Of his childhood nothing is known. It was some time in his early boyhood days that he went to Amsterdam, where he found employment, it appears at first, in the house of a Holland merchant, and later as a joiner’s apprentice. We can be certain neither of the time when he decided to leave Amsterdam, nor of the circumstances which induced him to visit the island of Hveen, then belonging to Denmark,[2] an event of much significance in his life. We, however, cannot be far wrong in asserting the promptings for this visit to have been his early liking for mathematical, geographical and astronomical studies. On this island he was brought into intimate relations with Tycho Brahe, the famous Danish astronomer, who, in 1576, established here his observatory at the Castle of Uranienburg.[3] For near a quarter of a century, this was one of the most famous centers in all Europe for the study of astronomical science and of its practical applications. Blaeu, let it be noted, was not the first of the young Netherlanders who found his way to Uranienburg that he might receive astronomical instructions from the great master. As early as 1591, Jacob Florent van Langren of Amsterdam sent his son Arnold to the Danish astronomer with a request that he might be allowed to copy the catalogue of the stars which had been located at his observatory, wishing to make use of the same in the new celestial globes which he proposed to construct. This special request, we are informed, was not granted, for Brahe’s records were not yet complete, but young van Langren was given permission to see the large celestial globe which was in the observatory, and on which at the time of the visit 800 stars had been represented.[4] It is stated that Tycho often had as many as ten or twelve boys at his observatory as his assistants. [Illustration: Island of Hveen, showing the location of Uranienburg. From Le Grand Atlas] We have but little direct information concerning Blaeu’s sojourn at Uranienburg. It appears certain that he passed at least two years with Brahe, engaged the while in study and in the construction of mathematical and astronomical instruments. May 21, 1596, the day of the young Hollander’s departure for his native land, Brahe made the following entry in his day-book, which book may be found in the Imperial Library of Vienna, “Abiit domum in Hollandiam, Vilhelmus Batavius cum per integram hyemen his fuisset,” and by Gassendi we are told that Guilielmus Janssonius had been with Tycho for two years, although he does not make it certain that it was for two consecutive years. That the relations between the two distinguished scientists continued to be of the most friendly character long after the date given above is very certain, as not a few of those who in later years in praising Blaeu’s scientific attainments refer to him as “the pupil and longtime friend of Brahe,” yet neither of them appears in his writings to have made more than a passing allusion to their relations.[5]