Daniel Kirkwood, an American mathematician, born in Harford co., Md., Sept. 27, 1814. He was mathematical tutor in the academy of York co., Pa., from 1838 to 1843, when he became principal of the Lancaster high school, and resigned in 1848 to accept a position in the Pottsville academy. In 1849 he communicated to the American philosophical society, at Philadelphia, and to the American association for the advancement of science, at Cambridge, Mass., his then recently discovered analogy between the periods of rotation of the primary planets. In 1851 he became professor of mathematics, and in 1854 president, of Delaware college, resigning in 185(5 to take the chair of mathematics in Indiana university at Bloomington. He has been an earnest advocate of the nebular hypothesis. His paper in the monthly notices of the royal astronomical society, vol. xxix., " On the Nebular Hypothesis, and the Approximate Commensurability of the Planetary Periods," applies the theory of Laplace to explain the existence of gaps and chasms in the zone of minor planets between Mars and Jupiter, and assigns a physical cause for the hiatus in Saturn's ring.

Noticing this paper, Mr. R. A. Proctor says of Prof. Kirkwood's researches: "I believe they will inaugurate new and important processes of thought, by means of which the noble and hitherto intractable problems connected with the formation of the solar system may be found capable of solution." Prof. Kirkwood has also published " Comets and Meteors: their Phenomena in all Ages, and their Mutual Relations, and the Theory of their Origin " (Philadelphia, 1873). He received the degree of LL. D. from the university of Pennsylvania in 1852.