Kilner and the human aura: a primer

Project: Walter J. Kilner, The Human Atmosphere, or the Aura Made Visible by the Aid of Chemical Screens (Rebman, New York and London, 1911). Kilner signs himself "B.A., M.B. Cantab., M.R.C.P., late Electrician at St. Thomas's Hospital, London" [read: PDF p.8].

Sources and their limits. The project folder holds one document, a Google Books scan of the 1911 book. Its text (OCR, text recognised by software from the page scans) is readable throughout, so there is no source gap for the book itself. Deep reads (a full, question-led reading of named pages) cover Chapters I-III's protocol and observer passages (PDF pp.20-108), Chapter IV (the afterimage method), Chapters V-VII (every diagnosis and prediction, PDF pp.166-325) and the Appendix (the "will" experiments). Three files the Investigator saved in research/files/ have also been deep-read since the first version of this primer: Kilner's 1920 second edition, Boddington's c.1931 booklet (a seller's account), and de Fontenay's report in the Annales des Sciences Psychiques (March 1912). Several things that bear on the verdicts are still unread: the British Medical Journal (BMJ) review of 6 January 1912 (the download was blocked), the New York Herald and New York Times reports of 1911 (known only through clippings quoted in the Annales), and the full table of Kilner's 1911-12 microscope paper in the Archives of the Roentgen Ray (read only by the Investigator, in a browser; the 1920 edition's version of the table is too garbled in the OCR to use). Where this primer leans on those, it says so.

Case numbers. The OCR of the 1911 book reads the digit 3 as 8 in case headings, so the heading printed "Case 18" over the dressmaker I. N. is really Case 13 (the genuine Case 18 is a 58-year-old bootmaker), "Case 28" is Case 23, and "Cases 80-89" are Cases 30-39; the book runs Cases 1-42 [read: page images, via arbiter 11.1]. This primer uses the corrected numbers. Case numbers also change between the 1911 and 1920 editions (the 1911 model, Case 42, is Case 25 in 1920).

Tags. [read] = from the book or a saved file; [web] = from the Internet, URL given; [memory] = from training, with confidence; [calc] = computed in example.py (run: .venv/bin/python review/Kilner-Walter/example.py). Page numbers are PDF scan pages ("PDF p.N"); the printed page number is the PDF page minus 19. Verdicts are the arbiter's (arbiter.md); this primer adds none.

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1. The idea in one paragraph

Walter Kilner was a London hospital physician in charge of electrical treatment. In his 1911 book he reported that if you first stare at daylight for a while through a thin glass cell filled with a blue coal-tar dye, dicyanin, and then look at an undressed person standing in dim, even light in front of a black background, you see a faint grey-blue haze around the body. He called it the aura and described three layers: a dark band next to the skin (the "Etheric Double"), a denser inner layer about three inches wide with fine streaks and occasional "rays", and a wider, misty outer layer. He believed it came from forces in the body acting on the ether, and that its width, shape and texture told you about a person's sex, age, temperament and health. He also invented a second trick: stare at a strip of coloured paper, then look at the patient, and the ghost image of the strip (an afterimage) lies across the body; Kilner held that the ghost turns lighter or darker over diseased or painful places, and could even be used to judge pregnancy or the approach of a period. Finally, he reported that a paid model could change her aura's colour by willing it, and that he could find the spot she was willing, without being told where, by using the ghost band. He sold the screens with the book, published his methods in detail, and reported some failures. Others tried the screens in 1911-12 with mixed results; no blinded test is on record.

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2. What you need to know first

2.1 Light, wavelength and the visible band. Light is an electromagnetic wave. Its wavelength λ (Greek "lambda", the distance between wave crests) sets its colour. The human eye responds to roughly λ = 380 to 740 nanometres (nm; 1 nm = 10⁻⁹ m): violet at the short end, red at the long end. Shorter than violet is ultraviolet (UV); longer than red is infrared (IR). The front of the eye (cornea and lens) absorbs almost all UV below about 390 nm, so UV never reaches the retina in a normal eye [web: https://pmc.ncbi.nlm.nih.gov/articles/PMC11826699/, via arbiter]. Read: E. Hecht, Optics (any edition), the chapters on electromagnetic waves and on the eye.

2.2 How the retina detects light. The retina has two kinds of light-sensitive cells. Cones work in bright light, give colour vision, and come in three types sensitive to short, middle and long wavelengths (often called "blue", "green" and "red" cones, though the long-wavelength one peaks in the yellow-green) [memory, high]. Rods work in dim light, are far more sensitive, and do not distinguish colour. Rods contain the pigment rhodopsin ("visual purple"), which is bleached by light and slowly rebuilt in the dark. Adapting to the dark takes 20 to 30 minutes [memory, high]. Read: E. B. Goldstein, Sensation and Perception (any edition), chapters on the receptors and on dark adaptation; or B. Wandell, Foundations of Vision.

2.3 The Purkinje shift. In daylight the eye is most sensitive near 555 nm (yellow-green). In dim light, when rods take over, the peak moves to about 507 nm (blue-green). So in twilight reds look darker and blues look relatively brighter [memory, high]. Kilner knew this and described it correctly (section 3.2).

2.4 Filters and absorption. A coloured filter (a glass cell of dye solution, a gel) works by absorbing some wavelengths and passing the rest. The fraction passed, the transmittance T, obeys the Beer-Lambert law (below), and T is never greater than 1. A filter can remove light; it cannot add light of a wavelength that was not there. Read: Hecht, Optics, the sections on absorption.

2.5 Afterimages and colour adaptation. Stare at a bright yellow patch for 30 to 60 seconds and then look at a white wall: you see a bluish ghost of the patch. The receptors that responded strongly to yellow have temporarily lost sensitivity (they are "adapted" or "fatigued"), so where you look, the white wall's light is reported mostly by the receptors that were not tired. That is a negative afterimage. It exists only in the observer's visual system and moves wherever you look. Its apparent brightness and colour depend on the surface it falls on: on a darker or differently coloured surface it looks darker or different [memory, high]. The broader effect, where an overall tint resets the eye's colour balance for a minute or more, is called chromatic adaptation. The theory that colours are coded in opposing pairs (red against green, blue against yellow) is opponent-process theory (Hering), which sits alongside the three-cone (Young-Helmholtz) theory [memory, high]. Read: T. N. Cornsweet, Visual Perception (1970); Goldstein, chapters on colour.

2.6 Things the eye adds that are not in the scene. Three are central here [memory, high]: - Mach bands: next to a sharp edge between light and dark the eye sees an extra-light stripe on the light side and an extra-dark stripe on the dark side. They come from lateral inhibition, the way neighbouring retinal cells damp each other. - Veiling glare: light scatters inside the eye, so any bright object on a black ground carries a faint halo. - Troxler fading and filling-in: a faint, steady pattern held still in the visual field fades and comes back; the brain fills gaps. Read: Cornsweet, Visual Perception (Mach bands, lateral inhibition).

2.7 Lenses, dioptres and the microscope. A thin lens of focal length f forms an image of an object at distance s at a distance s′ given by 1/s + 1/s′ = 1/f. Opticians measure the "power" of a lens, or the curvature of a wavefront, in dioptres (D): 1 D is the reciprocal of 1 metre. The wavefront curvature is called vergence, V = 1/distance to the point the light comes from or goes to. The eye's lens can add up to about 10 to 15 D of power in a young adult by changing shape (accommodation), falling to about 1 D by age 60 [memory, high]. A compound microscope has an objective (makes an enlarged image inside the tube) and an eyepiece (acts as a magnifying glass on that image). Read: Hecht, Optics, the geometrical optics chapters; D. Atchison and G. Smith, Optics of the Human Eye.

2.8 Scattering and visibility. A haze is visible because tiny particles scatter light toward you. Clean air scatters weakly (Rayleigh scattering, strongest for blue light, which is why the sky is blue); mist and smoke scatter strongly. Read: C. Bohren, Clouds in a Glass of Beer (popular and exact); C. Bohren and E. Clothiaux, Fundamentals of Atmospheric Radiation.

2.9 Testing a perception-based claim. When the measuring instrument is a person's judgement of "lighter or darker", the result can be changed by what the person expects. The standard protections are: a control condition (nothing there, or a decoy), blinding (the judge does not know which condition is which), several independent judges, many trials, and the hit and miss counts reported in full. The chance of a hit by luck is worked out from the size of the target and the area searched. Read: D. Freedman, R. Pisani and R. Purves, Statistics; J. Taylor, An Introduction to Error Analysis.

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3. The textbook view

3.1 Light and the eye

Photon energy and wavelength are related by

E = hc/λ,

where E is the energy of one photon, h = 6.63×10⁻³⁴ J·s is Planck's constant, c = 3.00×10⁸ m/s is the speed of light, and λ is the wavelength. Violet light at 400 nm carries about 3.1 electron-volts (eV) per photon, red at 700 nm about 1.8 eV. A normal eye sees roughly 380-740 nm. People who have had the lens removed (without a UV-blocking implant) can see somewhat into the near UV, because the retina itself responds there [memory, high]. That fact matters for fairness to Kilner: the idea that the visible band has "soft" edges that depend on the eye is not absurd. But in a normal eye the lens is the barrier, and no screen held in front of the eye removes the lens.

3.2 What Kilner got right about the eye

Kilner's own account of dark adaptation reads [read: PDF p.128-129]:

"As soon as the retina has become accustomed to the dim light, the red end is less apparent, while the maximum intensity is removed to the green, and the blue end becomes brighter. This corresponds to the change seen in the visual purple."

That is the Purkinje shift, described accurately, with the right pigment (rhodopsin). He also states the three-receptor theory of colour vision [read: PDF p.135, via deep read], describes chromatic adaptation by a sound demonstration (a faint carmine band projected by a magic lantern is seen more or less plainly after looking through a blue or red glass) [read: PDF p.137-138, via deep read], and says plainly that "the complementary colours are entirely subjective" [read: PDF p.140]. He then proposes that the dicyanin screen acts on the visual purple, "either increased in quantity, or altered in quality", and labels the rest of his explanation "completely hypothetical and without proof" [read: PDF p.131]. So his starting points are real physiology, and he was candid about where he went beyond them.

3.3 What a filter can do

For light passing through a dye solution of concentration c (moles per litre) and path length ℓ (cm), with molar absorption coefficient ε(λ) (litres per mole per cm, depending on wavelength),

T(λ) = I_out/I_in = 10^(−ε(λ)·c·ℓ), so 0 ≤ T ≤ 1.

Kilner looked at daylight through his screen with a pocket spectroscope and found that "the orange is entirely and the yellow is to a great extent obliterated. The red is unaltered, and the blue and violet slightly diminished" [read: PDF p.131]. That is exactly what a filter does: it subtracts. Looking at bright light through it for a minute tires the eye's receptors unevenly (less light reached the cones that respond to orange-yellow, more to red and blue), so for a while afterwards the eye's colour balance and its state of adaptation are changed. That is the only route by which the screen can change what is seen next: through the observer's eye, not through the subject.

3.4 The afterimage as a multiplier

A simple model of adaptation (von Kries adaptation [memory, high]) says each cone class i responds with a signal

R_i = g_i · L_i,

where L_i is the light from the surface that class i absorbs and g_i is that class's gain (sensitivity). Staring at a yellow strip lowers the gains of the long- and middle-wavelength cones in one strip-shaped patch of retina. When you then look at a patient, that patch reports every surface with those gains lowered: a bluish ghost band. Two consequences follow directly from the formula: - the ghost's apparent shade on any spot depends on L_i at that spot, i.e. on the colour and brightness of the skin, shadow, sweat sheen or background there; and - it depends on g_i, which recovers with time, varies across the retina, and is disturbed by small eye movements.

Kilner records both kinds of effect himself: eye movement "completely destroying the benefit of the observation" [read: PDF p.144, via deep read], colours drifting to purple and vanishing [read: PDF p.139-140, via deep read], and the ghost blending with the background tint [read: PDF p.140, via deep read].

3.5 Real physical "auras" round a body

Two are known and measurable [memory, high, except where tagged]: - Thermal radiation. A body at T ≈ 310 K emits infrared with a peak wavelength from Wien's law, λ_max = b/T, with b = 2.898×10⁻³ m·K, giving λ_max ≈ 9.3 µm (micrometres): far infrared, invisible. - A warm air layer. Air next to warm skin rises in a thin convective layer. Its refractive index n differs from the room's by Δn ≈ (n − 1)·ΔT/T ≈ 2.9×10⁻⁴ × 10/300 ≈ 1×10⁻⁵ (n − 1 is the refractivity of air, ΔT the temperature excess, T the absolute temperature) [calc: Physicist, checked by arbiter]. This is invisible to the eye, but schlieren photography (an optical method that turns small refractive-index gradients into brightness) images it routinely. De Fontenay raised such "ordinary" auras in 1912 [web: Annales des Sciences Psychiques 22 (1912), via Investigator].

The body also gives off an extremely faint light ("ultra-weak photon emission"), far too weak to see [memory, medium; not web-checked; no verdict depends on it].

3.6 How visible a scattering haze would have to be

Kilner says the aura is not luminous (it was "searched for constantly in the dark without the slightest sign") and is seen by "reflection of light from some extraneous source" [read: PDF p.109]. So it would have to scatter light. A thin scattering layer of optical depth τ (the fraction of light scattered while crossing it, for small τ) in front of a black cloth of reflectance ρ ≈ 0.03 adds a contrast of roughly C ≈ τ/(4ρ) for isotropic scattering. To reach a just-visible contrast C ≈ 0.02 needs τ ≈ 4Cρ ≈ 2.4×10⁻³. Over a layer 0.25 m thick that is a scattering coefficient σ ≈ 1×10⁻² per metre, about 740 times clean air (1.3×10⁻⁵ per metre). Koschmieder's rule for visibility distance, V = 3.9/σ, gives V ≈ 0.4 km: as hazy as a light mist [calc: arbiter, correcting the Mathematician by a factor of 4]. Kilner himself says the aura does not move with draughts or warm air [read: PDF p.110-111], i.e. it does not behave like a mist. This bound tests nothing on its own; it shows that a reflecting haze bright enough to see would be a lot of matter.

3.7 The ether

The "luminiferous ether" was the supposed medium that carried light waves. The Michelson-Morley experiment (1887) found no sign of motion through it, and Einstein's special relativity (1905) made it unnecessary [memory, high]. In 1911 many physicists still used the word, so Kilner's "force acting on the ether" was a period phrase, not an eccentric one. It has no content in modern physics.

3.8 Uranyl salts glow

Uranyl compounds (such as uranyl nitrate, the "uranium nitrate" Kilner used) absorb violet and near-UV light (about 350-500 nm) and fluoresce green-yellow (about 500-600 nm) [web: https://en.wikipedia.org/wiki/Uranyl_nitrate, via arbiter]. Daylight contains that violet and near-UV. So a faint yellow glow round a uranyl crystal is real physics, and needs no radioactivity.

3.9 The N-ray lesson

In 1903 René Blondlot, a respected physicist at Nancy, reported "N rays", detected by small changes in the brightness of a faint spark or phosphorescent screen judged by eye. In 1904 the American physicist R. W. Wood secretly removed an essential prism from the apparatus; Blondlot's team still reported the effects [web: https://en.wikipedia.org/wiki/N_ray]. The case is the textbook example of observers at the threshold of perception seeing what they expect. Kilner had worked on N-rays before the aura (see section 4) [read: PDF p.120-121, via arbiter]. (See also the Blondlot primer in this review series.)

3.10 Night myopia

In dim light the relaxed eye becomes slightly short-sighted, typically by 0.5 to 1.5 D, because accommodation drifts to a resting "dark focus", the dilated pupil admits more of the lens's spherical aberration, and the Purkinje shift moves vision toward blue light, which the eye focuses more strongly [memory, high]. This is relevant to Kilner's report of a "temporary myopia" after using the screen (section 5).

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4. Where Kilner departs

The single most important point of departure is the second row of the C.C. (afterimage) entry: Kilner knew the afterimage is "entirely subjective", described the observer-side effects himself, and then built a diagnostic method whose list of causes contains only properties of the patient. Everything downstream (diagnosis, aura colour, willed colour) inherits that choice.

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5. Worked example: how big a change in the eye is Kilner's microscope shift?

Kilner's one quantitative, multi-observer measurement is a microscope test, first published as "The Shifting of the Chromatic Focus of the Eye by the Use of a Dicyanin Screen" (Archives of the Roentgen Ray 16, 1911-12, pp.344-352) [web: https://babel.hathitrust.org/cgi/pt?id=uc1.d0010345536&seq=360, read by the Investigator in a browser; the full table was not saved] and repeated in the 1920 second edition [read: 1920 p.59-70]. The method, from the 1920 text: a microscope whose fine adjustment moves 1/100 inch per turn, the wheel divided into ten, so one division, which Kilner calls a "mi" (mille-inch), is 1/1000 inch; "the lowest eyepiece, inch-and-a-half objective"; a blow-fly bristle as target; glass cells of weak red, yellow, blue and violet dyes as colour screens. The observer focuses in white light, then refocuses with the fine screw alone through each screen; then looks at the light through the dark dicyanin screen for about 30 seconds and repeats the series [read: 1920 p.61-62]. Observer A, before dicyanin: red −1, blue +1, violet +3 mi. After dicyanin: white +2.5 mi, then red +1, yellow +1, blue +2, violet +3.5 mi; "tested on three separate occasions, and the readings obtained showed no variations" [read: 1920 p.62-63]. Across the observers the white-light shift ran from +1 to +6.5 mi, largest in a clairvoyant, smallest in observers over 60 [web, via Investigator; read: 1920 p.65-66]. Kilner reads this as the eye's focus for colours sliding toward violet, and from there toward the ultraviolet.

Kilner also built in a real control: during each series he secretly disturbed the focus two or three times and rejected the series unless the observer came back to the same readings; "not more than one series out of every three or four" passed, leaving fifty [read: 1920 p.63]. That selects steady observers, and it also means roughly 150 to 200 series were run and 100 to 150 are not reported.

Where the idea came from: Kilner noticed that after years of "constant peering through the dicyanin screen" his opera glasses needed less extension and his reading distance had shortened; a medical friend reported a man who needed no reading glasses for over 24 hours after being shown the aura; "every person who has remarked upon his or her sight being temporarily improved, was presbyopic" (long-sighted with age), and the effect was never noticed in normal or short-sighted eyes [read: 1920 p.60-61]. The Archives editorial called it "a sort of artificial or temporary myopia" [web: via Investigator, research/2026-10-04-hathitrust.md].

The question: if the eye itself changed, how many dioptres would Observer A's 2.5 mi be? example.py does every step; the numbers below are its output [calc].

Step 1: units. 1 mi = 1/1000 in = 25.4 µm (micrometres). Observer A's 2.5 mi = 63.5 µm; the largest shift, 6.5 mi = 165 µm.

Step 2: the objective multiplies a focus shift by M². Start from the thin-lens equation 1/s + 1/s′ = 1/f. Differentiate with respect to the object distance s:

−ds/s² − ds′/s′² = 0 ⇒ ds′/ds = −(s′/s)² = −M²,

where M = s′/s is the lateral magnification (how much bigger the image is than the object). So moving the stage by Δz moves the image inside the tube by M²·Δz. This "longitudinal magnification" is why a microscope's focus is so touchy. A 1.5-inch objective has a focal length of 38 mm; M is roughly the tube length divided by that: about 4.2 on a 160 mm tube, about 6.7 on the English 10-inch (254 mm) tube of the period [assumption; memory, medium].

Step 3: the eyepiece turns an image shift into a vergence change. Use Newton's form of the lens equation, x·x′ = −f_e², where x and x′ are measured from the eyepiece's front and back focal points and f_e is its focal length. When the tube image sits in the eyepiece's front focal plane (x = 0) the light comes out parallel and a relaxed normal eye sees it sharp. Shift the tube image by x: the eyepiece's image is now at x′ = −f_e²/x from its back focal point, where the eye roughly sits, so the light reaching the eye has vergence

V = 1/x′ = −x/f_e², i.e. |ΔV| = Δx/f_e².

Step 4: put them together. If the observer's eye changes its focusing by ΔR dioptres, the observer must move the stage until the light's vergence changes by the same amount:

ΔR = M²·Δz / f_e².

Per mi (Δz = 25.4 µm), with the 1.5-inch objective:

Check the third row by hand: M²/f_e² = 6.7²/(0.05 m)² = 44.9/0.0025 = 1.80×10⁴ D per metre; times 25.4×10⁻⁶ m gives 0.46 D.

Step 5: calibrate with Kilner's own numbers. We do not know the eyepiece, so use Observer A's colour readings before dicyanin. His red-to-violet spread is 4 mi. The eye's own focus difference between red and violet light (its longitudinal chromatic aberration) is about 2 D [memory, high]. If the whole 4 mi spread is the eye's, the scale is 2 D / 4 mi = 0.5 D per mi, in the middle of the Step 4 range. (If part of the spread came from the objective's own colour error, the eye's share would be fewer mi and the scale per mi a little larger.) At 0.5 D per mi: - Observer A's dicyanin shift, 2.5 mi ≈ 1.25 D, "about 1 D" (range 0.4 to 4.6 D over the Step 4 instruments); - the smallest shift, 1 mi ≈ 0.5 D; the largest (the clairvoyant), 6.5 mi ≈ 3.3 D.

Step 6: compare with ordinary changes of the eye's focus. At 0.5 D per mi, typical night myopia (about 1 D, section 3.10) is 2 mi; the whole accommodation range left at age 60 (about 1 D) is 2 mi; at age 40 (about 4 D) it is 8 mi [calc; eye figures memory, high]. Kilner's shifts, 1 to 6.5 mi, sit squarely in this range.

Step 7: the microscope's depth of focus is the wrong yardstick. A microscope's diffraction depth of focus is about λ/NA², where NA (numerical aperture) is the sine of the half-angle of the cone of light the objective accepts. A low-power 1.5-inch objective of the period had NA of roughly 0.06 to 0.1 [memory, medium], so λ/NA² with λ = 0.55 µm is 55 to 153 µm, i.e. 2 to 6 mi. That looks as large as the shifts themselves, but an observer setting best focus repeats to a fraction of this depth. The right yardstick is how much one observer's settings scatter with no screen at all, and Kilner reports no such figure, only that rejected series were thrown out.

What the numbers say. 1. The size is plausible. A shift of about 1 D is the size of ordinary changes in an eye's focus after staring at a bright light through a dark filter: accommodation drifting toward its resting "dark focus", a larger pupil, a change in where the observer judges best focus [memory, medium]. The arbiter's verdict on the focus shift is Plausible, untested by neutral observers. It matches the anecdotes: a temporary myopic shift of about 1 D is just what would help a mild presbyope read without glasses for a while. One reported pattern also fits accommodation: the observers over 60, who have little accommodation left, showed the smallest shifts. 2. It does not show ultraviolet sight. A focus shift measured in visible light says nothing by itself about whether the eye can now see ultraviolet; the lens still absorbs below about 390 nm (section 2.1). Kilner draws the line himself: "no test has been devised, the question must be treated entirely theoretically" [read: 1920 p.68]. His step to "an ultra-violet phenomenon" is Never properly tested (arbiter). 3. A reported correlation without numbers. Kilner says that whenever the white-light shift after dicyanin exceeded the shift from the blue screen alone, the observer had "not the slightest difficulty in seeing the aura" [read: 1920 p.63-64], and he proposes this as a quick screening test. No counts are given. 4. A lesson in assumptions. The first version of this primer, and the first pass of the reviews, assumed a 1/4-inch objective (the Investigator's note of the 1911-12 paper reads "1/4-in [OCR '14-inch']"). That gives M ≈ 25 to 40, about 6 to 65 D per mi, and the conclusion that the shift was "far too large to be a change of the eye's optics". The 1920 text says "inch-and-a-half", and "14-inch" is most likely an OCR misreading of "1½-inch"; the arbiter withdrew the earlier conclusion (arbiter 11.3). Because the answer scales as M², a factor of 6 in the objective changes it by a factor of about 40. Always ask which instrument the number came from. 5. Fair to Kilner: he turned a perceptual claim into a number on an instrument, with many observers, a secret-displacement control, and a named dye. What is missing is the scatter of repeated settings, the rejected series and a sham-dye comparison. 6. A seller's claim that runs the other way. Boddington's booklet carries the heading "Dicyanine cures short sight" [read: Boddington p.18]. A temporary myopic shift would make a short-sighted eye worse, not better, and Kilner reported no effect in myopia [read: 1920 p.61].

The cheap modern test (arbiter): measure each observer's refraction with an autorefractor (an instrument that measures the eye's focusing error) before and after the 30-second dicyanin routine, with a methylene-blue screen as the sham.

Three smaller checks you can do yourself (also in example.py)

(a) The hidden-site trials (Appendix, Experiments 5 and 6). The model willed a red spot "not exceeding an inch in diameter, somewhere or other upon the abdomen"; Kilner searched with the blue afterimage band and put his finger on "the exact centre"; in a second trial (yellow, somewhere on the thorax) his finger was "about half an inch from the true centre" [read: PDF p.337-338, via deep read]. If one random point is chosen in an area A, the chance of landing within r of the target is πr²/A. For an abdomen of 30 × 25 cm (A = 750 cm²) and r = 2.5 cm: 2.6%; for r = 0.5 in (1.27 cm): 0.7% [calc]. But Kilner was not choosing one random point: he scanned a field that, by his own account, often shows small dark patches, so picking among, say, five candidate patches multiplies the chance about fivefold (3% to 13%). The model could see auras herself, told him when to look, and was in his view; no sham trials were run; and "No more experiments of this nature were possible" [read: PDF p.338, via deep read]. The 1920 edition reprints the two trials unchanged and adds that the model "signalled readiness" and Kilner "was not told" the position [read: 1920 p.125, via arbiter]. The arbiter's reading: about 1% to 3% per trial for one blind guess, unknown and probably several times larger for the procedure used; two trials allow no statistical conclusion.

(b) The heredity tables. The arbiter read Kilner's Tables I and II from page images [read: PDF p.80-81, via arbiter] and classed each aura W (wide), A (average) or N (narrow). Parent-child pairs: 15 of 15 in the same class. Using the pooled class frequencies (A 24, W 15, N 9 of 48), two unrelated people share a class with probability (24² + 15² + 9²)/48² = 0.383, so 15 of 15 by chance is 0.383¹⁵ ≈ 6×10⁻⁷ [calc].

The sibling count depends on what you count. Table II lists 9 brother-sister pairs, 5 concordant. The QE found that Table I also contains sibling sets: X.X., B.X. and C. (all narrow; 3 pairs, though only 2 independent comparisons) and K.M. and M.M. (both average; 1 pair). The X family's three "Granddaughters" F.X., G.X. and E.X. (narrow, average, wide) are sisters or cousins, 0 of 3 concordant. The one-sided Fisher exact test asks how likely it is, if parent-child and sibling pairs agreed equally often, that all the disagreements would fall among the siblings; with parent-child at 15 of 15 and siblings at k of n it is C(n, n−k)/C(15+n, n−k) [calc]:

Pairs share members (the Table I siblings match each other partly because each matches the same parent), so these p-values are indicative only. What they show: parents and children agree far above chance; siblings agree somewhere between "not unusual" and "mildly above chance", depending on the counting. The first version of this primer said siblings "do not agree beyond chance" and that "the asymmetry favours a method effect over inheritance"; the arbiter has withdrawn both statements (arbiter 11.4). Two ordinary explanations remain open and neither is excluded: a family resemblance of build and health (Table I's narrow group is mostly one diseased family plus neurotic, epileptic and kidney patients), or an unblinded classifier who knew the relationships and diagnoses. Kilner says the tables contain "all the examples which have been investigated" [read: PDF p.79-80] and he printed the discordant siblings, which argues against cherry-picking; but his width classes were fixed "by experience only, and not by any scientific plan" [read: PDF p.78-79], and one parent (N.N., footnote 1) was classed after the fact; without her the result is 14 of 14. The tables are a real dataset worth a blind repeat.

(c) The colour series of the first hundred cases. The heredity tables are not the only counts in the book. Kilner classified the aura colour of "the first hundred cases inspected" [read: PDF p.247-248]: blue 40 ("no individual below ... the average in mental power"); blue with grey 36 (1 hemiplegia, 2 epileptics, 1 meningitis); grey 17 (6 epileptics, 2 eccentric, 1 general paralysis, 3 mentally dull); not recorded 7. He calls the table "conclusive". All 8 epileptics fall outside the blue group. If 8 cases were placed at random among the 93 with a recorded colour, the chance that none lands among the 40 blue ones is C(53,8)/C(93,8) = 0.009; counting the 7 unrecorded as non-blue, C(60,8)/C(100,8) = 0.014 [calc]. What the number cannot say: the epileptics came as known epileptics, the classifier knew it, "grey" is the observer's own judgement, and "mental power" has no stated criterion. Kilner also admits that the prepared eye makes it "impossible to appreciate any great variation in range of colour" [read: via arbiter 11.5]. A definite scheme with published counts is exactly what a blind repeat could test, which is why the arbiter now rates this part "Never properly tested" rather than "Not testable as stated".

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6. Evidence table

Verdicts are the arbiter's final ones, including its QE revision (arbiter.md section 11, which governs where it differs from the first pass).

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7. What a learner should take away

What is solid. - The afterimage is real, is made in the observer's eye, and its apparent shade depends on the surface it lands on. Kilner's C.C. band is a real visual effect; the open question is only what it is reporting. - Kilner's physiology was good for 1911: he described the Purkinje shift and rhodopsin correctly, accepted the three-receptor theory, and demonstrated chromatic adaptation. His idea that a prepared eye sees differently is true; adaptation does change what faint, low-contrast things look like. - Some people, in several places, did see a haze after the screen routine. That is consistent with known vision effects and is the arbiter's "weak form". The 1920 methylene-blue mix-up suggests the dicyanin screen matters and that expectation alone was not enough for that one viewer, though methylene blue passes different colours, so any theory expects a difference. - The microscope focus shift, about 1 D on the instrument Kilner names, is the right size for an ordinary change in the eye's focus, and it fits his presbyopic readers. It is a cheap, testable effect (section 5). - He reported failures (photography; the willed colour never matched the cue book; the yellow "never became a true yellow"; the C.C. band's silence in epilepsy, hysteria and kidney disease), warned that "enthusiasm and imagination are wont to lead experimenters astray" [read: PDF p.22], named his dye, published corrections in 1920 (a retracted "healthy symmetric" case; the bromine dose; the duration of enlargement), and described his methods well enough for others to try. The turn-round control and the secret focus-displacement control are real controls. - Real physical things do surround a body: an infrared glow and a warm air layer visible by schlieren methods. A yellow glow round a uranyl crystal is real fluorescence.

What is wrong, and why it is instructive. - A filter cannot add what is not there. A dye screen can only change the observer, so every effect of the screen is first a claim about the observer's eye. Kilner half-saw this (he credits the screen's action on the retina for the aura's blue colour [read: PDF p.157]) but did not draw the consequence. - A list of causes that leaves out the instrument. His four causes of a changed afterimage band are all in the patient; the instrument (his own retina, his expectation) is not on the list, though he describes its faults. - A visible-light measurement used for an ultraviolet conclusion. The focus shift is measured with visible light and says nothing by itself about ultraviolet. Kilner admits no test had been devised. - Rules that cannot lose. Same change in all bands: texture. Opposite changes: colour. No change: texture "at times has no effect". Light spot: a gap. Dark spot: a small gap or dense surroundings. Every possible observation has an assigned cause. A method that cannot fail cannot tell you anything. - Elimination plus a circular witness. The aura-colour hypothesis is adopted because it "will explain all the remaining cases", with clairvoyants' testimony as support. Both moves assume what they set out to show. - The N-ray pattern. Faint, threshold-level judgements by an observer who holds the hypothesis, without blinding, are the classic route to false positives. Kilner had worked on N-rays first. The Archives review of the book made the same point in 1911: in "slight impressions it is difficult to distinguish ... between sight and suggestion" [web: via Investigator, research/2026-10-04-hathitrust.md]. - The experiment tests something other than the claim. The two hidden-site trials test location, not colour, because the blue band darkens for red and yellow alike. - Your own assumptions are part of the calculation. The first version of the worked example assumed the wrong objective and reached the wrong conclusion by a factor of about 40 (section 5, point 4).

The strongest items for claim 4, with their limits. The readings that went against what the patient said or believed are the ones that most weaken the obvious objection, that the patient cued the observer. The arbiter counts about four: the 38-year-old woman (period a week earlier than she expected, as Kilner foretold), Case 21 (pregnancy ruled out against her belief, period 7 days later), the young woman (no darkening when she expected her period, and it came late), and Case 34 (the cervical patch she denied, which her mother confirmed). Add the readings made without the history: Case 17, Dr Merrick's test case and the woman with back pain. Their limits keep the verdict at "Never properly tested": one observer, usually the treating physician; the outcome usually rests on the patient's own later recollection, as recorded by Kilner (the 38-year-old's hit comes from her account two months later, against Kilner's own note of a miss); and there are no denominators, so nobody can say how often a reading of that precision would be right by luck (the arbiter puts a single "about a week" call at roughly 10-15% on a 28-day cycle [calc: arbiter]) or how many readings failed unreported.

What is genuinely open. - Does a dicyanin-primed observer, blind, see more haze round a person than round a warm towel or an empty background, and more than with a sham filter of similar colour? H. C. S. said the towel was stronger; Kilner denied any haze round inanimate objects. Nobody has measured it. De Fontenay's 1912 designs (hidden magnets; a remote-switched wire board) were never run. - What did the BMJ reviewers actually do in 1911-12, and what did O'Donnell do in Chicago? The primary texts have not been read. - Does the dicyanin focus shift exceed the scatter of one observer's repeated settings, and does it survive a sham-dye comparison? An autorefractor would answer this in an afternoon. - Parent-child aura classes agree 15 of 15; siblings agree 5 of 9 to 9 of 13 depending on counting. Is that heredity, family health, or a classifier who knew the families? A blind classifier could answer it cheaply. The same goes for left-sided narrowing in epilepsy and for the colour series. - Do the 1920 fumigation colours survive a test where an assistant picks the gas and the side, using colourless gases as well? - Why the record goes dark after 1912-1920. A hospital physician publishes case lists and sells screens, and then there are no hospital trials, no follow-up papers, no student. The arbiter sets out the competing explanations: - Wartime loss of the German-made dye. Now stated by Kilner himself: "From the commencement of the recent calamitous war, it has been impossible to obtain any dicyanin ... formerly made in Germany", and further work "must be made by other workers", as he felt unable "on account of age and growing infirmities" [read: 1920 p.82-83, preface]. Boddington (a seller) says the same. Against: dicyanin was made and used as a photographic sensitiser in 1918-19 (US Bureau of Standards), substitutes later worked for Boddington and Bagnall, and Kilner himself proposed how others could find a substitute. - Age and death. Kilner died in June 1920 (Wikipedia); the 1920 preface speaks of "age with its attendant infirmities". The edition is dated September 1920, after his death. - Professional rejection. The BMJ "Macbeth's dagger" review; Boddington's report that the chemist who supplied his dye wished to stay anonymous for his "professional reputation" (one seller's account, and still evidence that pressure was felt). - Imitation screens. Boddington says expensive genuine screens "led to unscrupulous imitation by coloured water and glasses that were quite useless and brought such discredit on the doctor's work that it was finally dismissed as being due to 'suggestibility'" [read: Boddington p.15]. A seller's account that also promotes his own product; Kilner's own methylene-blue substitutions were inert, which fits. - Commercial failure. Screens at 17s. 6d. But the 1920 edition had a "Second Impression, May 1926" [read: 1920 title page], so the book was still in demand six years after his death; the first pass's "no sign of continued sales" was wrong. - Failure of others to see a reproducible effect (Paris). - A cold trail. Boddington says that by about 1929 "nobody could give any definite information" about the screens and that most writers on them "had never seen one" [read: Boddington p.15]. No evidence of blocked publication or confiscation was found. The records that would decide are the BMJ review text, St Thomas's Hospital minutes, Hoechst/Meister Lucius dye catalogues of 1910-20, Rebman's and Kegan Paul's sales, the Daily Chronicle of 14 March 1930, and Kilner's obituary and probate. These explanations are not exclusive, and the record does not yet decide between them.

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8. Check yourself

1. Kilner's spectroscope showed that his dicyanin screen removes orange and most yellow and dims blue and violet slightly. Using the Beer-Lambert law, explain why the screen cannot make a person's aura brighter, and say what it can change.
2. Kilner turned the patient round and found that the darker side of the afterimage band moved with the body. Which explanations does this rule out, and which does it leave in?
3. In the worked example, show that with a 1.5-inch objective on a 254 mm tube (M ≈ 6.7) and a 50 mm eyepiece one mi of stage travel is about 0.46 D at the eye. Then use Observer A's own red-to-violet spread (4 mi for about 2 D) to convert his 2.5 mi dicyanin shift into dioptres, and say whether that is a large change for an eye.
4. In Experiment 5 the model willed a red spot and Kilner found it with the blue band. Using Kilner's own prediction rules, explain why this trial cannot tell a red spot from a yellow one.
5. Design the cheapest experiment that would test whether the dicyanin screen lets people see something real round a human body. Name the control condition, the blinding and what you would count.

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9. Further reading

Mainstream. - E. Hecht, Optics (Addison-Wesley/Pearson, any edition): geometrical optics, lenses, absorption. - D. A. Atchison and G. Smith, Optics of the Human Eye (Butterworth-Heinemann, 2000): accommodation, chromatic aberration of the eye, night myopia. - T. N. Cornsweet, Visual Perception (Academic Press, 1970): adaptation, afterimages, Mach bands, lateral inhibition. - E. B. Goldstein, Sensation and Perception (any edition): receptors, dark adaptation, colour vision, opponent process. - B. Wandell, Foundations of Vision (Sinauer, 1995). - C. F. Bohren, Clouds in a Glass of Beer (Wiley, 1987): scattering and visibility in plain language. - G. S. Settles, Schlieren and Shadowgraph Techniques (Springer, 2001): how the warm-air layer round a body is imaged. - R. Rosenthal, Experimenter Effects in Behavioral Research (1966): how expectation shapes judgement data [memory, high]. - The N-ray story: R. W. Wood, "The n-Rays", Nature 70 (1904) 530-531 [memory, medium]; summary at https://en.wikipedia.org/wiki/N_ray. See also the Blondlot primer in this review.

Kilner and his period. - W. J. Kilner, The Human Atmosphere, or the Aura Made Visible by the Aid of Chemical Screens (Rebman, 1911): the project document. Read Chapter III (the screens and the eye), Chapter IV (the afterimage band), Chapters V-VII for the cases (especially the menstrual readings at PDF pp.253-254, Cases 16-17 on epilepsy, Case 21 at pp.317-318, Case 37 at pp.295-296) and the Appendix (Cases 41-42). - W. J. Kilner, The Human Atmosphere (The Aura), 2nd ed. (Kegan Paul, September 1920; second impression May 1926); OCR saved in research/files/. New in this edition: "an ultra-violet phenomenon"; the microscope focus experiments (pp.59-70); the methylene-blue mix-up (p.58); the Wimshurst charging experiments of 1915-1918, including the June 1915 repeat on the artist's model (pp.50-51, 91-102); fumigation with iodine, bromine and chlorine (pp.109-118); the hypnosis series with Dr A. Douglas (pp.126-133); the statement that "some women have the power of changing the colours of their auras by voluntary effort (no man or boy has as yet been found to possess this faculty)" (preface); Kilner's own account of the wartime loss of dicyanin (pp.82-83). - W. J. Kilner, "The Shifting of the Chromatic Focus of the Eye by the Use of a Dicyanin Screen", Archives of the Roentgen Ray 16 (1911-12) 344-352 [web: https://babel.hathitrust.org/cgi/pt?id=uc1.d0010345536&seq=360]. The same volume has Rebman's review (p.156), with its own caution about distinguishing "between sight and suggestion", the H. C. S. letter (pp.199-200) and Kilner's reply (p.240). Rebman published the book and sold the screens. - Review of The Human Atmosphere, British Medical Journal, 6 Jan 1912, issue 2662, pp.20-22 (PMC2344221): not yet read. - G. de Fontenay, "L'Aura humaine et les écrans du Dr Walter J. Kilner", Annales des Sciences Psychiques 22 (March 1912), printed pp.74-84 (saved in research/files/): the Paris trials and the two blind tests he proposed; the same volume (printed p.183) relays Werner and Caan's report of a weak "photo-activity" of human tissue, a different effect, no data given. De Rochas in vol. 21 (1911) 264-268, on the Chicago report. - F. Feerhow, Die menschliche Aura und ihre experimentelle Erforschung (Max Altmann, Leipzig, 1913), chapter III for Surya's Graz trials. - H. Boddington (ed. D. Gow), Aura. Kilner Screens (Aurospecs) and All About Them, London Psychic Educational Centre, Handbook No. 4 (c.1931) [web: https://archive.org/details/aurakilnerscreen00bodd; saved in research/files/]. Boddington sold "Aurospecs" goggles, so everything in it is a seller's account. It reports that Dr Drysdale Anderson bought Aurospecs in 1929 and that a Daily Chronicle article of 14 March 1930 "confirmed Dr. Kilner's researches" (the article is not quoted and has not been read); prints a foreword by A. E. Mundy, who says he compounded the original Kilner screens and is "not prepared to say" what the aura is; mentions colour "photographs" of the aura by Scatcherd and Baraduc in one paragraph without date, plate or reference; and carries the heading "Dicyanine cures short sight". Boddington himself warns that "suggestion and optical illusions have a definite place". - O. Bagnall, The Origin and Properties of the Human Aura (1937; pinacyanol screens): a later user of the method, with a stake in his own devices.

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Answers

1. Beer-Lambert gives T(λ) = 10^(−ε(λ)cℓ), which is at most 1 at every wavelength, so the screen can only remove light; it cannot add light from the aura or anything else. What it can change is the observer: looking at bright light through it for a minute adapts the eye's receptors unevenly (orange-yellow receptors less stimulated, red and blue relatively more), so for a while afterwards the eye's colour balance, sensitivity and focus are different. Any effect of the screen on what is seen next is an effect on the eye.

2. It rules out any asymmetry fixed to the room or the observer: uneven lighting, a lopsided afterimage, one eye stronger than the other. All of those would stay on the same side of the observer's view. It does not rule out anything fixed to the patient's body: posture and arm position, body shape and curvature, skin colour and sweat, and light reflected from the body onto the nearby background. It also does not rule out expectation, because the observer knew which side had been darker and that a swap was expected. So it shows "something about the patient", not "the aura".

3. ΔR = M²Δz/f_e² = 6.7² × 25.4×10⁻⁶ m / (0.050 m)² = 44.9 × 25.4×10⁻⁶ / 2.5×10⁻³ ≈ 0.46 D per mi. Calibrating instead from Observer A: 2 D over 4 mi = 0.5 D per mi, close to the first figure. His 2.5 mi shift is then about 1.25 D, i.e. "about 1 D". That is small for an eye: night myopia is typically 0.5-1.5 D and a 40-year-old can still accommodate about 4 D. So the shift is the right size for an ordinary change in the eye's focus, and it says nothing by itself about ultraviolet sight.

4. Kilner's own rules (PDF p.158-159) say a yellow ray shows darker on the blue band, and a red ray shows darker on both the blue and yellow bands. So on the blue band both a red and a yellow spot appear dark. Only the blue band was used in Experiments 5 and 6, so finding a dark spot says nothing about its colour; the trials can at most test whether the spot's location was found.

5. One version (the arbiter's): several observers, each prepared either with the dicyanin screen or with a sham filter of similar colour (they do not know which; Kilner's own methylene-blue screen is a ready-made sham). Behind a curtain, in random order, is a person, a warm towel or mannequin at body temperature, or nothing. The observer says "something there or not" and "which". At least 50 trials per observer, pass criteria fixed in advance, hits and misses all reported. A body-specific aura predicts person-versus-towel discrimination above chance with the dicyanin screen and not with the sham.