Two principal subjects seem to have formed the groundwork of his teaching at this period.  The first was the doctrine of the Thirty Divine Attributes, based on S. Thomas of Aquino.  The second was Lully’s Art of Memory and Classification of the Sciences.  This twofold material he worked up into a single treatise, called De Umbris Idearum, which he published in 1582 at Paris, and which contains the germ of all his leading speculations.  Bruno’s metaphysics attracted less attention than his professed Art of Memory.  In an age credulous of occult science, when men believed that power over nature was being won by alchemy and magic, there was no difficulty in persuading people that knowledge might be communicated in its essence, and that the faculties of the mind could be indefinitely extended, without a toilsome course of study.  Whether Bruno lent himself wittingly to any imposture in his exposition of mnemonics, cannot be asserted.  But it is certain that the public were led to expect from his method more than it could give.

The fame of his Art of Memory reached the king’s ears; and Henri III. sent for him.  ’The king, says Bruno, ’had me called one day, being desirous to know whether the memory I possessed and professed, was natural or the result of magic art.  I gave him satisfaction; by my explanations and by demonstrations to his own experience, convincing him that it was not an affair of magic but of science.’  Henri, who might have been disappointed by this result, was taken with his teacher, and appointed him Reader Extraordinary—­a post that did not oblige Bruno to hear Mass.  The Ordinary Readers at Paris had to conform to the usages of the Catholic Church.  On his side, Bruno appears to have conceived high admiration for the king’s ability.  In the Cena della Ceneri and the Spaccio della Bestia Trionfante, composed and published after he had left France, he paid him compliments in terms of hyperbolical laudation.  It would be vain to comment on these facts.  No one conversant with French society at that epoch could have been ignorant of Henri’s character and vicious life.  No one could have pretended that his employment of the kingdom’s wealth to enrich unworthy favorites was anything but dishonorable, or have maintained that his flagrant effeminacy was beneficial to society.  The fantastic superstition which the king indulged alternately with sensual extravagances, must have been odious to one whose spiritual mistress was divine Sophia, and whose religion was an adoration of the intellect for the One Cause.  But Henri had one quality which seemed of supreme excellence to Bruno.  He appreciated speculation and encouraged men of learning.  A man so enthusiastic as our philosopher may have thought that his own teaching could expel that Beast Triumphant of the vices from a royal heart tainted by bad education in a corrupt Court.  Bruno, moreover, it must be remembered, remained curiously inappreciative of the revolution effected in humanity by Christian morals.  Much that is repulsive to us in the manners of the Valois, may have been indifferent to him.