Horrox, Or Horrocks Jeremiah, an English astronomer, born at Toxteth, near Liverpool, about 1616, died there, Jan. 3, 1641. He was matriculated as a sizar at Emmanuel college, Cambridge, July 5, 1632, but left without a degree. Devoting himself to astronomy, he found difficulty in procuring the books and instruments he desired. He was for a time misled and induced to distrust the accuracy of his own observations by their incompatibility with those of Lansberg, but was set right by the study of Tycho Brahe and of Kepler. His telescope, which he did not obtain until May, 1638, cost him only 2s. 6d., but it enabled him to make the first observation ever made of the transit of Venus over the sun's disk, Nov. 24, 1639. The transit in 1631 had been predicted by Kepler, but he had failed to point out that of 1639. The tables of Lansberg indicated the latter, but did not give the time. Horrox supplied the omission by his own calculations, and prepared to watch the phenomenon. At this time he was curate of Hoole, a small village near Preston. The transit, according to his calculation, would take place about 3 o'clock of a Sunday afternoon, but to avoid mistake he began his observations at noon the preceding day.

After careful watching for more than 24 hours, except during the time of divine service, which he would not neglect even in the interest of science, he was rewarded for all his toil and anxiety. This transit was observed only by himself and his friend Crabtree, whom he apprised of the coming event the preceding month. Horrox's account of it, entitled Venus in Sole visa, was printed by Hevelius at the end of his Mercu-rlus in Sole visas (Dantzic, 1662). He remained at Hoole only about six months after this great achievement. The last three months of his life were devoted to a study of the irregularities of the tides, from Which he hoped to obtain a demonstration of the rotation of the earth. He was also the author of the theory that the lunar motions might be represented by supposing an elliptic orbit, if the eccentricity of the ellipse were made to vary, and an oscillatory motion given to the line of apsides. Newton afterward verified his suppositions, and showed that they were consequences of the law of gravitation, but he attributed to Halley what properly belonged to Horrox. The remaining works of Horrox were published by Wallis in 1672, with an exposition of his lunar theory by Flamsteed. A translation of the Venus in Sole visa is appended to the "Memoirs of the Life and Labors of the Rev. Jeremiah Horrox," by Whatton (London, 1859; 2d ed., 1869).