Euler[10] was a believer in God, downright and straightforward. The following story is told by Thiebault,[11] in his _Souvenirs de vingt ans de sejour a Berlin_,[12] published in his old age, about 1804. This volume was fully received as trustworthy; and Marshall Mollendorff[13] told the Duc de Bassano[14] in 1807 that it was the most veracious of books written by the most honest of men. Thiebault says that he has no personal knowledge of the truth of the story, but {4} that it was believed throughout the whole of the north of Europe. Diderot[15] paid a visit to the Russian Court at the invitation of the Empress. He conversed very freely, and gave the younger members of the Court circle a good deal of lively atheism. The Empress was much amused, but some of her councillors suggested that it might be desirable to check these expositions of doctrine. The Empress did not like to put a direct muzzle on her guest's tongue, so the following plot was contrived. Diderot was informed that a learned mathematician was in possession of an algebraical demonstration of the existence of God, and would give it him before all the Court, if he desired to hear it. Diderot gladly consented: though the name of the mathematician is not given, it was Euler. He advanced towards Diderot, and said gravely, and in a tone of perfect conviction: _Monsieur,_ (a + b^{n}) / n = x, _donc Dieu existe; repondez!_[16] Diderot, to whom algebra was Hebrew, was embarrassed and disconcerted; while peals of laughter rose on all sides. He asked permission to return to France at once, which was granted. ROTATION OF THE MOON. An examination of the Astronomical doctrine of the Moon's rotation. By J. L.[17] Edinburgh, 1847, 8vo. A systematic attack of the character afterwards made with less skill and more notice by Mr. Jellinger Symons.