Biography of Andre-Eugene Blondel

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Andre-Eugene Blondel was French physicist known for his invention of the oscillograph and for his development of a system of photometric units of measurement.

Andre-Eugene Blondel was born on August 28, 1863, in Chaumont, France. Blondel became a professor of electrotechnology at the School of Bridges and Highways and the School of Mines in Paris. In 1893 he invented the electromagnetic oscillograph, a device that allowed electrical researchers to observe the intensity of alternating currents. In 1894 he proposed the lumen and other new measurement units for use in photometry, based on the metre and the Violle candle.

His system was endorsed in 1896 by the International Electrical Congress and is still in use with only minor modifications. Blondel also contributed to developments in wireless telegraphy, acoustics, and mechanics and proposed theories for induction motors and for the coupling of alternating-current generators. He received the medal of the Franklin Institute, the Montefiore award and Kelvin Lord award, and the Faraday medal. At last, he became a member of the academy of sciences in 1913.

Oscillograph is the instrument for indicating and recording time-varyingelectrical quantities, such as current and voltage. The two basic forms of the instrument in common use are the electromagnetic oscillograph and the cathode-ray oscillograph; the latter is also known as a cathode-rayoscilloscope, which, strictly speaking, is purely an indicating instrument, while the oscillograph can make permanent records.

The operation of an electromagnetic oscillograph, like the operation of a d’Arsonval galvanometer, depends on the interaction of the field of apermanent magnet and a coil of wire through which an electric current is flowing. Some oscillographs were provided with a pen arm, attached to the coil, that traces an ink record on a moving paper chart. The most common device of this nature was the electrocardiograph, which employs a coil of fine wire with many turns and is used for studying heart action.

The light-beam oscillograph has much less weight to move than does the pen-writing instrument and so responds satisfactorily to higher frequencies, about 500 Hz, or cycles per second, compared with 100 Hz for the pen assembly. It uses a coil to which a small mirror is attached. A beam of light is reflected from the mirror onto a photographic film moving at a constant speed.

The Blondel Oscillograph

In one form of Blondels oscillograph, the vibrating system is a small magnetic needle carrying a mirror, but the principle on which it operates is the same as that of the instrument above described. The oscillograph can be made to exhibit optically the form of the current curve or non-cyclical phenomena, such as the discharge of a condenser.

In this case the large vibrating mirror must be oscillated by a current from an alternator, on the shaft of which is a disk of nonconducting material with brass slips let into it and so arranged with contact brushes that in each period of the alternator a contact is made, charging say a condenser and discharging it through the oscillograph. In this way an optical representation is obtained of the oscillatory discharge of the condenser.

A unit of luminance suggested in 1942 was named blondel after the French physicist A. E. Blondel (1863-1938). One blondel is pi lumens per square meter per steradian.

French postal stamp and a card memorizing Andre-Eugene Blondel.

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