CHRISTIAN, a learned astronomer, born in a village of Denmark in 1562. He was the son of a ploughman, and during his studies had to suffer all the hardships to which his condition exposed him, dividing his time, like the philosopher Cleanthes, between the cultivation of the earth and the lessons he received from the minister of the place. At last, when he was fifteen, he stole away from his family, and went to the college at Wiburg, in which he spent eleven years; and though he was obliged to earn a livelihood, he applied himself to study with such ardour, that amongst other sciences he learned the mathematics in great perfection. He afterwards went to Copenhagen, where the professors of the university of that city soon conceived so high an opinion of him, that they recommended him to the celebrated Tycho Brahe. Longomontanus lived eight years with that celebrated astronomer, and was of great service to him in his observations and calculations. At length, being extremely desirous of obtaining a professor's chair in Denmark, Tycho Brahe consented, though with some reluctance, to deprive himself of his services; gave him a discharge filled with the highest testimonies of esteem; and furnished him with money for the expense of his journey. He obtained a professorship of mathematics in the university of Copenhagen in 1605, and discharged the duty of the office creditably until his death, which happened in 1647. He wrote many learned works, amused himself with endeavouring to square the circle, and pretended that he had actually discovered a mode of doing so; but Dr John Pell, an English mathematician, attacked him warmly on the subject, and proved that he was completely mistaken.