On his return to Prague in 1601, he was presented by Tycho to the Emperor, who conferred upon him the title of Imperial Mathematician, on the condition that he would assist Tycho in his calculations. This connexion was peculiarly valuable to Kepler, as the observations of his colleague were the only ones made in the world which could enable him to carry on his own theoretical inquiries. These two astronomers now undertook to compute, from Tycho's observations, a new set of astronomical tables, to be called the Rudolphine Tables, in honour of the Emperor. This scheme flattered the vanity of their master, and he pledged himself to pay all the expenses of the work. Longomontanus, Tycho's principal assistant, took upon himself the labour of arranging and discussing the observations on the stars, while Kepler devoted himself to the more congenial task of examining those on the planet Mars, with which Tycho was at that time particularly occupied. The appointment of Longomontanus to a professorship in Denmark, and the death of Tycho in October 1601, put a stop to these important schemes. Kepler succeeded Tycho as principal mathematician to the Emperor, and was provided with a handsome salary, which was partly charged on the imperial treasury, and partly on the States of Silesia, and the first instalment of which was to be paid in March 1602. The generosity of the Emperor did not fail to excite the jealousy of ignorant individuals, who were not aware of the value of science to the state; but the increasing fame of Kepler, and the valuable works which he published, soon silenced their opposition.