HORROCKS, Jeremiah (1619–1041), an astronomer of extraordinary promise blighted by a premature death, was born in 1619 at Toxteth Park, near Liverpool. Of the circumstances of his family little is known, further than that they were poor ; but the register of Emmanuel College, Cambridge, testifies to his entry as sizar, May 18, 1632. Isolated in his scientific tastes, and painfully straitened in means, he pursued amid innumerable difficul ties his purpose of self-education. His university career lasted three years, and on his return to Lancashire he devoted to astronomical observations the brief intervals of leisure snatched from the harassing occupations of a laborious life. In 1636 he met with a congenial spirit in William Crabtree, a draper of Broughton, near Manchester; and encouraged by his advice he exchanged the guidance of Lansberg, a pretentious but inaccurate Belgian astronomer, for that of Kepler. He now set himself to the revision of the Rudolphine Tables (published by Kepler in 1627), and in the progress of his task became convinced that a transit of Venus overlooked by Kepler would nevertheless occur on the 24th of November (O.S.) 1639. He was at this time curate of Hoole, near Preston, having recently taken orders in the Church of England, although, according to the received accouuts, he had not attained the canonical age. The 24th of November falling on a Sunday, his clerical duties threatened fatally to clash with his astronomical observations; he was, however, released just in time to witness the punctual verification of his forecast, and care fully noted the progress of the phenomenon during half an hour before sunset (3.15 to 3.45). This transit of Venus is remarkable as the first ever observed, that of 1631 predicted by Kepler having been invisible in Europe. Notwithstanding the rude character of the apparatus at his disposal, Horrocks was enabled by his observation of it to introduce some important corrections into the elements of the planet s orbit, and to reduce to its exact value the received estimate of its apparent diameter.
After a year spent at Hoole, he returned to Toxteth, and there, on the eve of a long-promised visit to his friend Crabtree, unexpectedly expired, January 3, 1641, in the twenty-second year of his age. It is difficult to over estimate the services which, had his life been prolonged, this singularly gifted youth might have rendered to astrono mical science. To the inventive activity of the discoverer he already united the patient skill of the observer and the practical sagacity of the experimentalist. Before he was twenty he had afforded. a specimen of his powers by an important contribution to the lunar theory. He first brought the revolutions of our satellite within the domain of Kepler s laws, pointing out that her apparent irregu larities could be completely accounted for by supposing her to move in an ellipse with a variable eccentricity and directly rotatory major axis, of which the earth occupied one focus. These precise conditions were afterwards demon strated by Newton to follow necessarily from the law of gravitation.
In his speculations as to the physical cause of tha celestial motions, his mind, though not as yet wholly emancipated from the tyranny of gratuitous assumptions, was working steadily towards the light. He clearly per ceived the significant analogy between terrestrial gravity and the force exerted in the solar system, and used an ingenious experiment to illustrate the composite character of the planetary movements. He also reduced the solar parallax to 14" (less than a quarter of Kepler s estimate), corrected the sun s semi-diameter to 15 45", recommended decimal notation, and was the first to maketidal observations.
Only a remnant of the papers left by Horrocks was preserved by the care of William Crabtree. After his death (which occurred soon after that of his friend), these were, purchased by Dr Worthington, of Cambridge ; and from his hands the treatise Venus in sole visa, passed into those of Hevelius, and was published by him in 1662 with his own observations on a transit of Mercury. The remaining fragments were, under the directions of the Royal Society, reduced by Dr Wallis to a compact form, with the heading Astronomia Kcp- leriana dcfensa ct promote/,, and published with numerous extracts from the letters of Horrocks to Crabtree, in a volume entitled JcremicK Jforroccii Opera Posthuma, London, 1672. A memoir of his life by the Rev. Arundell Blount Whatton, prefixed to a trans lation of the Venus in solo visa, appeared at London in 1859.
HORSE
PART I.—ZOOLOGY AND ANATOMY.
Zoology.
THE horse and its near allies, the several species of asses and zebras, constitute the genus Equus of Linnaeus, a small group of animals of the class Mammalia, so dis tinct in their organization from all other existing members of the class that in many of the older zoological systems they were placed in an order apart, under the name of Solidungula or Monodactyla.
Investigations in comparative anatomy have, however, demonstrated that their structure, at first sight so singular and exceptional, is really but a modification of the same general plan upon which the tupirs and rhinoceroses are formed, and the discovery and restoration of the characters of extinct species, inaugurated by Cuvier during his fruitful researches into the fauna of the Paris basin, continued in various European localities by Kaup, Iliitimeyer, Gervais, Gaudry, Huxley, and others, and recently conducted on a more ample scale in the prolific fossiliferous strata of North America by Leidy, Marsh, and Cope, have revealed numerous intermediate stages through which the existing horses appear to have passed in their modification from a very different ancestral form.
We shall best understand what a horse really is if we first consider its origin and lineage; and this we are in a better position to do than with almost any other animal, as it is one of the few whose history (if the evidence afforded by palaeontology can be relied upon) can be traced back through an almost unbroken chain of links as far as the earliest Tertiary age.
