In the warm countries ticks (Ixodes) are troublesome pests. See PARASITES.
ARAGO, Dominique Francois, a celebrated French astronomer: b. in Estagel 1786; d. in Paris, 2 Oct. 1853. After studying at the Polytechnic School at Paris he was ap pointed secretary of the Bureau des Longitudes, and in 1806 was associated with the Biot and in completing the measurements of Delambre and Mechain to obtain an arc pf the meridian which was to serve as the basis of a new metrical system. In 1809 he was elected to fill the seat left vacant by the death of Lalande in the Academy of Sciences, and at the same time he was appointed a professor of the Polytechnic School. In 1811 he communicated to the Insti tute a paper on a particular modification which the luminous rays experience in their passage through certain transparent bodies, thus paving the way for some of the most brilliant discov eries made in optical science since the days of Newton. In 1812 he began a series of lectures on astronomy, which created an immense sensa tion. With Gay-Lussac he established in 1816
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His discovery of the magnetic properties of sub stances devoid of iron procured him the Copley medal of the Royal Society of London in 1825, and a further consideration of the same sub ject led to the equally remarkable discovery of the production of magnetism by electricity. In 1830, on the death of Fourier, Arago succeeded him as perpetual secretary to the Academy of Sciences, becoming in the same year director of the Observatory. After the expulsion of the Bourbons Arago was elected to the Cham ber of Deputies as representative of the Pyrenees-Orientales, taking his place on the extreme left, and proving a ready and effective speaker. The revolution of 1848 brought him still more prominently upon the scene, first as Minister of War and Marine in the provisional government, and then as a member of the executive committee of the National Assem bly. His