MOLL, GERARD

(b. Amsterdam, Netherlands, 18 January 1785; d. Amsterdam, 17 January 1838)

astronomy, physics.

Moll had an enthusiastic interest in many of the physical sciences of his day. His contributions ranged from observing a transit of Mercury to determining the speed of sound.

Moll’s father, a well-to-do businessman, was also named Gerard; his mother was the former Anna Diersen. Although destined for a commercial career, Moll met and talked to sea captains while serving his apprenticeship in Amsterdam, and became intrigued with the art of celestial navigation—to such an extent that he decided to change to astronomy as his life’s work.

Moll studied at the University of Amsterdam, receiving his Ph.D. in 1809, and then continued his studies for some months in Paris. Returning to Holland in 1812, he was appointed director of the observatory in Utrecht. When that university was reorganized in 1815, Moll became professor of physics as well, and continued in both these positions until his death.

With little financial support and a crumbling observatory building, Moll contributed to astronomy rather more by personal contacts with scientists in other countries—especially in Great Britain—than by observing the heavens. His main astronomical accomplishment seems to have been his observation of the transit of Mercury of 5 May 1832.

In physics Moll made several contributions. With Albert van Beek he measured the speed of sound; an artillery battalion was placed at the experimenters’ disposal, cannon were fired simultaneously—at night —from hills about nine miles apart, and the interval between light flash and sound was recorded at either end and then averaged. The value obtained was 332.05 m./sec. (the currently accepted value is 331.45).

Moll also extended the pioneering observations of H. C. Oersted, published in 1820, on the magnetic field that surrounds a wire carrying an electric current. He also investigated the lifting capacities of the electromagnets based on this phenomenon.

In recognition of his services on a commission dealing with weights and measures, the Kingdom of the Netherlands in 1815 appointed Moll chevalier of the Order of the Belgian Lion. In 1835 the University of Edinburgh gave him an honorary LL.D., and in 1836 the University of Dublin followed suit. Moll was buried beside his mother in Amerongen, some fifteen miles east of Utrecht.

BIBLIOGRAPHY

I. Original Works. The experimental work referred to above is described in “An Account of Experiments on the Velocity of Sound, Made in Holland,” in Philosophical Transactions of the Royal Society, 114 (1824), 425–456, written with A. van Beek; Electro-magnetische Proeven (Amsterdam, 1830); “Ueber die Bildung künstlicher Magneto mittelst der Voltaschen Kette,” in Annalen der Physik und Chemie, 2nd ser., 29 (1833), 468–479; and “On the Transit of Mercury of May 5, 1832,” in Memoirs of the Royal Astronomical Society, 6 (1833), 111–117.

A list of fifty articles by Moll appears in the Royal Society Catalogue of Scientific Papers, IV, 433–434. There is some duplication of subject matter, as Moll’s work tended to appear simultaneously in at least two countries.

II. Secondary Literature. An unsigned obituary of Moll appeared in Annual Register for 1838 (London, 1839), app., p. 198. A more extensive notice, by A. Quetelet, in Annuaire de l’ Académie des sciences, des lettres, et des beaux-arts de Belgique, 5 (1839), 63–79, refers to other sources of biographical information in Dutch and Latin.

Note: The so-called Moll’s thermopile was invented by Willem Jan Henri Moll in 1913.

Sally H. Dieke