iiinova — where your digital self keeps evolving

John Naylor @johncnaylor.bsky.social · 13/10/2026

This eye-catching & intriguing image clearly demonstrates that at sunrise/sunset, sunlight illuminating high level clouds is less reddened than sunlight that illuminates the lower level ones. Hence the marked difference in colour. The accompanying diagram may help you to understand this.

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John Naylor @johncnaylor.bsky.social · 04/10/2026

I failed to mention an interesting feature of Entwistle's superb rainbow image: the gap between the supernumerary arcs diminishes the closer they are to the ground, implying that drop size is increasing in that direction. Young included a coloured illustrated his 1845 account of these arcs.

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John Naylor @johncnaylor.bsky.social · 04/10/2026

Thomas Young, who was the first person to explain & demonstrate the properties of light in terms of wave motion also was first to explain that supernumerary arcs are a consequence of waves interference.

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John Naylor @johncnaylor.bsky.social · 23/09/2026

Sound is a wave so diffracts wherever it encounters an object or an opening. With few exceptions, almost every sound we hear consist of a collection of wavelengths. Short wavelengths are diffracted much less than longer ones, so low frequency sounds remain audible when source is blocked.

$Waves diffract around an object. (A) Longer wavelengths wrap around an object. (B) shorter wavelengths create a shadow beyond an object$

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John Naylor @johncnaylor.bsky.social · 23/09/2026

Effects of diffraction first noted by F.M.Grimaldi c.1665. Thoroughly investigated by Newton c 1675 with his usual phenomenal attention to detail and measurement. He accepted that water waves diffract but refused to accept that the phenomenon is due to wave nature of light.

$Newton’s illustration of diffraction of waves in water traveling from A to PQ, after passing through a narrow opening, (Principia Mathematica: Motion propagated through fluids, Prop 41)$

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John Naylor @johncnaylor.bsky.social · 31/08/2026

Marin Mersenne, Minim friar, died 1 Sept 1648. He was the first person to discover experimentally how the frequency of a vibrating wire is related to its physical characteristics, to measure the speed of sound (by echoes & gunfire), and to determine the least pitch audible to humans is 16Hz.

Marin Mesenne
8 Sept, 1588 - 1 Sept, 1648

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John Naylor @johncnaylor.bsky.social · 31/08/2026

Hermann v Helmholtz, born 31 Aug, 1821, not only the foremost authority on the optics of the human eye during latter half of 19th C., he was also the leading authority on the perception of sound and its relationship to music. Author of “On The Sensations Of Tone” & “Treatise on physiological optics”

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John Naylor @johncnaylor.bsky.social · 14/08/2026

Colanders are so passé. The shape of the hole is immaterial as long as the distance to the screen is a least 110 times hole diameter. First explained by J.Keppler in 1600. He named these pinhole images "figurationes lucis ".

When a screen with holes of different shapes is close to a screen, the images match those of the holes.

At a suitable distance the images match the source, here the crescent sun during eclipse. They are not perfectly in focus because the holes in this case are approximately 0.75cm.

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John Naylor @johncnaylor.bsky.social · 14/08/2026

Gringos on eclipse safari in the Wimbledon Common savannah

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John Naylor @johncnaylor.bsky.social · 10/08/2026

For all the recommendations to view the upcoming eclipse using colander, the use of a sieve or crossed fingers to project eclipse image is nothing new. See "Problemata" Book 15, sec 11, a work attributed to Aristotle c. 350BC, but likely by his followers.

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John Naylor @johncnaylor.bsky.social · 09/08/2026

Bees are sensitive to near u.v. and insensitive to the red end of the spectrum, so in theory can see uv rainbows (but not rosy sunsets?). Diagram from p. 274 of my vade mecum of optics "Seeing the Light, Optics in Nature, Photography, Colour, Vision and Holography" by D.Falk, D.Bril. D.Stork.

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John Naylor @johncnaylor.bsky.social · 09/08/2026

Multispectral rainbow photos by Andrew Steele. These three images are of the same bow using i.r. and u.v. filters. The central portion is of the visible light bow, below this is the infrared bow and above it is the ultraviolet bow. Newton, of course was unaware of these invisible radiations.

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John Naylor @johncnaylor.bsky.social · 09/08/2026

SOLAR ECLIPSE: Earth and Moon both orbit the Sun in the same direction, but at this point of their orbits Earth is travelling faster than the Moon. Hence the Moon’s shadow moves across Earth’s surface from west to east as the Earth overtakes the Moon.

To understand the mechanics of a solar eclipse bear in mind (1) both Earth & Moon orbit the Sun in the same distraction & (2) at this point in their orbits, Earth moves faster than the Moon

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John Naylor @johncnaylor.bsky.social · 20/07/2026

Shadows are an important clue to the position of an object with relation to the ground. Cover up the “shadow” in each of these photos.

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John Naylor @johncnaylor.bsky.social · 20/07/2026

It seems that our visual system is primed from the very start to assume that the world is lit from above. Hence this compelling illusion.

Shading creates the illusion of convexity & concavity even though the surface is perfectly flat

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John Naylor @johncnaylor.bsky.social · 16/05/2026

Why do the most distant reflections of the perfectly circular holes appear to be hexagonal?

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John Naylor @johncnaylor.bsky.social · 16/05/2026

Daliesque reflections in water

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John Naylor @johncnaylor.bsky.social · 10/05/2026

The wave theory of light was originally proposed by T. Young. Fresnel developed the necessary mathematical underpinnings of the theory. Despite their cordial relations,Young always considered the wave theory as his brainchild and maintained that Fresnel had merely extended his ideas.

Despite their cordial relations, Young always considered the wave theory as his brainchild and maintained that Fresnel had merely extended his ideas. Late in 1824, an exasperated Fresnel felt it necessary to put him right.

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John Naylor @johncnaylor.bsky.social · 30/04/2026

And there’s a challenge. Can you identify something just from the sound it makes when it is lashed by rain or blasted by wind? It’s not impossible, though it takes not a little practice. Thomas Hardy learned to do so, as is obvious from the opening paragraph of his "Under the Greenwood Tree"

Under the Greenwood Tree by Thomas Hardy

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John Naylor @johncnaylor.bsky.social · 02/04/2026

Born OTD, F.M.Grimaldi, c. 1640 carried out a wide ranging experimental investigation into the properties of light as they were then known, with a view to investigating the Peripatetic idea that light is an accident, i.e. a quality, rather than a substance & in the process discovered diffraction.

Francesco Maria Grimaldi, Jesuit mathematician, 2 April 1618 – 28 December 1663

$(a) Sunlight enters a darkened room through a narrow opening AB. FE is a small disc casting an umbra GH and penumbra IL. Grimaldi noticed that the penumbra is surrounded by faint, coloured bands extending to M & I. (b) Grimaldi’s diffraction. Sunlight enters a darkened room through a narrow hole CD. EF is a board, GF a hole larger than CD. The geometric edge of the spot of light should be NO. But the spot itself extends beyond this to I and K$

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John Naylor @johncnaylor.bsky.social · 31/03/2026

I am enthralled by the aesthetic qualities of the sounds I encounter daily. But, for me, the real reward of listening is to make sense (i.e. understand the physics) of the process responsible for this or that sound. To that end I find oxfordwaveresearch.com/products/spe... invaluable.

Reflection tones (captured here by SpectrumView) are due to interference between sound from the source & its reflection by the ground.

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John Naylor @johncnaylor.bsky.social · 31/03/2026

born OTD 1596, René Descartes, the natural philosopher who gave the first correct mathematical account of the angular dimensions of the primary & secondary arcs of the rainbow.

René Descartes, natural philosopher, 31 March, 1596 - 11 Feb, 1650

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John Naylor @johncnaylor.bsky.social · 26/02/2026

Many people can detect polarised light because they see a faint butterfly shaped yellow spot when looking at a broad expanse of polarised light such as the zenith sky at midday or a blank computer screen. "Haidinger's Brush" particularly noticeable if you rock your head from side to side.

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John Naylor @johncnaylor.bsky.social · 26/02/2026

Malus’ discovery was seized upon by François Arago. in 1811, holding a sheet of mica up to the sky and examining it through Iceland spar to investigate the resulting polarisation colours, he inadvertently discovered that skylight is strongly polarised in a direction perpendicular to the sun’s rays.

The first quarter moon always falls within the band of maximum polarised skylight because both are 90° from the sun. This image was taken at sunset looking due south

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John Naylor @johncnaylor.bsky.social · 24/02/2026

Any given portion of the #rainbow arc can be almost entirely extinguished by viewing it through a polarising filter and rotating it.

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John Naylor @johncnaylor.bsky.social · 24/02/2026

Rainbows are almost 100% polarised because its spectral colours within a drop are reflected close to the Brewster angle between water and air—i.e. within water—which is approximately 37°. First observed in 1811 by J-P Biot.

Rainbow ray corresponds to light undergoing minimum deviation (42° for red light)

Rainbows are tangentially polarised, i.e. max polarisation parallel to arc

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John Naylor @johncnaylor.bsky.social · 23/02/2026

I should point out that, coincidentally, Malus, the man who discovered in 1808 that polarisation is an intrinsic and fundamental property of light, thus overturning Huygens’ claim that polarisation occurs because light is modified by refraction, died on this day in 1812

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John Naylor @johncnaylor.bsky.social · 23/02/2026

A short video to illustrate the effect of looking through a crystal of Iceland spar as it rotates.

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John Naylor @johncnaylor.bsky.social · 23/02/2026

d. #OTD, 1812, É-L Malus, in 1808 noticed that the reflection of setting sun in a widow though Iceland spar fade as he rotated the crystal & surmised that polarisation is an inherent property of light, overturning Huygens’ idea that occurs because light is modified by refraction.

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John Naylor @johncnaylor.bsky.social · 21/02/2026

Numerous examples of sound being heard at great distances from the source. The most remarkable example is that the 1883 eruption of Krakatoa which was heard on Rodriguez, 4800 km away: "the sounds were very distinctly heard, and were supposed to be those of guns fired by a vessel in distress"

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John Naylor @johncnaylor.bsky.social · 21/02/2026

A chance observation helped Reynolds to visualise the effect of wind shear on the propagation of sound on a windy day. While walking along a stream he noticed that ripples produced by water dripping from a pipe into the water close to the bank do not spread uniformly, as in this video

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John Naylor @johncnaylor.bsky.social · 21/02/2026

d. #OTD, 1842 O. Reynolds, engineering prof, established experimentally that wind shear & atmos temperature variations cause sound to refract so that under some circumstances sounds can be heard at much greater distances than normal & at others not heard at all, though the source may be visible

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John Naylor @johncnaylor.bsky.social · 17/02/2026

b #OTD 1740 Horace Bénédict de Saussure, Swiss natural philosopher famous for his ascents of Alpine peaks. He invented the cyanometer (1789), a graded scale of blues used to assess intensity of sky colour, and thus (he believed) state of weather. Used by v. Humbolt in his S.American journeys.

De Saussure's cyanometer has 52 shades of colour. V.Humbolt estimated the sky seen from the summit of Chimborazo to be 46 on the cyanometer scale.

Cyanometer is a useful tool if you want to acquaint yourself with the variability of sky collours, though it is not a weather prognosticator.

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John Naylor @johncnaylor.bsky.social · 17/02/2026

b #OTD 1781, René Laennec, pioneer of auscultation, diagnosis by listening to bodily sounds through a tube. Doctors in his day liked that his tube made it unnecessary to place the ear in contact with the body of an unwashed and possibly unhygienic patient and did not invade a woman’s privacy!

Laennec's account of how he came up with the device

Laennec's tube, a forerunner to the stethoscope

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John Naylor @johncnaylor.bsky.social · 16/02/2026

b OTD 1822 polymath Francis Galton. Interested in the limits of human hearing, he invented a whistle capable of producing ultrasounds up to 55kHz. He used it to test the hearing of people, usually without letting on that he was doing so, and tested every creature in London Zoo.

Francis Galton, 16 Feb 1822 - 17 Jan, 1911

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John Naylor @johncnaylor.bsky.social · 09/02/2026

d OTD 1650, René Descartes, the natural philosopher who in 1637 published the first correct mathematical account of the angular dimensions of the primary & secondary arcs of the rainbow.

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John Naylor @johncnaylor.bsky.social · 28/01/2026

Died OTD, French physicist, Felix Billet, published in 1868 results of an experiment in which he illuminated a thin, vertical stream of water with sunlight and managed to see 19 rainbow orders including supernumeraries. He named it “la rose des arc-en-ciel”, known in English as Billet’s Rose.

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John Naylor @johncnaylor.bsky.social · 26/01/2026

You may be interested in Wollaston's diagram of how he observed the absorption lines. Not by projection, but by looking at the slit through a prism. His paper on the subject was published in Phil Trans 92, p365: "A Method of examining refractive and dispersive by prismatic Reflection"

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John Naylor @johncnaylor.bsky.social · 15/01/2026

Puddles enliven a walk, as Ruskin knew well!

John Ruskin, Modern Painters Vol 1, Section V. Ch1. p. 496 ‘The truth of water’

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John Naylor @johncnaylor.bsky.social · 14/01/2026

I went the the Natural History Museum (London) In June 2019 to see Luke Jerram's splendid Museum of the Moon. Although the surface of the sphere was smooth, the shading fooled one's eye into interpreting it as embossed. My tactile acuity with Braille map didn't my match visual acuity!

Braille Moon Map provided for visitors to Museum of the Moon exhibition

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John Naylor @johncnaylor.bsky.social · 02/01/2026

Moire patterns are often noticed as one's view of the elements that create them changes. Here is a short film of a moire formed by Venetian blinds and a garden fence with open horizontal slats.

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John Naylor @johncnaylor.bsky.social · 01/01/2026

Same here. I wonder if noticing these patterns depends on knowing what to look for, because they are often rather subtle. I am inspired to send you a sieve/shadow moire. Sieve resting on sheet of paper & illuminated from above. May 2026 be a year in which we come across unusual ones

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John Naylor @johncnaylor.bsky.social · 31/12/2025

This morning frost on a plastic manhole cover reveals the embedded metal grid that strengthens it.

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John Naylor @johncnaylor.bsky.social · 13/12/2025

The first systematic measurements of the speed of sound in water were made in Lake Geneva in November 1826, by Daniel Colladon a Swiss physicist, with the help of his father, some two centuries after the earliest measurements of the speed of sound in air.

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John Naylor @johncnaylor.bsky.social · 04/12/2025

L. Galvani d OTD, became interested in animal electricity when a student dissected a frog’s leg while another operated a static electricity generator, noticed that when it sparked the frog’s leg contracted involuntarily. Is it possible to claim a frog, martyr to science, had picked up a radio wave?

Galvani'd laboratory. The spark generator is on the left hand side of the bench.

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John Naylor @johncnaylor.bsky.social · 30/11/2025

E.Chladni b OTD 1756, known for the patterns formed on a glass plate sprinkled with fine sand & exited with a bow, was also the first person to measure the speed of sound in gases other than air by comparing the pitch of an organ pipe filled with a gas with that filled with air.

Chladni demonstrating the patterns that can be created when a glass plate is exited by bowing its edge

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John Naylor @johncnaylor.bsky.social · 28/11/2025

Among his many interests, Athanasius Kircher d OTD 1680, Jesuit scholar was fascinated by architectural acoustics & unusual echoes. He found many examples of buildings that combine these things, among which was Villa Simonetta which had a remarkable flutter echo. Bombed during WW2

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John Naylor @johncnaylor.bsky.social · 22/11/2025

Reflections from window panes illuminated by low sun. If air pressure within the space between glass double glazing is below atmospheric pressure the panes become concave and reflect light as shown in diagram. Red rays create bright cross due to surface distortion because glass held in square frame

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John Naylor @johncnaylor.bsky.social · 19/11/2025

We can only see a single colour emerging from any given drop which is why a #rainbow requires a multitude of drops. This is evident in sunlit drops that twinkle as one moves one's gaze across a dew laden lawn.

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John Naylor @johncnaylor.bsky.social · 19/11/2025

Whether you see a full arc or only a segment of a #rainbow depends on the height of the sun, horizontal extent of the rain shower and, as here, how close you are to it. And, of course, as you approach the shower, the position of the arc relative to the background changes.

The closer you are to the shower, the more complete the arc.

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