Here is the best mini-history of pre-Mesmerism on the entire Internet. It is an extract from an 1850 tome by J. S. Grimes whose full title is: Etherology and the phreno-philosophy of Mesmerism and magic eloquence; including a new philosophy of sleep and of consciousness, with a review of the pretensions of phreno-magnetism, electro-biology, etc. By J. Stanley Grimes, Counsellor at Law, Formerly President of the Western Phrenological Society, Professor of Medical Jurisprudence in the Castleton Medical College, and Author of “A New System of Phrenology.” All the known phenomena of the universe may be referred to three general principles, viz., Matter, Motion, and Consciousness. Revised and Edited by W. G. Le Duc.

This is from the footnote starting on page 42:

Van Helmont

[No author of the 16th and 17th centuries] appears to have so fully anticipated the discovery of mesmerism as Van Helmont.

He defines magnetism as “that occult influence, which bodies exert over each other at a distance, whether by attraction or by impulsion.” The medium or vehicle of this influence he designates by the name of the magnale magnum, which he seems to consider as a universal fluid pervading all nature. It is not, he continues, a corporeal substance, capable of being condensed, measured, or weighed; but an ethereal, pure, vital spirit, or essence, which penetrates all bodies, and acts upon the mass of the universe. With regard to the human frame, he conceives that the seat of the magnetic force is in the blood, and that it is called forth and directed by the will. Van Helmont occasionally gives to this influence the epithets of ecstatic and magical, using the latter word in its more favorable signification.

In the same treatise,the author proceeds to say that there resides in man a peculiar energy, which enables him, by the mere force of his will and imagination, to act at a distance, and to impress a virtue, to exercise an influence upon a very remote object. This power, he admits, is incomprehensible; but there are other powers and agents in nature, which we are equally incapable of comprehending—such as the power of volition over the corporeal organs. The union of the soul and the body, too, and their reciprocal influence upon each other, depend upon causes which we are unable to discover.

But one of the most remarkable passages in this treatise is that in which the author explains the conditions necessary to the success of the magnetic treatment. “We have already observed,” says he, “that all magical power lies dormant in man, and that it requires to be excited. This is invariably the case, if the subject upon whom we wish to operate is not in the most favorable disposition; if his internal imagination does not abandon itself entirely to the impression which we wish to produce upon him; or if he, towards whom the action is directed, possesses more energy than he who operates. But when the patient is well disposed, or weak, he readily yields to the magnetic influence of him who operates upon him through the medium of his imagination. In order to operate powerfully, it is necessary to employ some medium; but this medium is nothing, unless accompanied by the internal action.” All this—at least in its essential points—is quite coincident with the modern doctrine of animal magnetism, introduced by Mesmer, and established by the numerous experiments and observations of his successors.

Van Helmont, and indeed most of the early writers on the subject of magnetism, ascribed a vast and mysterious influence to the power of energetic and concentrated volition.

The will, according to Van Helmont, is the first of powers. It was by the will of the Almighty that the universe was created; it was by volition that motion was originally impressed upon all objects; it is the will existing in man which is the principle of all his actions. Volition belongs to all spiritual beings; it is the more active and powerful in them in proportion as they are disengaged from matter; and the energy with, which it operates without the assistance of organs, is the essential characteristic of pure spirits. He also remarks, that those who exert the magnetic influence operate more or less powerfully, according to the energy of the will; and that the effects of their operation may be impeded by the resistance of that which is operated upon.

It is quite evident, indeed, from the whole works of Van Helmont, that he was not only perfectly well acquainted with the magnetic influence, but that he made use of it professionally, and placed great confidence in its effects. He himself, indeed,informs us, that when the plague was raging in the town of Brussels, he thought it his duty to seize the opportunity of instructing himself, and of being useful to others. He accordingly offered his services to attend the sick; neither the fatigue, nor the fear of infection, could abate his zeal, or extinguish his charity. “Perceiving,” says he, “that most of the physicians deserted the sick, I devoted myself to their service, and God preserved me from the contagion. All, when they saw me, seemed to be refreshed with hope and joy; whilst I, supported by faith and confidence, persuaded myself that God would at length confer upon me the science of an adept.”

There appeared in England, about the middle of the seventeenth century, three persons, who seem to have possessed considerable mesmeric power, which they employed, however, only for the cure of diseases. These were a gardener named Levret, an Irish gentleman, Valentine Greatrakes, and a Dr. Streper. Their method of cure was altogether by manipulations, and their success was wonderful, and indeed almost incredible.

In the course of the next century, there appeared, in Germany, a still more extraordinary character than either of the three who performed such wonders in England. This was John Joseph Gassner, who was born at Bratz, in Suabia, in 1727, and who became a Catholic priest. His curative powers were most amazing, especially in spasmodic and epileptic complaints, and were authenticated in the most ample and irrefragable manner, by persons of high rank and irreproachable character.

But it was reserved for Mesmer, one of the most remarkable men on record, to deduce and form from these scattered facts and instances, and from his own personal experience, the rudiments of that mighty and marvelous science which now bears his name, and will perpetuate his remembrance to the latest ages.