The truth as to the merits of the mediaeval Arab writers on science will not appear until a more thorough examination of their works has been made. Dr Schoy, who has already done a good deal in this direction for Arab mathematics, points out in the preface to his translation what can be gathered from this modest little treatise. Ibn al-Haytham, the author, a well-known mathematician and scientist, many of whose works have been preserved, lived at Cairo in the beginning of the eleventh century of our era. In discussing the nature of the spots on the moon, he examines a number of erroneous theories prevalent and refutes them one by one; he then arrives at conclusions quite near those of science of today, and one may well marvel at what he accomplishes with no means other than those of his own unaided vision. He achieves his discovery not only by careful reasoning, but as it seems also by much accurate personal observation. Students of the history of science should read the book.

Any such an array of monographs, each based upon a study of original manuscripts, would be impressive merely on the score of number, but in this case the product is even more so in respect to scholarship. To give, as in his article on the "Geography of the Moslems of the Middle Ages," the first translation of the method of Ibn Yûnus for finding longitude by observing solar eclipses; to show by means of a translation from Sibt al-Mâridinî that the Egyptians of the Middle Ages were the first to use a sundial directed towards the world pole; to be the first to give us a translation of Ibn Ali al-Hasan's work on the interpretation of the irregularities of the lunar surface; and to make more clearly known, by accurate translations, the nature of the umbra recta and umbra versa in the leading Arabic works on trigonometry, - these (to mention only a few instances) are gratifying promises of future contributions of great moment.

The day after reading the proof of the above article word was received of the sudden death of Dr Schoy, on December 6, 1925, as the result of an apoplectic stroke. He was forty-eight years of age and had not been in good health for some time, as his latest letter to me showed. His funeral took place at Frankfurt am Main on December 9. Thus passes away a brilliant scholar and an indefatigable worker. Not until he was about forty years of age did he find his real life work, but in the few years that followed he made remarkable progress.

The premature death of our friend Carl Schoy was peculiarly tragical. Very few persons will ever be qualified to advance our knowledge of Muslim mathematics, for such qualification involves a very rare combination of qualities. One needs to be a mathematician and astronomer, have a good knowledge of Arabic or Persian or both, historical sense, palaeographical experience, and be ready, as for any worthwhile achievement, to spend one's time and energy without counting. Schoy combined all these qualities, that is, he had gradually combined them at the cost of long studies and in spite of ill health and increasing discomfort. His first study on Arabic astronomy appeared in 1911 and during the following fifteen years he had produced a good many valuable papers. It is hardly necessary to insist upon this, as many of these papers appeared in Isis, both before and after his death. He left behind a large number of manuscripts, some ready for publication, others in various stages of completion. We all felt that Schoy, if he had been granted to live ten or twenty years longer, would have increased considerably our understanding of oriental mathematics and astronomy. Valuable as his early studies were, his knowledge and experience were continually increasing, and we felt that the very best that he could give us was still to come. But it was not to be!

With the death of Carl Schoy on December 6, 1925, scholarship in the field of history of exact science suffered a severe and irreparable loss. In his short life time, Schoy had done much very valuable work in uncovering the buried treasures of Arabian mathematics, including in particular many on astronomical and geographical subjects. In his earlier years handicapped by poverty, and later by an insidious and incurable disease, Schoy's career compels our admiration for his never-failing courage and indomitable will, no less than for his scientific achievements. The book under review was finished and prepared for the press by the author in 1924, but was not published until after his death, when it was seen through the press by J Ruska and H Wieleitner. Although it is the most extensive published work of the author, he had designed it to be only a small section in a history of Arabian mathematics which he was planning to write. ... This book is a very valuable addition to the primary sources of information about Arabian mathematics, and emphasizes the greatness of the loss which its author's premature death has caused.