannot be carried out with true insulators such as glass, mica, hard rubber, etc., for then the necessary current cannot flow.

Air Johnsen explained an important difference between this new electrically produced adhesion and 1 that of the common electro-magnet. The armature will attract its magnet from a distance, but in the new experiments the conducting body and the bad conductor must be in close contact. The closer and smoother their surfaces in contact the more the adhesion produced. A j comparatively low current can be em- ! ployed to produce a comparatively big force of adhesion. Tins attraction naturally causes a considerable friction j between the two faces. This is utilised | for technical purposes by using the | badly conducting body in the form of a cylinder which is kept in rotation, and on which a metal band slides. By applying r. suitable electric current the band can be made to adhere firmly to the cylinder, and can be made to con*tract springs and operate various device?-, the whole forming what electrical engineers know as an electrostatic relay. A POCKET TELEPHONE. Clearly, therefore, if a diaphragm in a sound box was made to replace 1 tho cylinder in this contrivance, a pocket telephone could be made, and other alterations would result in a pocket electroscope for testing the strength of currents. The lecturers also showed how tlie discovery could be applied to a wireless telegraph, transmitting wireless messages far more rapidly than at pro sent even up to GQO words per minute and recording them on the paper tape. Other applications oi the new discovery will be an improved telegraphic J receiver, a cheap electric bell device, a I loud-speaking telephone, and important] developments may be expected in connection with wireless telephony and submarine telegraphy. Cheaper operation of telephones waj also promised by the lecturer as a conI sequence of this new telegraphic transmitting leiay.