WILLIAM IV  ., landgrave of Hesse (1532-1592), was the son and successor of the landgrave Philip the Magnanimous . He took a leading part in safeguarding the results of the Reformation and was indefatigable in his endeavours to unite the different sections of Protestantism for the sake of effective resistance against the Catholic reaction . His counsels were marred by his reluctance to appeal to arms at the critical moments of action, and by the slenderness of his own resources, but they deserve attention for their broad common sense and spirit of tolerance . As an administrator of his principality he displayed rare energy, issuing numerous ordinances, appointing expert officials, and in particular establishing the finances on a scientific basis . By a law of primogeniture he secured his land against such testamentary divisions as had diminished his own portion of his father's estate . He not only patronized art and science, but continued as ruler the intercourse with scholars which he had cultivated in his youth . William was a pioneer in astronomical research and perhaps owes his most lasting fame to his discoveries in this branch of study . Most of the mechanical contrivances which made Tycho Brahe's instruments so superior to those of his contemporaries were adopted at Cassel about 1584, and from that time the observations made there seem to have been about as accurate as Tycho's; but the resulting longitudes were 6' too great in consequence of the adopted solar parallax of 3' . The principal fruit of the observations was a catalogue of about a thousand stars, the places of which were deter-mined by the methods usually employed in the 16th century, connecting a fundamental star by means of Venus with the sun, and thus finding its longitude and latitude, while other stars could at any time be referred to the fundamental star . It should be noticed that clocks, on which Tycho Brahe depended very little, were used at Cassel for finding the difference of right ascension between Venus and the sun before sunset; Tycho preferred observing the angular distance between the sun and Venus when the latter was visible in the daytime . The Hessian star catalogue was published in Lucius Barettus's Historia coelestis (Augsburg, 1668), and a number of other observations are to be found in Coeli et siderum in eo errantium observationes Hassiacae (Leiden, 1618), edited by Willebrord Snell . R .

Wolf, in his " Astronomische Mittheilungen," No . 45 (Vierteljahrsschrift der naturforschenden Gesellschaft in Zurich, 1878), has given a resume of the manuscripts still preserved at Cassel, which throw much light on the methods adopted in the observations and reductions .