The Human Atmosphere: Chapter IV. Optical Problems

THE human aura is invisible in total darkness, and can best and most easily be seen in a dim light, when the eyes are in an incompletely dark adapted state. As this condition is of great importance in relation to various problems that will require discussion, a short and concise account of it will not be out of place. Without taking into consideration any except the most elementary physiological facts, it is well known that in the normal and healthy eye the iris is contracted more or less in proportion to the brilliance of the light. (Changes relating to accommodation will not be referred to here.) The aperture of the pupil is consequently small and allows external objects to be focused as sharply as possible on the fovea. This part of the retina is composed of cones which- are colour-sensitive to all the rays of the ordinary visible solar spectrum. Mixtures of these rays in certain proportions will cause the sensation of white light, while light of a single wave length or of mixtures of wave lengths other than in proportion to produce white light, cause colour-sensations.

In the dark adapted state the iris becomes more dilated and the eye more sensitive to slight changes of illumination. The larger pupil also permits more light to pass, which of itself is an advantage in a dim light, but what is still more important it allows a larger portion of the retina to be illuminated. This fresh portion of the retina differs from the fovea inasmuch as it contains a great number of rods far

outnumbering the cones as the periphery is reached. The rods are considered colour-blind and their stimulation only produces a grey sensation. They are acted upon chiefly by the shorter and more refrangible rays. In the dark adapted state the point of maximum luminosity has been removed towards the violet end of the spectrum to the yellow-green.

It is highly important to determine, if possible, how the dicyanin screen enables the aura to be perceived. The solution of this question depends partly upon the attributes of the aura itself, but to a still greater extent upon the action exerted upon the chemical upon the eyes.

On one occasion before systemic examinations of the auras .had been undertaken, a lady wished to see the haze round the arm and hand. A dark blue screen was given to her to look through at the light, but after using it she was quite unable to see the aura. In the meantime it had been noticed that a methylene blue screen had inadvertently been handed to her. She was allowed to use it without being informed of the mistake, because this was regarded as a good test of the comparative value of the two screens. She afterwards looked at the light through the proper screen, and immediately the blinds had been regulated, could detect the aura. Twice again at different times has the methylene blue screen been unconsciously substituted for a dicyanin one, and it has also been tried intentionally several times and always found inert.

Reichenbach, in his "Researches on Magnetism," gives instances of over fifty sensitives who were able to see light proceeding from magnets, etc., in total darkness. Unless all these people were frauds (and there is no reason to class them as such), they must either have possessed very acute sight, which enabled them to detect an illumination too faint to produce any sensation in ordinary men and women, or else

that the quality of their sight was different, and permitted them to descry phenomena usually invisible. This latter supposition is probably correct, the force emanating from magnets, etc., producing vibrations situate at some distance beyond the ordinary visible Solar Spectrum. The same, too, may be true of the human aura. One reason for coming to the above conclusion is, that if the effective undulations are identical with those at any part of the visible spectrum, there should be a large number of people with sufficiently acute vision to have observed so remarkable a phenomenon at the poles of a magnet and the somewhat similar appearances here referred to as the aura. This argument will be still further strengthened if it can be proved that clairvoyants do not possess more than the average acuteness of vision for all ordinary purposes. A clairvoyant was consulted and kindly replied that "the gift was in no way connected with the ordinary sight," and in fact that some clairvoyants have inferior ordinary vision. Under these circumstances it may be safely concluded, that individuals who can see the human aura and the haze round magnets, etc., obtain their powers, not from keenness of sight, but from ability to see rays not included in the ordinary visible spectrum.

If some people are able to distinguish undulations outside the usual visible spectrum, there would seem to be no particular reason why, by the aid of some apparatus, or even by treatment of the eyes, others should not be able to do the same. This is exactly what is claimed for dicyanin.

Although from the very first it was recognized that dicyanin exerted a peculiar influence upon the organs of sight, yet for a long time the part of the eyes affected and the nature of the change brought about remained utterly incomprehensible, and any attempt at an explanation can even now be only hypothetical.

Nine or ten years ago, when the writer was investigating by mechanical means forces emanating from the body, a beam of light reflected from a small movable mirror (similar to those used for galvanometers) upon a scale was employed, and as it was necessary to read accurately the deflection at a distance of eight feet, use was made of a pair of opera glasses that required to be racked out to the full extent for clear vision. One day some years later, happening to look through the glasses, he found to his surprise that they did not need the same extension for perfect vision, even though the object was only half the distance away. The only feasible explanation that can be offered for this occurrence, is that the focal length of his eyes had in. some manner been shortened virtually or absolutely, and as no other cause was forthcoming, the effect could only be attributed to the constant peering through the dicyanin screen. That some alteration has taken place in his eyes, is confirmed by the fact that the time of the visual examination of the aura was commenced (over ten years ago), the writer was contemplating buying stronger spectacles, which, as he ceased to be troubled by his sight, he forgot to do and he has not done to the present day, moreover his reading distance has actually diminished, though accommodation, of course, has not improved.

Shortly after this discovery, a friend, a medical man, mentioned that a gentleman to whom he had been showing the aura by means of the dicyanin screen, did not need glasses for reading or writing for over twenty-four hours afterwards, although previously he could not distinguish print properly without their aid. These two cases led to the conclusion that it was quite possible that the dye might to some degree affect a number of people in a similar manner, and might perhaps furnish at least a partial explanation of the occular changes required before

the aura can be seen. But before describing the experiments undertaken to put this idea to the test, it may be remarked that several other instances have been met with where persons after using dicyanin screens have taken up a hook or paper and have proffered the information that they were able to see the print without glasses better than they could ordinarily. The two following are amongst the first recorded cases. A lady, while her husband was talking, took up a book and exclaimed "that she could read it quite easily without spectacles," which, by the way, she had left at home, "a thing she had not been able to do for years." In the second instance, a medical man, after an allusion to the property of dicyanin under discussion, tried to read a newspaper without glasses. In general, he could only accomplish this when he held the paper out at full arm's length, but now he found that he was able to read it when held six to eight inches nearer.

Every person who has remarked upon his or her sight being temporarily improved, was presbyopic, though not to any great extent. The effect has never been noticed in emmetropia or myopia.

As it seemed impossible that coloured screens could influence accommodation, all experiments were conducted from the point of view of the other functions of the eyes. For this purpose a microscope was used, on which the fine adjustment lowered or raised the objective 1/100 of an inch for each revolution. The wheel was divided into ten parts, so that each division corresponded to 1/1000 of an inch. In table 3 this unit is denoted by the letters mi (mille-inches). The lowest eyepiece and the inch and a half objective were employed. Screens were prepared by filling glass cells with weak aqueous solutions of different dyes—carmine, K yellow, methylene blue, and gentian violet respectively. The exact depth of the colours seemed immaterial provided they permitted sufficient illumination

of the object on the stage, but this condition unfortunately introduced a disturbing factor, viz., the large amount of white light which passed through the screens.

The procedure adopted was as follows: The observer focused a selected bristle of the proboscis of a blow-fly (the object used) as sharply as possible by means of the coarse adjustment, the fine adjustment being placed at zero. Directly a sharp image had been obtained, he looked away for a second or two and then glanced at the object as quickly as he could, to determine whether the focus was correct. Further adjustment was made if required. This was done two or three times to ensure the elimination of accommodation effects.

A coloured screen was then inserted between the mirror and the object. The bristle had now to he focused a second time. This time the fine adjusting screw alone was used, with the same precautions as before. This procedure was repeated with each filter-screen in turn, the position of the fine adjusting wheel being noted for every observation and the results recorded.

The observer next looked at the light through the deep dicyanin screen for about thirty seconds, and then repeated the whole series of observations, focusing the object first in white light, and afterwards through each filter-screen in rotation.

The following is a detailed account of one experiment. The experimenter (A in the table) taking the precautions mentioned above, focused the bristle with the coarse adjustment, the fine adjusting standing at zero. The result was called O. A yellow screen was then placed under the object, which remained in perfect focus. Result O. The filter was then changed for a red one. The bristle was no longer in focus, to rectify which the wheel had to be turned one tenth of a revolution in the direction that lifted the objective

away from the object. The result was designated -1 mi. A blue screen was now inserted, and the fine adjusting wheel had to be rotated one division from zero in the opposite direction. This made the objective approach the slide, and the effect was termed +1 mi. With the violet filter sharp definition was not attained until the wheel had been turned two further divisions, altogether three tenths of a revolution, or +3 mi.

The observer next peered through the dark dicyanin screen at the light for about thirty seconds, and then refocused the object without the intervention of any screen, when it was found necessary to lower the objective +2.5 divisions from zero, which result was duly recorded. The red, yellow, blue and violet screens were then inserted in turn, but between each trial the observer looked at the light through the dark dicyanin screen for a few seconds. The resultant figures were for red +1 mi., yellow +1 mi., blue +2 mi., and violet +3.5 mi. This observer was tested on three separate occasions, and the readings obtained showed no variations.

Most of the observers in these experiments were medical men, and every one was experienced in the use of the microscope. Only those results (fifty in number) which passed the strictest tests as detailed above were kept. One or two observers did not take sufficient pains, but the cause of most failures was the difficulty in overcoming accommodation. During each series of experiments the focus of the microscope was purposely disturbed two or three times, when practicable, without the knowledge of the observer, and unless the re-adjustes completely coincided with the original readings, the series was rejected. Consequently not more than one series out of every three or four was accepted.

It was interesting to notice that the greater the alteration of the focus required after looking through

the dicyanin screen, the more easily was the aura perceived. In no case when the change for white light after the use of the dicyanin screen exceeded that requisite after the insertion of the blue screen alone, was there the slightest difficulty in seeing the aura. When the dicyanin produced a less effect than did the blue screen, the more nearly the readings approximated, the more readily did the observer perceive the aura. If a microscope be used for ascertaining whether a person is likely to see the aura easily, it will be unnecessary to traverse the whole series of tests. The following procedure will be quite sufficient: First focus the object in ordinary light, next with a blue screen beneath the object, and lastly again in daylight after looking through the dicyanin screen. Unfortunately, however, this method can rarely be employed, as few people are sufficiently conversant with the use of the instrument.

Some observers find it difficult to obtain a good definition when the violet screen is beneath the object. The trouble is due to the fact that the dye (gentian violet) used gives two bright bands with spectroscope, with one maximum between 4,000 λ and 4,500 λ, and the other between 6,500 λ and 7,000 λ *. (Vide Mees’ "Atlas of Absorption Spectra.") The colours being so far apart in the spectrum are antagonistic to one another. The violet screen has only been retained for convenience, as very little importance can be placed upon results obtained by its aid. It ought to be borne in mind that the violet in the spectrum consists of wave lengths adjacent to each other, while all the violet pigments and dyes are merely mixtures of red and blue.

In table 3 the first three series were obtained by observers who were under the age of forty, the next three between forty and sixty, and the third over the

TABLE III

	WHITE	RED	YELLOW	BLUE	VIOLET
A	0	-1	0	+1	+3
	+2.5	+1	+1	+2	+3.5
B	0	-1	0	+2	+4
	+3	+1.75	+2	+2	+4.5
C	0	-1.5	0	+2.5	+2.5
	+2.5	+0.5	0	+2.5	+2.5
D	0	-1	0	+1	+3
	+1	+0.75	+0.75	+1.5	+3.5
E	0	-1.5	0	+1.75	+1.75
	+2	+0.5	+0.5	+1.75	+1.75
F	0	0	+1	+1
	+2.5	+1	+1	+3
G	0	-1	0	+1.5	+2
	+1	-0.5	0	+2	+2
H	0	0.75	0	+1.75	+1.75
	+1	+0.25	+0.75	+2	+2
I	0	-1	0	+1
	+1.5	+0.5	0	+1
J	0	-1	0	+2.5
	+2	0	+1	+2.5
K	0	-1	0	+2.5
	+6.5	+2.25	+5.25	+6
L	0	-1	+0.09	+2.4
	+2.25	+07	+1	+2.8

age of sixty. The tenth observer was a medical student whose accommodation was temporarily suppressed by atropine, the eleventh that of a clairvoyant. The last readings are the means of fifty cases. The upper reading of each series is before, and the lower after looking at the light through the dicyanin screen. The figures explain why persons over the age of fifty years have greater difficulty of seeing the aura at their early trials than younger people.

The eleventh case is extremely interesting as the observer was a clairvoyant, and the writer was especially gratified at meeting her, because he had often wondered how far clairvoyant's eves differed from the normal in ordinary respect. Fortunately this lady was quite expert with the microscope and was painstaking. Her husband was the possessor of a very fine instrument which she was in the habit of using. It will be noted that before looking through the dicyanin screen, the coloured filters under the microscopic object only produced the average effect upon her eyes. The dicyanin had, however, a greater influence than in any other instance met with before or since. This was the lady previously referred to as being able to see better without her glasses than she had done for years. (Page 61.)

In order to appreciate these experiments to the full extent, it is necessary to recall a few details of elementary physics. Ordinary daylight is well known to consist of undulations in the ether of different wave lengths. The visible solar spectrum is divided into six main divisions (purposely omitting indigo), viz., red, orange, yellow, green, blue and violet. If a quartz prism be used there is a portion of the spectrum lying beyond the violet named the lavender-grey, which some people cannot see. The intensity of the luminous spectrum in daylight is greatest near the yellow region, from which point it gradually diminishes towards the red and violet ends. There is no physical reason why the yellow should be more energetic than any other colour of the spectrum, and the cause is purely physiological.

Although full of marvels the human eye is by no means a faultless optical instrument. It is imperfectly corrected for chromatic aberration, since the various colours come to a focus on different planes. The red being the least refrangible, has its focus furthest from, and the violet nearest, the lens. The

focus of the yellow is about midway between the red and the violet, and in the normal eye the yellow rays fall exactly on the retina, while the other colours come to a focus a little in front or behind it. Correction is arranged for in the brain centres. Since the red rays are focused behind the retina, the lens would have to be moved slightly forwards in order to make them fall exactly on the retina. This is equivalent to moving the objective of the microscope a little further from the object. The blue and the violet rays on the other hand would require the lens to be shifted nearer the retina, tantamount to bringing the object glass closer to the object.

Thus when the object has been first focused in white light, and again after the coloured filters have been inserted beneath the object one after another, it will be necessary to move the objective further from the slide for the less and nearer for the more refrangible rays.

Now to return to the dicyanin screen. Before looking at the light through this screen in the experiments just detailed, red was the only colour negative to the white and yellow, while the blue and violet were positive. In the series fully described the observer A, after having peered through the dicyanin screen, found red, yellow and blue all negative, while the violet remained positive but only to a small extent. This becomes more evident if + 2.5 mi. * be deducted from each of the figures, making the corrected readings for red -1.5 mi., yellow -1.5 mi., blue -0.5 mi., and the violet -1 mi. These experiments prove that some alteration has taken place in the eye equivalent to a lengthening of the eye, or a shortening of the principal focus, which enables presbyopics to read without glasses. It would also appear that white and yellow rays, at or near the

[paragraph continues] D line, come to a focus at the true principal focus of the normal eye; in the eyes after exposure to the dark dicyanin screen, rays on the violet side, probably in the yellow-green or green, come to a focus at that point, and thus possibly the phenomenon is associated with the extension of the visual powers into the regions of the spectrum beyond the usual limits. The impression induced upon the sensitized eye by a visible aura, etc., might then be the result, at least partially, of the action of ultra-violet rays. This, too, would be the explanation of the colour variations and changes as seen with or without screens or complementary coloured bands. Great support is given to this hypothesis by the fact that the greater the alteration produced by a dicyanin screen in the focusing test of the microscope, the easier it is to see the aura.

It is evident from these experiments that dicyanin has the power of shortening the focus of the eye, yet there are very great difficulties in determining the way this is achieved. Accommodation, as it apparently remains unaltered, seems to take no part in the transaction, and as yet no test has been devised, the question must be treated entirely theoretically. For this purpose the eye has to be considered under three different aspects, viz., the physical, the chemical and the nervous.

The equivalent of shortening the principal focus of the eye can be obtained by:—

1. Increase of the curvature of the cornea or lens. This proposition is so improbable that it requires no consideration.

If the change be due to this cause, the fluid media will be the most likely parts to be affected.

a. The first of these assumptions could not take place during the short time of peering through the screen.

b. The second would be merely an incipient glaucoma, and the repetition of the sensitizing of the eye might cause all the inconvenience of this disease. As no stage of this affection affords symptoms at all similar to those produced by dicyanin, this proposition gives no help.

c. It thus seems that a chemical change is the only possible explanation of the production of an increase of the refractive index. What the alteration consists of cannot be imagined, but that a true modification has really taken place is strengthened by the peculiarities in the colour perception as will be considered later on.

Even though it is unreasonable to imagine that a shortening of the focus of the eye can be accomplished directly through nervous agency, yet there is good cause to suppose that dicyanin exerts an influence upon the nervous system of the eye; either on the retina or the central ganglia, separately or in conjunction. Comparison between the two following experiments, one diminishing and the other adding to the efficiency of the eye, is instructive.

Exp. 1. Let a person look at a primary coloured band as directed in chapter vi, only colour-blinding one eye instead of two. If he then looks at a white screen with both eyes the complementary coloured band is visible. If he closes the unaffected eye the spectre still remains. If he shuts the colour-blinded eye no complementary coloured band can be observed.

Exp. 2. A lady who had never seen the aura tried to detect it under the most favourable conditions of light and background, but completely failed. One eye was sensitized with dicyanin in the usual manner, while the other was closed. The result was that she could immediately see the aura when looked for with

both eyes. It was equally plain when she closed the non-sensitized eye. When she used the latter alone she could see the aura, but not so distinctly. After peering through the dicyanin screen at the light with both eyes, each eye was equally perceptive.

Exp. 3. A, failed to see the aura, but after sensitizing one eye by means of the dicyanin screen, he found both eyes were equally efficient, although not quite to the same extent as when he had subsequently peered through the screen with both eyes in the ordinary manner.

Exp. 4. P, was unable to perceive the aura. After sensitizing one eye only with the dicyanin screen, she remained incapable of detecting it, when either using one or both eyes. After looking at the light through the same screen in the ordinary manner with both eyes, she obtained the power of seeing the haze.

Exp. 5. G K, looked for the aura but could not sec the slightest sign of it. He then looked at the light with his right eye for about thirty seconds through the dicyanin screen, while he closed and covered the left. Directly afterwards he could distinguish the aura with his left eye, but it was not quite as distinct as when the right eye was used alone. Sensitizing both eyes increased the efficiency slightly.

The inferences from these experiments are intricate and very difficult to interpret. The only explanation that seems to be forthcoming is that the observer has naturally a slight power of the perception of the aura, but so slight as to be latent until it has been aroused by some outside stimulation. This idea is strengthened to some extent by a lady who tried to see the aura without having peered through the dicyanin screen and completely failed. However, she persevered for some ten minutes, when she said that she thought she

could see the haze but was uncertain whether the impression was not merely imagination. Her eyes were then influenced by the dicyanin screen when she could immediately distinguish the aura plainly, there being no difference to what she had noticed before except in distinctness.

The next step is the consideration of the conditions in which the aura can be seen. The most favourable is a dim light (not complete darkness), which is also best suited for practical work. The haze can often be seen round any part of the human body against a dark background in ordinary daylight when viewed through coloured screens.

The depth of shade required for these screens is dependent upon the brightness of the light. Advantage of this method has been taken for the examination of the inner aura through the red or carmine screen. (Chapter iii.) Many screens of different colours have been experimented with in order to obviate, if possible, the necessity of a dark room, but none have been found to be sufficiently satisfactory. Taking all in all, a dark blue screen is most efficient for seeing the outer aura, but it does not reveal the peculiarities of the inner aura as plainly as the red. Some people can see the aura in ordinary daylight to a greater or less extent.

The inference that can be drawn from the above statements is that a dark adapted state of the eye is not an absolute necessity for the perception of the aura, but that this phenomenon can be far better observed when the eye has been partially reduced to this condition. It must be borne in mind that the need of a dim light may be partially due to the delicacy of the aura, whose visibility is destroyed by a bright light.

It is well recognized that an object that affords only a slight colour stimulus, when first seen in the incomplete adapted state, is grey and gradually

becomes coloured. The progressive development of colour depends upon the advance towards complete adaptation or on an increasing strength of colour stimulus. This tallies with the appearance of the aura, which at first looks grey and then shows an addition of some colour, usually blue or green.

It was mentioned a little time ago that one of the effects dicyanin had had upon the eyes was to confer the power of perceiving ultra-violet rays, and this supposition will be still strengthened by the study of the auric colours, which will now be done.

For our present purpose it is immaterial whether the undulations of different wave lengths are discriminated in the nerve centres, or whether they are separated in the retina by the nerve-endings of the fibres which convey the stimulus to and originate in the brain the perception of light, or by fluorescence of the media of the eyes.

These colours must be fully studied. Screens are necessary for their investigation, and it has been ascertained by experiment that deeply coloured ones are to be preferred, as by using them a fair amount of light may be allowed in the room; otherwise the exact depth of colour is of no consequence. The screens employed are:—

Before considering the effects of these screens upon the aura, it will be advisable to say a few words about their action under ordinary circumstances.

According to a widely accepted theory, the eyes possess three sets of colour-sensitive nerves, that are excited by red, yellow, * and blue respectively, and all other colours are perceived as a consequence of excitation of two or more of these nerves in varying degrees simultaneously.

The spectrum of ordinary daylight decomposed by means of a prism consists of a vast number of undulations of different wave lengths, that produce rainbow hues (the visible portion of the solar spectrum), besides many others that are commonly invisible. From a physical point of view the undulations of each colour and each shade of colour are quite distinct, and the notion of primary and secondary colours is entirely physiological. While slight variations exist in different individuals, yet for all practical purposes the spectral colours about Frauenhofer's lines B.D. and F. (about 6900λ, 5900λ, and 4870λ, respectively), may be regarded as the three primaries with sufficient accuracy for the following speculations.

Suppose a ray of light consisting of undulations of 6900λ, or thereabouts enters the eyes, it will influence the red-sensitive nerves most, and will appear to the observer, red. As the wave lengths become smaller, say about 6400λ, they will stimulate both the red and the yellow-sensitive nerves, giving rise to the sensation of orange. The wave lengths when reduced to about 5900λ, will be seen as yellow. In like manner as the undulations lessen gradually in size from 5900λ, to 4870λ, the observer will perceive yellow-green, blue-green, and lastly blue one after the other. Indigo will be left out. Subsequently a most interesting colour will be reached, viz., violet which roughly extends from 4200λ, to 3950λ. These rays not only excite the blue-sensitive nerves, but also stimulate the red-sensitive ones. Thus at one end of the visible solar

spectrum there exist red rays that excite the red-sensitive nerves to a greater or less extent, and at the other end there are undulations composed of very different wave lengths, that influence the same red-sensitive nerves, although in the intermediate parts of the spectrum as the wave lengths diminish the stimulation of the red-sensitive nerve endings lessens until it practically ceases.

When a quartz prism is used to decompose sunlight, a lavender grey colour is found beyond the violet. The visibility of this portion is probably due to fluorescence of the media of the eye, when the shorter invisible wave lengths are converted into longer and visible wave lengths. Beyond these again are undulations which cannot be detected by the unaided eye.

As a possible explanation of the visibility of the aura and of the various colour phenomena associated with it, the writer would suggest that the dicyanin screen brings about some change in the eyes, so that sensations not merely of light but also of colour, may to some extent be evoked by at any rate parts of the ultra-violet spectrum. It is not difficult to conceive that under such circumstances by an extension of the processes which occur at the violet end of the ordinary visible spectrum, when the red-sensitive nerve endings of the retina are again and with diminishing wave lengths increasingly stimulated, there might occur a more or less complete repetition of the spectral colour series probably greatly modified in many respects. In short a second, higher spectrum. Violet bears the same relationship to blue and ultraviolet red as orange does to the red and yellow.

Coloured objects reflect hues differing from those of the spectrum, inasmuch as the colours perceived may be the outcome of a combination of the various parts of the spectrum, on account of certain undulations being absorbed from white light. The reflected rays are rarely simple, being usually mixed with white light, because the object is generally unable to absorb

the whole of any one set of waves contained in the light falling on it. For instance, a green object may reflect:

3. Either 1 or 2 with the addition of white light. The resulting shade of green perceived being dependent upon the sum total of the action upon all the colour-sensitive nerves.

When objects are examined through various coloured screens, should the colour of the object and the screen differ only in shade, the former will appear darker or lighter in hue as the latter is paler or darker. If the object and screen are of the same colour and shade, the object will remain unaltered in hue. (See page 38.) Should the screen and the object be of different colours, according to the depth of the former, the latter will become much darker, or may be changed in hue from the admixture of the two colours. For example take a yellow object. This will look dark approaching to black if the screen be a very deep blue, while if light, it will change in colour, becoming greenish from the intermingling of the blue and yellow.

Almost every observer after using the dark dicyanin screen sees the aura as a blue or blue-grey mist. The question arises whether this blue colour is due to wave lengths of about 4200λ, or belonging to a region beyond the ordinary visible spectrum. If the former it must be due to ordinary reflected light, and should follow the ordinary laws when examined through the coloured screens; if the latter some departure from the usual appearances might not unreasonably be expected.

The investigation demands that the observer should be able to detect the aura without using the pale dicyanin screen; have no deficiency of colour vision; and be capable of describing accurately the colours

he sees; consequently an artist, if able to perceive the aura, is the ideal person. It is curious that when examining the aura through the various screens, no two experimenters give identical names to the colours they see. The cause may be sometimes due to imperfections in their descriptive powers, as the colours are constantly weird and almost indescribable, but the discrepancies at other times are so pronounced that it is impossible to doubt that their visual organs were differently affected, although under ordinary circumstances colours are correctly named. The weird effects seem frequently to be produced by the non-blending of two or more colours seen simultaneously. For instance blue and yellow are often seen as blue and yellow, not green as might be anticipated; and red and blue do not necessarily make a violet or purple. In some cases it is likely that a partial combination does take place, complicating matters still more, so that blue and yellow not only appear separately but also as mixed as green, making a strange jumble of colours.

These peculiar impressions may be explained by supposing that as whereas the sensations due to simultaneous stimulation by yellow and blue are combined into green by the brain, the colours seen in relation to the aura being outside ordinary experience are recognized with the curious results already mentioned.

An artist's model stood in front of a black background, with her hands on her hips and her elbows extended, while the auras in the interspaces between the arms and body were examined. O, an artist by profession, when not using any screens, described the aura as a haze of which the colour was a blue and grey. The appearance was the same throughout the spaces, except the part nearest the body (evidently the inner aura), which was rather more pronounced. He next examined the aura through

coloured screens, and the results are tabulated in series 1 of table 4. (pages 80 and 81). The model was then asked if she could change the colour on the left side to red. She succeeded only in producing a red-grey colour. Afterwards in like manner a very good blue was produced on the right side. Through the screens O saw the hues mentioned in series 2 and 3 of the table. The model next tried to produce a yellow on the right side, but the resultant colour being unstable was not very useful for a series of tests. However, it appeared a warm green through the first screen employed, which happened to be a yellow. It frequently occurs that a change in the colour of the aura when brought about by voluntary efforts, is not sustained sufficiently long to allow of complete examination through all the screens.

At various times in connection with similar experiments the writer has inspected this woman's aura through coloured screens. The results are given in series 4 to 7 of the table. Series 8 and 9 are the colours recorded by Q, and the writer, which without the intervention of any screen appeared a liquid French ultramarine.

The other examples in the table were chosen to illustrate the colours seen during health. During illness alterations of the colours of the aura when viewed through different coloured screens, especially the blue one, are very frequent, and in a large proportion of cases some shade of yellow is present.

The above observations suffice to show that the natural hue of the aura remains a blue when looked at through a yellow screen, instead of following the common rule of becoming a green; that yellow in some shade is constantly perceived when a dark blue or a violet is employed—an impossibility under ordinary circumstances. Again when by voluntary effort on the part of the subject the aura has been changed in hue, the colours seen through the screens do not

These investigations confirm the view that a radical change in the visual apparatus is brought about by the dicyanin screens. In connection with the above experiments the following points should be particularly noted:—

1. The comparative ease with which the colours of the aura could be changed to blue or green.

2. The difficulty this subject experienced in producing a yellow, and the instability of the result.

During the examination of patients, several women, but no man, have been able to change the colours of their auras to a greater or less extent, some quite easily, who with a little practice could have given invaluable assistance. Most of these persons had an excitable temperament. Unfortunately all of them were unavailable for experimental purposes as none of them were artist's models.

The explanation of the aura is full of difficulties, some of which vanish immediately auto-luminosity has been conceded.

Elsewhere (page 51), it has been stated that the aura cannot be seen in complete darkness, and consequently is not self-luminous in the ordinary acceptation of the word. This statement requires qualification, and a criticism of the meaning of the term self-luminous. In general, the phrase "auto-luminous," denotes that an object can be seen in the dark through some inherent or acquired property of emitting rays roughly speaking between 7500λ, and 4000λ, the range of the ordinary visible solar spectrum. If, however, the substance emanates rays of say, 3500λ, which are usually quite invisible, it will be classed among the objects that are not self-luminous. If the human eye can by some means or other

be enabled to see these rays, then the substance would be defined as auto-luminous; consequently the term resolves itself into a physiological conception. Should these postulates be admitted, it seems easy to advance a step further, and to conceive that an object may emit rays which would be visible if they were in sufficient abundance to act as an effective stimulus. Since appropriate stimulation may render effective a stimulus otherwise subliminal, and such a result appears to have been obtained in the case under discussion, whatever the nature of the rays concerned, the aura may be conceived as being auto-luminous in this strictly limited sense.

The aura appears as a faint cloud whose structure and distribution is determined by forces emanating from the body and which becomes visible in a dim diffused light.

As soon as a certain change in the eye has been brought about by the use of dicyanin screens, the aura can be seen. It is suggested that the alteration is in the direction of retinal sensitisation to ultraviolet light.

The aura cannot be discerned in total darkness, therefore it either does not produce rays which can be recognized by the eye, or if it does they are not sufficiently abundant to cause effective stimulation.

TABLE IV

COLOUR OF AURAS EXAMINED WITH AND WITHOUT COLOURED SCREENS

	COLOUR OF AURA	RED SCREEN	ORANGE SCREEN	YELLOW SCREEN	GREEN SCREEN	BLUE SCREEN	VIOLET SCREEN
1	Blue with a little grey	0A. Carmine 1A. Carmine	Blue Warmer blue	Blue Darker blue	Blue Purple	Brilliant Orange	Purple Dark yellow
2	Reddish grey by voluntary effort	0A 1A	Mauve Mauve	Carmine Bluish red	Unable to tell the colour	Purple blue Orange	Violet Plum
3	Bright blue by voluntary effort	0A 1A	Blue Red	Orange Yellow Blue (Not combined)		Blue Blue	Plum Plum
4	Bluish grey	Plum	Reddish grey	Blue		Yellow ochre	Yellow
5	Bright blue by voluntary effort	Red Blue	Red Blue	Blue		Dirty yellow ochre	Ochre
6	Yellow by voluntary effort		Yellow with red tinge			Yellow	Yellow
7	Green by voluntary effort		Red	Ochre	Ochre	Ochre	Ochre
8	Very fine blue	Dull carmine The	Bluish grey inner aura the same—	Yellow only darker.	Green	Blue	Reddish blue
9	Very fine blue	Carmine	Blue	Yellow Blue	Blue	Blue	Bluish violet
10	Grey	Reddish grey	Grey Peculiar	Grey hardly grey			Ochre
11	Greenish grey	Reddish green	Greenish yellow	Greenish yellow	Yellow and peculiar blue	Yellow Green Blue	Purple
12	Blue with a little grey	Carmine Blue	Yellow Green	Green Yellow Blue	Grey? Yellow	Yellow Blue	Violet Green
13	Bluish green and white	Red Green	Red. Green (Opaque)	Green with a little blue	Green with a little blue	Green with a little blue	Blue
14	Peculiar blue	Reddish blue	Orange blue	Yellowish blue	Green	Yellow Blue	Blue

APPENDIX. CHAPTER IV

FROM the commencement of the recent calamitous war, it has been impossible to obtain any dicyanin, and at the present time the probability of a further supply seems to be very remote. It was formerly made in Germany, and the demand for it has always been limited, so that there does not appear to be any likelihood that the new dye works will attempt this particular compound until the more marketable colours have been produced to their full extent.

It is unreasonable to suppose that the properties attributed to dicyanin should be confined to a single dye, and probably others more or less efficient may be discovered amongst those that will be produced as soon as conditions become more settled. The necessary experiments must be made by other workers, as the author feels on account of age and growing infirmities unable to undertake them. He, however, thinks a few hints about the procedure may be useful.

First of all it is to be expected that a suitable dye will be found amongst those of a blue colour, and especially those which transmit the shorter wave lengths of the spectrum in the greatest abundance, with the least amount of the longer.

In the search of a suitable dye he would suggest the use of a microscope in a manner similar to that described on page 62, but the process may be considerably curtailed. Suppose the same microscopic power and the same object be employed, it would only be necessary to accurately focus a bristle of the blowfly's proboscis in ordinary daylight, using the coarse adjustment, which must not be altered again. For

the next step the observer should gaze at the light for from half to one minute through a screen containing a moderately dark solution of the dye to be tested. After this he should focus the bristle a second time with the fine adjustment. Should no alteration in the focus be required, probably the dye will prove useless for the purpose on hand, but should it be necessary to lower the objective towards the slide by two or more divisions on the wheel, then the dye may be practically tested by using it instead of dicyanin before looking at the aura. No further experiments should be carried out on the same day.

N.B.—It is extremely necessary that the plan mentioned on page 62 for obtaining the accuracy of the focus and eliminating the effects of accommodation should be strictly adhered to. A little practice makes this quite easy to perform.

Footnotes

64:* λ is the symbol for Angstrom's unit, viz., 10^-16 metre, or one-tenth millionth of a millimetre.

67:* +2.5 mi is the amount of adjustment required to bring the object into focus again in the white light after peering through the dicyanin screen.

73:* For the reason of choosing yellow instead of green see chapter vi. page 141.

Red	made with	a solution of	carmine. (The same as used for defining the inner aura.)
Orange	„	„	yolk yellow.
Yellow	„	„	K yellow.
Green	„	„	napthol green.
Blue	„	„	methylene blue.
Violet	„	„	gentian violet.

CHAPTER IV

OPTICAL PROBLEMS

TABLE III

TABLE IV

COLOUR OF AURAS EXAMINED WITH AND WITHOUT COLOURED SCREENS

APPENDIX. CHAPTER IV

Footnotes