An excerpt from the INTRODUCTORY. For the purpose of this book it will be convenient to divide magic into three branches: manual dexterity, mental subtleties and the surprising results produced by a judicious and artistic blending of the second and third branches. There are other branches, to be sure; but they are of little interest to modern students of the magic art. A century ago, and, indeed, as late as Robert-Houdin's day, a general knowledge of the physical sciences was considered necessary to the equipment of the conjurer or magician; and the old writers on magic filled their pages with clumsy experiments in chemistry, physics, mechanics and mathematics. In order to be an original conjurer of the first magnitude, said Robert-Houdin, it is necessary to have more than a speaking acquaintance with the sciences, so as to apply their principles to the invention of illusions and stage tricks. Houdin himself utilized chemistry, optics and physics, while many of his greatest and most successful illusions were based on the then little known science of electricity. Things have changed since Houdin's day, however, and the art he practiced has taken many forward strides toward the goal of perfection.