John Naylor

As we say in Britain: “a slap-up dinner”

Author of 1737 "Il Newtonianismo per le dame", an account of Newtonian optics.Translated by Elizabeth Carter in 1739: "Sir Isaac Newton 's Philosophy Explain'd for the Use of the Ladies,

Despite Whewell's coining the term "scientist" in 1833, the term
did not come into general use in the English-speaking world until the 1860’s. Faraday always insisted that he be known as a "natural philosopher".

I know the feeling!

Some 40 yrs ago a knife grinder with a treadmill would occasionally visit our street in our corner of the woods (SW London). Haven't seen him since. Then, surprisingly, a couple of weeks ago a woman knocked on our door asking if we needed our knives sharpened. I sharpen mine, so declined.

Mine too! Moonlight always enchants me.

'Blood rain' and fiery sunsets as Saharan dust sweeps UK North African dust carried to the UK by a weather system are forecast to have some unusual effects in the coming days.

I think BBC weather is wrong about this. Saharan dust is not in itself responsible for rosy sunset skies. Dust particles are too large to cause Rayleigh scattering, which is the source of sunset colours. Clouds of dust reflect sunset colours, as do clouds of water.
www.bbc.co.uk/weather/arti...

Newton wanted to use F's data for the 2nd ed of Principia & managed to have a bowdlerised version of the catalogue published in 1712. F prevailed & was allowed to collect and destroy the all the available unsold copies of the unauthorised catalogue. Newton removed all references to F from Principia!

These days he’ll have tattooed arms & a man bun

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.

Just realised that I have uploaded the unfinished image. It's known as Haidinger's Brush

Not sure what you want to know

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

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.

Opposition effect around top of shadow

First & last quarter moons are 90degrees from sun so always fall within band of max polarised skylight which is also 90 degrees from sun. Confirm with polarizing filter, should visual confirmation be required

Ditto cloudless skies!

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

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

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

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.

Also a waste of a finite resource: helium

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

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

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.

Would curling be viable as a competive game if the collisions were inelastic?

Within living memory, Shetland Islanders regarded a rainbow over a house as presaging the imminent death of one of its occupants, clearly a reference to the rainbow’s role as a soul bridge.

Elastic collisions

Great image. Just copied image & turned it 180°, which makes the trees & sky appear to be in a mud frame.

You should point out that the bow visible in the image is NOT visible to the child, who sees a different one. (Bow always centered on the observer's eye)

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"

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

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