Theodose-Achille-Louis, Comte du Moncel, was born at Paris on March 6, 1821. His father was a peer of France, one of the old nobility, and a General of Engineers. He possessed a model farm near Cherbourg, and had set his heart on training his son to carry on this pet project; but young Du Moncel, under the combined influence of a desire for travel, a love of archaeology, and a rare talent for drawing, went off to Greece, and filled his portfolio with views of the Parthenon and many other pictures of that classic region. His father avenged himself by declining to send him any money; but the artist sold his sketches and relied solely on his pencil. On returning to Paris he supported himself by his art, but at the same time gratified his taste for science in a discursive manner. A beautiful and accomplished lady of the Court, Mademoiselle Camille Clementine Adelaide Bachasson de Montalivet, belonging to a noble and distinguished family, had plighted her troth with him, and, as we have been told, descended one day from her carriage, and wedded the man of her heart, in the humble room of a flat not far from the Grand Opera House. They were a devoted pair, and Madame du Moncel played the double part of a faithful help-meet, and inspiring genius. Heart and soul she encouraged her husband to distinguish himself by his talents and energy, and even assisted him in his labours.

About 1852 he began to occupy himself almost exclusively with electrical science. His most conspicuous discovery is that pressure diminishes the resistance of contact between two conductors, a fact which Clerac in 1866 utilised in the construction of a variable resistance from carbon, such as plumbage, by compressing it with an adjustable screw. It is also the foundation of the carbon transmitter of Edison, and the more delicate microphone of Professor Hughes. But Du Moncel is best known as an author and journalist. His 'Expose des applications de l'electricite' published in 1856 ET SEQ., and his 'Traite pratique de Telegraphie,' not to mention his later books on recent marvels, such as the telephone, microphone, phonograph, and electric light, are standard works of reference. In the compilation of these his admirable wife assisted him as a literary amanuensis, for she had acquired a considerable knowledge of electricity.

In 1866 he was created an officer of the Legion of Honour, and he became a member of numerous learned societies. For some time he was an adviser of the French telegraph administration, but resigned the post in 1873. The following year he was elected a Member of the Academy of Sciences, Paris. In 1879, he became editor of a new electrical journal established at Paris under the title of 'La Lumiere Electrique,' and held the position until his death, which happened at Paris after a few days' illness on February 16, 1884. His devoted wife was recovering from a long illness which had caused her affectionate husband much anxiety, and probably affected his health. She did not long survive him, but died on February 4, 1887, at Mentone in her fifty-fifth year. Count du Moncel was an indefatigable worker, who, instead of abandoning himself to idleness and pleasure like many of his order, believed it his duty to be active and useful in his own day, as his ancestors had been in the past.