Shine a light on rainbows
QUESTION Why is the most visually distinct part of a rainbow the part closest to the ground?
RaindRops coalesce and increase in size as they fall, but they can also collide and split. all sizes of raindrop contribute to the rainbow near its base, and the larger array of drops makes this part of the bow bright and colourful.
only smaller drops contribute to the top of the arch and these produce a less intense, more pastel rainbow.
Rainbow physics is fiendishly complex. The traditional descartian theory assumes perfectly spherical raindrops. However, they are not the tear-shaped objects beloved of illustrators.
The smallest raindrops are kept strongly spherical by surface tension forces. Larger drops are flattened by air resistance as they fall, developing a shape like a burger bun.
The reflection and refraction of light from a flattened water droplet is not symmetrical. This is why we see rays only as we view them horizontally, that is, near the base of the rainbow. Thus, the rainbow produced by large drops is bright.
Furthermore, the purity of rainbow shades are determined by the extent to which the component monochromatic colours overlap. This, too, is determined by the droplet size.
Uniformly large drops with a radius of above 1mm create bright rainbows with pure colours. smaller drops are blurred. For very small droplets with a radius of 0.01mm, the overlap of colours is so great that the resulting light appears to be almost white.
J. K. Wileman, Worcester.
QUESTION How are farmed shrimps and prawns de-shelled?
AN ABUNDANT supply of cheap labour in developing countries means prawns are mainly de-shelled by hand.
around 75 per cent of prawns come from asia. The two leading producers are China and Thailand, followed by Vietnam, indonesia and india. Much of the remainder comes from Latin america.
Lines of workers de-head the prawns, which are then washed, graded into size (this part is usually mechanised) and then the shell is gently pulled away.
Larger prawns must also be de-veined, which is a tricky operation performed with stainless steel razor blades or scissors. depending on prawn size, accomplished hand peelers can average six to 12 shell/vein removals per minute.
Workers wear hair nets, gloves, mouth masks, protective smocks and rubber boots. They must walk through a foot bath of disinfectant on their way to stainless steel tables and conveyors at enclosed, temperature-controlled work stations in modern buildings.
as the size of the global prawn market
has increased, sophisticated mechanisation has speeded up the process.
The companies Laitram Machinery and Gregor Jonsson in the U.s., Martak in iceland and KM Fish Machinery in denmark make de-shelling machines.
a clamp grabs a prawn, the shell is cut and the vein removed before pins pull away the shell. The de-shelled prawns can then be washed and graded.
Modern grading machines use laser imaging and computer vision algorithms. There are also machines for steam cooking or chilling live shrimp.
A. L. Downey-Roberts, London N9.
QUESTION Why do actors and singers call themselves artists?
THIS goes back to the ancient Greeks and the cult of sister goddesses known as the Muses.
Every four years, a festival was held in their honour at Thespiae in Greece, from which we get the word thespian, meaning an actor.
This festival included singing, dancing and poetry, which became the basis on which plays were performed.
Homer’s odyssey formalised the Muses into a group of nine, each responsible for the patronage of different forms of art.
They were Clio (history); Euterpe (tragedy and flute playing); Thalia (comedy); Melpomene (tragedy and lyre playing); Terpsichore (dance and lyric poetry); Erato (lyric and erotic poetry); polymnia (poetry and geometry); Urania (astronomy); and Calliope (epic poetry), who was their chief.
Tragedy in this sense means poetry or drama that wasn’t intended to be amusing or satirical.
These talents were considered by the ancient Greeks to be arts, while painting and sculpting were crafts, so the poets and performers were the first artists.
Though the Muses were always considered to be unmarried, they are often referred to as the mothers of famous sons, such as orpheus, Theseus and Eumolpus, who were known for their musical or poetic skills.
From the word Muse we get museum, a place where works of art are kept. The first museum was in alexandria around the time of pharaoh ptolemy soter, 367 BC to 283 BC.
Robert Sutherland, Northampton.
QUESTION What is the story of RAF fighter pilot the Night Reaper?
FURTHER to RAF pilot Karel Kuttelwascher and his Hurricane Mkii night Reaper, my father-in-law sid Moston DFM was a World War ii spitfire pilot with a literary bent.
He thought the name the scarlet pimpernel (‘they seek him here, they seek him there’) was fitting and asked the ground crew to paint his aircraft’s nose cone scarlet and add the words The scarlet pimpernel.
Either mishearing his request or as a joke, the nose cone was duly painted scarlet, but to his chagrin, it was emblazoned The scarlet pimple.
i think he eventually ‘pranged that kite’, but survived the war unharmed.
Neil Matthews, Swanmore, Hants.
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