The trip to Spain was merely an interlude; for, above all, at this time he felt the attraction of Japan. Returning from Europe in June he spent the summer in Dedham; but when winter came he started again for the Far East, this time by way of Europe, where he picked up Ralph Curtis; and then by the Red Sea to India and Burma, reaching Tokyo about the first of April, 1891. By far the most interesting part of this visit to Japan arose from a journey which he took with George Agassiz in July and August, into the interior of the Island. Agassiz became a most devoted friend, who followed his studies here, and later in Flagstaff, taking part in his observations and writing a memorial after his death. Their object was travel through a part of the mountainous region, ending at Ontake, a high extinct volcano, one of Japan’s most sacred peaks. But the holiness of the spot, or the religious pilgrimages thereto, were not the motive of the visit; nor did they expect to see anything of that nature with which they were not already familiar.

Leaving Tokyo by train on July 24, they soon reached a point where they got off and took jinrikishas to descend later to their own feet on a path that came “out every now and then over a view at spots where Agassiz said one had to be careful not to step over into the view one’s self.” For the next three days the lodging was not too comfortable, the heat terrific and the footpath going over a steep mountain pass. However, the weather improved; and without serious misadventure they were, on August 6, ascending Ontake, and not far from the top, when they saw three young men, clad as pilgrims, begin a devotional ceremony. One of them seated on a bench before a shrine, went through what looked like contortions accompanied by a chant, while another, at whom they were directed, sat bowed on the opposite bench motionless until, beginning to twitch, he broke into a paroxysm and ended by becoming stiff though still quivering. Then the first leaned forward, and bowing down, asked the name of the god that possessed his companion. The other in a strange voice answered “I am Hakkai.” Whereat the first asked, as of an oracle, questions that were answered; and after the god had finished speaking, said a prayer and woke the other from his trance. But this was not the end, for the same thing was repeated, the three changing places by rotation until each of them had been petitioner and entranced. On several more occasions the ceremony was enacted during the next thirty-six hours, the young men fasting all that time. The whole scene is more fully described in the opening chapter of Percival’s “Occult Japan.”

With his temperament and literary ambition he thought at once of writing about this extraordinary sight, which he connected as a phenomenon with the fox possession he had already encountered on a lower plane. He suggested the title “Ontake, a Pilgrimage,” but he soon saw the whole matter on a larger scale. The cult seemed to be unknown beyond its votaries, nothing did he find written upon it, the few foreigners who had scaled the mountain had missed it altogether, although, as he says, their guides or porters must have been familiar with it. Dr. Sturgis Bigelow, who was a student and believer in Buddhism, had never heard of it, which seemed strange, for although a Shinto, not a Buddhist, rite many people accepted both faiths, and one Buddhist sect practiced something akin to it. Moreover, its underlying idea of possession by another spirit appeared to ramify, not only into fox possession, but in many other directions. On inquiry he found that there was an establishment of the Ontake cult in Tokyo, and the head of it the Kwancho, or primate of that Shinto sect. This man proved very friendly and gave all the information about its rites, their significance and underlying philosophy, within his knowledge,—perhaps beyond it,—and arranged exhibits; all of which Percival carefully recorded in his notebooks. Every motion made in inducing the trance, every implement used in the ceremony, had its meaning and its function, which he strove to learn. Moreover, there were miracles of splashing with boiling water, walking over hot coals and up ladders with sword blades for rungs; curing disease; consulting the fox and the raccoon-faced dog, which he called Japanese table turning; and other less dignified performances more or less connected with the idea of divine or demonic possession. Some of these things he was able to witness by sÉances in his own house, others by visits to the places where they were performed, often for his special benefit.

All this took more time than he had expected to spend in Japan, and delayed his sailing until the autumn was more than half over. Nor was this enough to complete his researches. In December of the following year he re-crossed the Pacific, and at Christmas we find him at Yokohama. Again he hires a house, fits it up in Japanese style but with occidental furniture; again he was travelling over the land, this time in search less of scenery than of psychic phenomena and the lore connected with their celebration. In July he is interviewing a Ryobu Shinto priest and “eliciting much valuable information.”

For the trances, and the various miracles, a participant must be prepared by a process of purification, long continued for the former, always by bathing before the ceremony; and by Percival’s frequent attendance, and great interest, he attained the repute for a degree of purity that enabled him to go where others were not admitted. On this ground he attended what he called the Kwancho’s Kindergarten, but was not allowed to bring a friend. The Kwancho, as the head of the principal Shinto sect that practised trances, had a class of boys and girls who went through a preparation therefor by a series of what an unbeliever might call ecstatic acrobatic feats, lasting a long time before they were fitted for subjects of divine possession. He visited everything relating to the mysteries that he could find, procured from the Kwancho an introduction that enabled him to see the interior grounds of the great shrines of Ise, from which even the pilgrims were excluded, and to see there a building whereof he learned the history and meaning that the very guardian priests did not understand. At trances he was allowed to examine the possessed, take their pulse, and even to stick pins into them to test their sensibility, sometimes in a way that they were far from not feeling afterwards. In short he was enabled as no one had ever been before, to make a very thorough examination of the phenomena with the object of discovering and revealing their significance; for he was convinced that they were perfectly genuine, without a tinge of fraud, and allied to the hypnotism then at the height of its vogue. In March, 1893 he gave the first of a series of papers on Esoteric Shintoism before the Asiatic Society of Japan. These he worked up after his return to America in the autumn, and published in 1895 with the title “Occult Japan or the Way of the Gods.”

A casual reader might be misled by occasional cleverness of expression into thinking the book less serious than it is. Perhaps that accounts in part for Lafcadio Hearn’s calling it supercilious. Percival himself says, in the first paragraph of the chapter on Miracles: “It is quite possible to see the comic side of things without losing sight of their serious aspect. In fact, not to see both sides is to get but a superficial view of life, missing its substance. So much for the people. As for the priests, it is only necessary to say that few are more essentially sincere and lovable than the Shinto ones; and few religions in a sense more true. With this preface for life-preserver I plunge boldly into the miracles.” In fact, expressions that appear less serious than the subject merits are few, and the descriptions, of the trances for example, are almost strangely appreciative, and for a scientific study keenly sympathetic and beautiful.

The book opens with an account of the trances of the three young men on Mount Ontake, for that sight was the source of all these researches. He next lays a foundation for the study of the subject by a short history of the Japanese religions; how Shinto, the old cult, with its myriad divinities and simple rites, was for a time overshadowed by Buddhism, to be restored with the power of the Mikado; and how with its revival the popularity of the trances returned. They had been kept alive by a single Buddhist sect which had adopted them, but now they are even more widely practised by two out of the ten Shinto sects, their sacred site being Ontake. But before taking up the trances he describes the lesser, and better known, cases of miraculous intervention for protection from injury and for sanctification; notably, being sprinkled with boiling water, walking over a bed of hot coals, and up and down a ladder of sword blades; and he discusses why no injury occurs. The walking over hot coals, at least, was even performed in his own garden; and, although he does not say so in the book, he did it himself, without, however, complete immunity to the soles of his feet.

After telling of what he terms objective, as distinguished from subjective, miracles, such as bringing down fire from heaven; and saying something of miraculous healing of disease, he comes to the main subject of the book, the incarnations or trances. First he speaks of the preparation for them, washing and fasting which are arduous and long, the purification of persons and places, and a series of ceremonies which, he says, tend to promote vacuity of mind. All these things are absolutely sincere, for he declares that the first view of a trance dispels any idea of sham. He then describes three typical trances: first Ryobu, a Shinto-Buddhist sect, where one of the men possessed, on coming back to himself, was disappointed that he had not spoken English, which he did not know himself; for to his mind it was not he that spoke but the god who entered into him. The second example was a Buddhist trance with the full complement of eight persons filling their several offices in the ceremony. This description is especially striking and sympathetic. The third case is of a pure Shinto trance, much the same, but with the simpler ceremonial of that cult. He describes also the Kwancho’s training school, which has already been referred to as the Kindergarten. He notes the pulse, insensibility, the other physical conditions and sensations of the possessed, the sex and number of the gods who enter him, for the exorcist has no power to invoke the spirit he would prefer, but simply calls for a god, and when one comes inquires who it is. It may be a god or a goddess, and several of them may come in succession. The main object of the proceeding being to obtain counsel or prophecy, the exorcist, and he alone, can ask questions of him, but he can do so on behalf of anyone else, and often did so for Percival about his own affairs, although the prophecies appear never to have turned out right.

A chapter is devoted to pilgrimages and the pilgrim clubs, which included in the aggregate vast numbers of people, only a minute part of whom, however, belonged to the trance sects. They subscribed small sums to be used to send each year a few of their members to the shrine or sacred mountain with which the club is associated; this feature of the religious organization being as important from a social as a religious point of view. Another chapter is given to the Gohei, or sacred cluster of paper strips, used for all spiritual purposes, and essential in calling down any god; an emblem which he compares with the crucifix, while pointing out the difference in their use. This first part of the book ends with an argument, apparently to one who knows nothing about the matter conclusive, that the whole subject of these trances is of Shinto not Buddhist origin; and in this connection he tells of his visit to the shrines of Ise where a temple was built to the sun-goddess when she possessed people, as she has long ceased to do at these shrines.

So far the book is scientific; that is, it consists of a description and analysis of phenomena repeatedly observed and carefully tested. The second part, which he calls Noumena, is an explanation of them on general psychological principles, and thus belongs rather to philosophy than science. It comprises discussions of the essence of self, of the freedom of the will, of the motive forces of ideas, of individuality, of dreams, hypnotism and trances. In these matters he was much influenced by the recently published “Psychology” of William James, which he had with him, and he draws comparisons with hypnotism, a more prominent subject then than it is now. Bearing in mind his dominant thought about the essential quality of the Japanese, it is not unnatural that he should find in the greater frequency of such phenomena among them than elsewhere a confirmation of his theory of their comparative lack of personality.

Perhaps his own estimate of the relative value of the two parts of the book and that of critics might not agree; but, however that may be, the second part is penetrating, and the work as a whole a remarkable study of a subject up to that time practically wholly concealed from the many observers of Japanese life and customs. It was, in fact, his farewell to Japan, for, leaving in the fall of 1893, he never again visited that land. Ten years its people had been his chief intellectual interest, but perhaps he thought he had exhausted the vein in which he had been at work, or another interest may have dislodged it. He has left no statement of why he gave up Japan for astronomy, but probably there is truth in both of these conjectures.