Hoek, Martinus

(b. The Hague, Netherlands, 13 December 1834; d. Utrecht, Netherlands, 3 September 1873)

astronomy.

Hoek is known chiefly for his discovery that several comets move in the same orbit (“comet groups”) and for his investigation of optical phenomena in moving bodies.

He was the son of Andries Hoet, a surgeon in The Hague, and Johanna Maria de Wit. He married a Miss G. A. Brouwer. He studied astronomy at the University of Leiden under F. Kaiser, becoming in 1856 observer at the Leiden observatory and in 1857 extraordinary professor of astronomy at the University of Utrecht. Because of bad health, which compelled him to give up his observational work, he turned to theoretical astronomy. He advised the Netherlands Shipping Company about chronometers, compasses, methods of position finding. Following the cholera epidemics of 1854–1866 he published (1867) extensive mortality tables concerning the Utrecht population.

Hoek’s most important discovery (1865–1868) was that of so-called comet groups following the same orbit. Altogether he found thirty-three comets to belong to six groups. Although he erroneously believed comets to come from outside the solar system, he was right in assuming that they sometimes subdivide by fragmentation and that it is thus that the existence of groups must be explained.

Hoek also investigated optical phenomena in moving bodies (1861–1869). Fresnel had suggested, and Fizeau had found through experimentation (1851), that in an object moving with a velocity υ the “ether” is carried along with a velocity

Where n is the index of refraction. By a modified setup Hoek (1868) reduced this experiment to a zero-method and confirmed the value of the convection coefficient k with a much higher precision (1.3 percent). In the theory of relativity this result is explained, without any “ether,” by simple application of the velocity-addition theorem.

In Hoek’s second experiment (1869), a slit is viewed through a long, horizontal column of water. As the image appears to be independent of the azimuth towards which the apparatus is oriented, with respect to the motion of the earth, Fresnel’s convection factor was confirmed. Together with Oudemans, Hoek also showed that for a given substance the refractive power (n² – 1)/d is not a constant (1864).

BIBLIOGRAPHY

I. Original Works. A bibliography of Hoek’s early publications (1856–1859) is found in Annalen der Sternwarte in Leiden, 1 (1868), 38. See also “On the Comets of 1677 and 1683; 1860 III, 1863 I, and 1863 VI,” in Monthly Notices of the Royal Astronomical Society, 26 (1865), 1–13; “Additions to the Investigations on Cometary Systems,” ibid. (1866), 204–208; “De l’influence des mouvementts de la terre sur les phénomènes fondamentaux de l’optique dont se sert l’astronomie,” in Recherches astronomiques de l’Observatoire d’Utrecht, 1 (1861), 1–68; “Détermination de la vitesse avec laquelle est entrainé un rayon lumineux traversant un milieu en mouvement,” in verslagen der Koniglijke Akademie van Wetenschappen te Amsterdam, 2nd ser., 2 (1868), 189–194, and 3 (1869), 306–313. A slightly abridged text of this is found in Astronomische Nachrichten, 70 (1867), 193–198, and 73 (1869), 193–200; “Recherches sur la quantité d’éther contenue dans les liquides,” in Recherches astronomiques de l’Observatoire d’Utrecht, 2 (1864), 1–71, written with A. C. Oudemans.

II. Secondary Literature. Some biographical details and references are found in P. C. Molhuysen and P. J. Blok, Nieuw Nederlandsch Biografisch Woordenboek, I (Leiden, 1911), 1118–1119. See also the Utrechtsche Studenten Almanak (1874).

M. G. J. Minnaert