NO one is better fitted than Dr. du Bois to write a treatise on the magnetic circuit. He is well known for his experimental investigations in magnetism, and abstract magnetic theory is clearer and more comprehensive for his restatement of its main propositions. His German treatise, “Die Magnetische Kreise,” published some five years ago, attracted considerable attention in this country. It gave in reasonable compass an excellent account of magnetic theory, methods of magnetic measurement, and of recent magnetic research, in which Dr. du Bois' own contributions to knowledge formed an important part, not merely on account of their intrinsic value, but of their clear and first-hand and withal modest statement. The Magnetic Circuit. By H. du Bois Translated by E. Atkinson, Ph.D. Pp. xviii + 362. (London: Longmans, Green, and Co., 1896.)