It is true that the parallel is by no means exact. The hypothesis requires us to suppose not merely that investigators of spiritualistic phenomena are liable to see, by hallucination, things which are not there, but also that they are occasionally withheld, by hallucination, from seeing actual movements and objects. For Mr. Crookes' automatic balance recorded a real movement; flowers and other objects have actually been brought into locked rooms; furniture has been demonstrably displaced, or has even moved before the eyes of the investigators, and been found at the conclusion of the experiment in its new position; an actual blister was raised on Lord Lindsay's skin by the touch of a live coal which Home held in a hand apparently bare. Now if these results were due to the action of known forces, muscular and other, it seems clear that some of the medium's movements and appliances escaped observation. We have, however, no record, so far as I know, of collective negative hallucination telepathically caused. But it may be pointed out that whilst it is only in unusual circumstances that a hallucination of the kind could attract sufficient attention to be recorded, negative hallucinations can be imposed without difficulty on a hypnotic subject. So that their telepathic origination in the circumstances suggested presents no greater à priori difficulty than that of positive hallucinations. There are, however, other differences between the collective hallucinations recorded in Chapter XII. and those which the hypothesis requires. For the former were for the most part vague and transitory, and were rarely shared by more than two persons; whilst the hypothetical hallucinations of the spiritualistic séance are persistent, and may affect several persons simultaneously and to an equal extent. It may be suggested, however, that the different conditions in the latter case—the common expectancy, the attunement of the minds of all present to a common mood, the absence of external solicitation to the senses—may be sufficient to account for the differing characteristics of the phenomena observed.
It may be objected that the problem does not require the intervention of such a Deus ex machina as collective hallucination; that fraud and malobservation are adequate to account for all the facts reported. I confess that I am unable so lightly to set aside the deliberate testimony of men of proved scientific distinction, whose word is still regarded as authoritative in observations not less delicate, and for results to the layman hardly less dubious. But I do not suggest that the phenomena, however interpreted, are likely to add anything to the proof of telepathy. I would merely urge that, as until the possibility of thought-transference in its various forms has been patiently and rigorously excluded, odylic flames and magnetic influences must remain unproven, so, in dealing with that residuum of evidence for the physical phenomena called spiritualistic which appears inexplicable by fraud and malobservation, the possibility of collective hallucination telepathically caused should be kept in view.[164]
It should be observed that the treatment of telepathy by those responsible for the word involves as little of theory as Newton's conception of gravitation. What Newton did was to find the simplest general expression for the observed facts by saying that the heavenly bodies acted upon each other with a certain measurable force. He did not attempt to explain the mode of this action. And whilst succeeding astronomers have for the most part been content to follow Newton's example, the science has, nevertheless, advanced in a steady and continuous progression. So the conception of telepathy simply colligates the observed facts of spontaneous and experimental thought-transference, as instances of the action of one mind upon another. The nature of the action the theory does not discuss; it merely defines it negatively, as being outside the normal sensory channels. In accordance with this view, Mr. Gurney, and the English investigators generally, have consistently employed psychical terms in their discussion of the subject: they have spoken of the transmission of ideas, not neuroses, and of the affection of mind by mind, rather than of brain by brain.[165] This treatment involves no prejudgment of the question. Whatever may be the nature of the cause, we know the effects at present only in their psychical aspect, and in default of a physical theory, as psychical it seemed convenient to discuss them. This mode of speech is of course as legitimate as the popular usage which permits us, when the sun's rays strike upon our retina, to ignore the intervening physical processes, and to express only the psychical result, "I see the sun." But Mr. Gurney and his colleagues were further influenced in adopting and maintaining this usage by a conviction that the advancement of the subject has not hitherto been dependent upon the discovery of physical correlates for the observed psychical action, and that the energy which would be diverted to the search for explanations, could be more fruitfully employed on the still imperfect demonstration that there is something to be explained.
But it is obvious that this attitude of reserve cannot be maintained indefinitely. Since Mr. Gurney wrote the sum-total of observations and experiments has steadily increased, and there is hardly any longer room for doubt that we have something here which no physical processes at present known can adequately account for. It is not possible to observe facts without speculating on the underlying law: it is the law indicated by the facts, more than the facts themselves, which is of permanent interest to the human mind. Nor indeed can any fruitful observation be long maintained, which is not accompanied, guided, and stimulated by theoretical speculation. Professor Lodge has called upon us, in this matter, to "press the doctrine of ultimate intelligibility;"[166] and in so saying he has at once given articulate expression to an impulse from whose blind urgency no student of nature can escape, and has formulated what is after all the differentia of the scientific mind. The average man accepts things as they are; the man of science presses the doctrine of ultimate intelligibility.
But however legitimate at the present stage of the inquiry theoretical speculation might seem, such speculation has for the most part been conspicuously wanting in the treatment of the subject by those best qualified to deal with it. At any rate the attitude of most continental investigators, like that of their English colleagues, has been a purely positive one. They have contented themselves with describing in psychical terms the psychical phenomena which they have observed. There are, indeed, some competent inquirers at the present time who incline to attribute thought-transference to the direct action of mind upon mind, or to some process yet more transcendent, just as in the last generation there were some who thought they were able to discern, in such instances as came under their notice, proof of the agency of disembodied spirits. And Von Hartmann, boldly accepting the facts wholesale, ascribes them to a communication between finite minds effected through the inter-mediation of the Absolute.[167] But until we have exhausted the resources of the world which we know, we should perhaps conclude, with Mistress Quickly, that there is no need to trouble ourselves with any such thoughts yet.
Any attempt at a physical explanation is, of course, beset with many difficulties. To begin with, there is no sense-organ for our presumed new mode of sensation; nor at the present stage of physiological knowledge is there likelihood that we can annex any as yet unappropriated organ to register telepathic stimuli, as the semicircular canals are supposed to register the movements of the body in space. In lacking an elaborate machinery specially adapted for receiving its messages and concentrating them on the peripheral end of the nerves, telepathy would thus seem to be on a par with radiant energy affecting the general surface of the body. But the sensations of heat and cold are without quality or difference, other than difference of degree; whereas telepathic messages, as we have seen, purport often to be as detailed and precise as those conveyed by the same radiant energy falling on the organs of vision.
As regards the mode of transmission, we find first the theory of a fluid, which owes its origin to Mesmer, and was in vogue at a time when fluids were still fashionable in scientific circles. Dr. Baréty[168] has recently revived this theory in a new form. He alleges that there is a nerve-energy (force neurique rayonnante) which radiates from the eyes, the fingers, and the breath of the operator, and is capable of producing various effects upon hypnotised subjects. He finds that a knitting-needle acts as a conductor for this force, and water as a non-conductor; that the nerve-rays can be focussed by a magnifying-glass, refracted by a prism, and reflected from a mirror or other plane surface at an angle equal to the angle of incidence. Dr. Baréty has omitted to state whether in the latter case the rays are polarised, nor has he shown whether the force varies inversely to the square of the distance. But the consideration of these remarkable results need hardly detain us long, since they can all readily be explained by suggestion, verbal or telepathic.
If we leave fluids and radiant nerve-energy on one side, we find practically only one mode suggested for the telepathic transference—viz., that the physical changes which are the accompaniments of thought or sensation in the agent are transmitted from the brain as undulations in the intervening medium, and thus excite corresponding changes in some other brain, without any other portion of the organism being necessarily implicated in the transmission. This hypothesis has found its most philosophical champion in Dr. Ochorowicz, who has devoted several chapters of his book, De la Suggestion mentale, to the discussion of the various theories on the subject. He begins by recalling the reciprocal convertibility of all physical forces with which we are acquainted, and especially draws attention to what he calls the law of reversibility, a law which he illustrates by a description of the photophone. The photophone is an instrument in which a mirror is made to vibrate to the human voice. The mirror reflects a ray of light, which, vibrating in its turn, falls upon a plate of selenium, modifying its electric conductivity. The intermittent current so produced is transmitted through a telephone, and the original articulate sound is reproduced. Now in hypnotised subjects—and M. Ochorowicz does not in this connection treat of thought-transference between persons in the normal state—the equilibrium of the nervous system, he sees reason to believe, is profoundly affected. The nerve-energy liberated in this state, he points out, "cannot pass beyond" the subject's brain "without being transformed. Nevertheless, like any other force, it cannot remain isolated; like any other force it escapes, but in disguise. Orthodox science allows it only one way out, the motor nerves. These are the holes in the dark lantern through which the rays of light escape.... Thought remains in the brain, just as the chemical energy of the galvanic battery remains in the cells, but each is represented outside by its correlative energy, which in the case of the battery is called the electric current, but for which in the other we have as yet no name. In any case there is some correlative energy—for the currents of the motor nerves do not and cannot constitute the only dynamic equivalent of cerebral energy—to represent all the complex movements of the cerebral mechanism."[169]
Considered purely in its physiological aspect, such a theory appears to present no special difficulty; or rather, to put the matter more exactly, our ignorance of the ultimate nature of nerve-processes is so nearly complete as to permit us to theorise in vacuo, with little risk of encountering any insuperable obstacle. It is true that Professor G. Stanley Hall,[170] in commenting on such physical theories of telepathy, maintains that they contravene well-established physical laws:—"The law of 'isolated conductivity,' formulated fully by Johannes Müller, which Helmholtz compares in importance to the law of gravity, first brought order into the field of neurology by insisting that impressions never jump from one fibre to another.... Is it likely that a neural state should jump from one brain to another, through a great interval, when intense stimuli on one nerve cannot affect another in the closest contact with it?" But it is clear that the "law" in question is merely a generalisation from observed facts, and from facts, moreover, not of the same order as those now under discussion. For the question here is not of the affection of another nerve-fibre in the same organism, but of a nerve-centre in another organism. And whilst it must have seemed à priori probable that between nerves belonging to the same system induction would not take place, because the alternative could hardly fail to be injurious to the organism, and that the susceptibility to such induction, if originally present, would have been eliminated in the course of evolution, it is at least theoretically conceivable that between different organisms induction might have persisted as innocuous, or even have been developed as positively beneficial.