Different light: Newton and the spectrum

This is the next sample from They Saw the Difference.

When I was three, my bedroom had the leadlight windows that were popular as a bit of middle-class poshness in the 1930s, when our house was built. These windows were made of small pieces of glass, held together between H-shaped strips of lead. Each window had one special piece of extra clear glass with bevelled edges, and these gave me one of the wonders of my youth.

The windows faced west, and at certain times of the year, when the low afternoon sun shone between the houses across the road, it hit these angled pieces of glass, and a small coloured patch appeared on my wall—my own private rainbow, captive in my room. 

Any triangular piece of glass will bend light, and the light is split because each of the colours is refracted by a different amount, because each colour has a different wavelength. If we want to see the effect well, it is best to use a narrow beam of white light, and pass it through a prism in a darkened room. Newton saw it, and wondered why the light was different.

A prism is just a solid figure that is essentially triangular in shape and made of a transparent material. Prisms are commonly used in physics to deviate or disperse a ray in optical instruments or laboratory experiments, or to deliver total internal reflection. Here is how Newton set up his investigation:

 

In this diagram, white light comes
from the right and is dispersed.

One thing is certain, this three-year-old was too late to make any original discoveries, because Newton completed his systematic study of the spectrum, long before I was born. In 1666 he saw the composite nature of white light while carrying trying to minimise chromatic dispersion in lenses, an annoying effect that had been known for about fifty years, when telescopes and microscopes gave images with coloured fringes. 

In 1672, Newton told the world how he had studied the ‘celebrated phenomenon of colours’. At the time, most people assumed that colour was a mix of light and dark, that the prism somehow added the colour. and Robert Hooke was one of the strongest supporters of this view.

With two neat experiments, Newton demolished Hooke’s ideas, and began one of the great feuds of science. (In case you don’t know it yet, science is driven by spotting differences, but there’s always room for personal differences, and many of the wildest brawls revolved around Newton. By comparison, Dart’s clashes with the Piltdown gang {see the last blog} were nothing!) 

In one experiment, Newton used a second prism to pull the colours back together again, and showed that the result was white light. Then he used a second prism and a slit to show that when a selected band of coloured light passed into the second prism, it passed on unchanged. Hooke’s theory was in tatters, and Newton had an enemy for life. Newton wrote no more on optics until after Hooke died in 1703. 

 In fairness to a rather peculiar man, Newton simply could not help bursting out with the truth, even if it got up people’s noses! Novelist Aldous Huxley assessed Newton this way: 

If we evolved a race of Isaac Newtons, that would not be progress. For the price Newton had to pay for being a supreme intellect was that he was incapable of friendship, love, fatherhood, and many other desirable things. As a man he was a failure; as a monster he was superb.

How Newton’s experiment
is often wrongly shown.

Newton’s experiment is often shown like this, upside down, with a triangular prism sitting on its base, the light coming from below, bending down as it passes through the apex and being directed further down on the other side. Newton used sunlight shining down (not up!) through gap in a window, and being bent through the apex of an upside-down prism to shine upwards onto a wall, 22 feet (7 metres) away. 

We know the sitting-on-its-base-prism picture is wrong, because of the angle of the incoming beam, and besides, the band at the top is ultraviolet (above violet), while that at the bottom is infrared, meaning below red. The prism had to be point-down. The room must have been darkened, with just one beam of light entering the room and throwing a pale spectrum onto the wall, red at the bottom, violet at the top. 

Newton called the colours ‘spectrum’, a Latin word meaning spectre or apparition, and he is said to have been the first to see a prism, but I wonder how many others had found their own private rainbows before him, given that he spoke of the ‘celebrated phenomenon of colours’. 

Those celebrated colours were just those of the rainbow, but how many were there? Almost everybody had their own version. In fact the spectrum contains an infinite number of colours, and the number we ‘see’ is subjective. Newton followed a Greek astronomer named Ptolemy who had said there were seven colours, and gave them the names we use today: red, orange, yellow, green, blue, indigo and violet. 

 He said he could not separate any further colours from any narrow band of light selected from the spectrum, but his set-up would never have given monochromatic light in any selected band, because the rays from the Sun are not completely parallel. He should have seen further separation, but perhaps he intended his ‘result’ to be taken only as an idealised case. Or maybe he fudged his experiment: he stated correctly that different colours are refracted (bent) through different angles, both in prisms and in lenses, and that was the important part. 

What we now call visible light is just a small part of a much larger electromagnetic spectrum, but as we will see in chapter 5, this took time to find, and it is important to note that this is just the range that we humans see. There are many insects, bees for example, which are different because they can see ultraviolet light. 

So how do you see something that cannot be seen? In 1799, an astronomer named Sir William Herschel was measuring the temperatures associated with different colours. He had been using filters to view the Sun, but he saw how some filters that he used when examining sunspots let more heat through.

This led him to wonder if different colours had different amounts of heat, and he used thermometers to measure the strength of heating along a normal spectrum. He did this because his observations made him speculate that: 

 …the prismatic rays might have the power of heating bodies very unequally distributed among them…If certain colours should be more apt to occasion heat, others might, on the contrary, be more fit for vision by possessing superior illuminating power. 

Herschel found a higher temperature near the red end, and testing just beyond the visible range, found an even higher temperature, so he named this radiation ‘calorific rays’. He showed that these invisible rays behaved like visible light, being reflected, refracted and transmitted, the same tests Heinrich Hertz later applied to his radio waves. 

Herschel delivered a number of papers on the subject to the Royal Society in 1800, describing several hundred experiments on what he called “invisible light”, and since then, infrared astronomy has increased in importance as more sensitive instruments to detect infrared radiation have been developed. We will look more at infrared and infrared astronomy in the book. 

Johann Ritter tested the ultraviolet end of the spectrum, using silver chloride to detect radiation beyond violet. Photographers would later use the way light makes silver chloride go black, but Ritter found that there was an invisible band of radiation, even better than white light at blackening the silver chloride, which we now call UV. 

To sum up, the visible part of the electromagnetic spectrum, ranging in wavelength from approximately 3.9×10-7m (violet) to 7.8×10-7m (red) (corresponding frequencies 7.7×1014 Hz and 3.8×1014 Hz, respectively). 

As Aldous Huxley reminded us, Newton was unpleasant. He mistreated Stephen Gray, he quarrelled with Robert Hooke over the inverse square law and his theory of colour, with Gottfried Leibniz over the invention of calculus, and with Christiaan Huygens over his theory of light. 

Even so, any one of Newton’s achievements would have been enough to ensure his fame, even without the apple. But did the apple really fall? We will never know now, but the tale was made popular by Voltaire, and Newton’s biographer and friend, William Stukeley, claimed Newton told him the story, so maybe there was a day when the apple fell, and made Newton wonder why it should be so. That is Newton’s greatest gift to us, that he asked why as often as he did, even inspiring poets like Paul Valéry and Alexander Pope, who wrote: 

Nature and Nature’s laws lay hid in night:

God said ‘Let Newton be.’ and all was light. 

Mind you, Sir John Collings Squire would later add:

It did not last: the Devil shouting ‘Ho, 

Let Einstein be.’ restored the status quo. 

Newton told Hooke that if he had seen further than others, it was because he had stood on the shoulders of giants. This may have been a snide dig at Hooke, but a similar remark had been made by many others, centuries earlier. Robert Merton has even written a whole delightful book (On the Shoulders of Giants), on the subject, tracing the earlier history of the aphorism.

It was once cited with this brilliant typo: 

Merton, Robert K., On the Shoulders of Grants: A Shandean Postscript, Harcourt Brace, New York, 1965. 

—Max Charlesworth, Lyndsay Farrall, Terry Stokes, David Turnbull, Life Among the Scientists, Oxford University Press, 1989, bibliography, 295.

Next, we'll look at the spectroscope and what it can do.

A Different Brain

 This is the first part of They Saw The Difference, announced here.

Dart’s original illustration of
the Taung child, 1925.

I have always told my students that the best actors go into law, the next best become teachers, and the leftovers go to stage and screen. The reader may justly conclude from this that when I teach (or write) I’m putting on a show.

About 1992, I prepared for work each day by slipping the fossilised toe-bone of a giant kangaroo into my shirt pocket, a child’s brain into one trouser pocket and its skull into the other.

<SFX> Brakes screech, voices off, shouting “Wha-a-at?”

To clarify, the skull and brain were fossils, 2 to 3 million years old, plus or minus a bit, and if the kangaroo toe-bone was real, museums around the world make casts of their best and rarest examples to sell to other museums, so what you see in a glass case or a lecturer’s hand is usually a copy, cast in resin from a mould of the original, and painted to resemble the original, which is somewhere safe. No matter, just having casts of the skull and part of its brain in my pockets allowed me to tell their story, as well as if I held the genuine relics.

Raymond Dart was an Australian teaching in South Africa in the 1920s. In 1924, he received two boxes of rocks on a morning when he was supposed to be getting ready to act as best man to his friend, Christo Beyers. Peeking into one of the boxes, he saw the cast of a brain lying loose, and in that, he saw something important.

Soon after the brain’s owner died, mud partly filled a skull, and this mud later hardened to rock. Technically, it was an endocast, a copy of part of the inside of the skull which closely reflected the brain, but it wasn’t any old brain—it was special, because of its small size and the position of its brain stem.

Interpreting fossils is an art and a science. Experts must know anatomy, how the parts work together, what small differences mean, and they work with those small differences. The position of the large hole in the skull where the spinal cord leaves the brain, the foramen magnum, was immediately obvious in the shape of the brain. Any animal with a brain stem like that had to have walked upright.

We cannot be certain how the Taung child died, but clearly the skull had ended up on its side in a lime-rich deposit, where the brain case was slightly more than half-filled with the mud which became the cast.

Dart saw that it fitted into a block of stone in the case, so a major part of the brain owner’s skull was probably there as well. He was a medical man, but fascinated by fossils, and he knew that this was important.  So was his friend's wedding, but afterwards, he itched to get back to his find.

The covering rock had to be carefully removed before the face could be examined, but a quick look at the cast was all Dart needed. The brain said this animal had a skull which attached to a vertical spine, lying directly below the skull, rather than behind it, as in chimpanzees and gorillas. The owner walked upright, like modern humans. Here is how Dart worked it out:

I was also convinced from the earliest period of my investigations that these creatures had placed great reliance on their feet for walking and running and that, consequently, their hands must have been freed for other tasks. This was implicit in the globular form of the skull which was obviously balanced on a more vertically placed type of backbone than that of a gorilla or chimpanzee. The improvement in the poise of the head implied a better posture of the whole body framework, since there must have been a relative forward displacement of the foramen magnum (the hole in the base of the skull which links the brain with the spinal cord).
—Raymond Dart, Adventures with the Missing Link, 1959, 11.

The people who interpret fossils work like Sherlock Holmes at his best. To those who can read, a glimpse of a document can be enough, but those who can read fossils can gain just as much from a single glimpse of just the right hint. At this point, Dart made a political mistake.

Even in the 1920s, a careful observer would have seen that the British Empire was already in decay, and there were few careful observers around, but there was a cast-iron rule: London is always right. When Dart reported his find in Nature in 1925, London came down on him like a ton of bricks.

His find (known as the “Taung child”, from where it was found and its obvious youthfulness) was small-brained and most British scientists were certain that any small-brained thing was no ancestor of theirs. Piltdown Man was the human beginning, they said: he had a big brain, and best of all, he was found in Britain! (There’s more on Piltdown in the Afterword, but you'll have to get the book to read that.)

Today, we might think Dart’s name for his find, Australopithecus (“southern ape”), was not the best name for an upright-walking individual, even one with a small brain, but Dart was trying not to draw too much fire upon himself. It didn’t work, but in the long run, the brain stem evidence held up and Piltdown was eventually shown to be a fake.

The true status of the Taung child lay hidden inside its jaw until 1987. In both humans and the other apes, the “adult” teeth emerge in a specific sequence. There is one order of appearance in humans, and a different order of tooth eruption in the other apes. Concealed inside the Taung child’s skull, teeth were erupting, and their pattern of development would tell us what the Taung child was, either human or ape. As there is only one Taung child, you cannot slice it up, just to see what is inside. You could take X-rays, but there is too much other material in the way, and the things we are looking for are much too faint.

For many years, it seemed as though we would never know what was inside the jaw. Then in 1987, Glenn Conroy and Michael Vannier had a bright idea. Instead of cutting the skull into thin slices, they made a series of virtual slices with X-rays, and fed the results into a computer, and used back projection to build up a three-dimensional picture of what was inside. Seeing how the Taung baby’s teeth were erupting would give the answer.

The researchers took their X-ray shots, just 2 mm apart, in three different dimensions: vertically, from front to back, vertically, from side to side, and horizontally. (They called it the sagittal, coronal and transaxial planes, if you prefer the technicalities.) The method is less important, but the answer was delightful:

…the Taung ‘child’ is not a little human, but just as important, it is not a little ape…
— Glenn C. Conroy & Michael W. Vannier, Nature 329, 625–627, 21 October 1987.

The whole answer was told in the differences: the Taung baby is a betwixt-and-between, a half-and-half, a missing link if you wish, and we would never have known if the two researchers had not decided to give it a CAT scan! Sadly, we had to wait another sixty years to find out what it was.

The story I told, over several years at the Australian Museum, was about how Dart saw a difference, and recognised a new scientific truth. This was just a few years after Conroy and Vannier had confirmed the role the Taung child’s people played in our origins, but there was more: I had human and gorilla skulls, that toe bone of the giant kangaroo and the matching bone from a horse. Always, it was about differences.

At other times, I talked to my audience about Edward Tyson (1651 – 1708), one of the unsung heroes of science, who persuaded Robert Hooke to pay seven shillings and sixpence for a 43 kg porpoise from a London fishmonger, so Tyson could dissect it. Back then, even experts like John Ray called the porpoise a fish, but Tyson’s Anatomy of a Porpess, published in 1680 showed the danger of judging a book by its cover. He said: “If we view a Porpess on the outside, there is nothing more than a Fish, but if we look within, there is nothing less.”

Tyson later dissected an infant chimpanzee which had died after being brought to London from Angola. While he referred to it as both a ‘pygmie’ and an ‘Orang-Outang’, the drawings show a chimpanzee, but Tyson’s book, filled with illustrations, showed for the first time just how close humans were to the other animals, and how they differed.

If Copernicus had removed the earth from the centre of the universe (something I describe in chapter 10), Tyson and his assistant, William Cowper, helped to remove Homo sapiens from a central position in creation. This change tied together humans and the whole of ‘lower’ creation. Tyson had taken one of the crucial steps towards recognising that evolution happened.

Next, back to Newton again…

They saw the difference

 I am, first and foremost, an historian of science, and I'm going to talk for the next month or so about my new e-book, soon to be a print-on-demand book, called They Saw the Difference. The thing is, I've been busy getting our block of townhouses repainted and rejigging a couple of older titles. so for now, here's the introduction to They Saw the Difference.

I keep six honest serving-men
(They taught me all I knew);
Their names are What and Why and When,
And How and Where and Who.
—Rudyard Kipling, introduction to ‘The Elephant’s Child’ in the Just So Stories.

Differences, seeking, cultivating and studying them, make our civilisation work. The art of noting and celebrating differences bloomed in Renaissance Europe, and detecting differences shaped modern science and technology, but the habit was there long ago.

The early hominin who saw that this rock was better than that rock for forming tools, or observed that wood burned and rocks did not, the one who noticed that water ran downhill and not up, these were the ancestors of modern scientists and technologists.

My granddaughters
seeing the difference
an echidna makes.

As the subtitle says, this is a social history of science, concentrating on the why and the how, with a good dollop of what, and something of the who, where and when, along with regular bursts of something completely different. This book compulsively pursues puzzles to their ends.

For example engineers and physicists, hunting for scraps of literary icing to decorate their published work often quote these words of Paul Ambroise Valéry (1871 – 1945): “One had to be a Newton to notice that the moon is falling, when everyone sees that it doesn’t fall.”

If the quoters offer a source (most of them don't), it has a date of 1970, which is well after the poet’s death. By enlisting the burrowing skills of Project Wombat, I know that their 1970 source is volume 14 of Valéry’s posthumous collected works, but the quote was first published as “Il fallait être Newton pour apercevoir que la lune tombe, quand tout le monde voit bien qu’elle ne tombe pas,” in Mélange, Grandeurs, 384, Oeuvres, t. 1, La Pléiade, in 1939. I sweat the details to get the backstory.

“Is there any point to which you would wish to draw my attention?”
“To the curious incident of the dog in the night-time.”
“The dog did nothing in the night-time.”
“That was the curious incident,” remarked Sherlock Holmes.
—Arthur Conan Doyle, ‘Silver Blaze’, in The Memoirs of Sherlock Holmes.

Valéry knew what was going down when Newton’s apple fell. He didn’t imagine crazy young Isaac, sitting under a tree, thinking “apple, falling: that’s odd!”. Newton was differently equipped, mentally speaking, but he knew his apples. To him, the odd thing wasn’t the falling apple, it was the curious way the moon failed ever to reach Earth. That was his dog that didn’t bark in the night.

He saw that the moon’s orbit involved a fall that went on forever (in our time frame), the descent always cancelled out by the satellite’s forward motion. That was the difference he saw, a whole branch of science sprang from it, and Paul Valéry could see that. We will return to Isaac Newton again soon, because he could see differences, and he also made a difference.

I chose to follow, not the broad highways of science, thronged by the famous and important, but rather to stray down the alleys and dusty tracks, where the interesting people and the curious science lie in wait for us. I have enjoyed making this work, written for the child I once was and still am: I hope you find some of the same joy.

Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.
— Robert Frost, The Road Not Taken.

Back in the saddle

 Well, the past three months have been a bit of a rush. I finished editing and compiling Old Grandpa's Book of Practical Poems, mainly for my grandchildren, and that was going to be it, but there was an old ms, lingering on my hard disc, a novel with the working title Sheep May Safely Craze. That is now (as of this morning) locked up and being submitted.

No sooner had I got into the sheep than I attended a kid's lit function, and before I go on, I need to comment. An over-rated novelist once said in a radio interview that he might write for children, “but only if I had brain damage”. This got right up the noses of children’s writers everywhere, because those of us who write for the young know that our craft is far more challenging than writing for adults.

True, the occasional B-grade royal or C-grade celebrity may “write a book for children” (usually meaning they had it ghost-written), but the sales of “their” fulsome drivel will usually relate only to the alleged author’s notoriety.

Such works are stereotyped, devoid of intellectual commitment or literary value. No matter, we serious and devoted scriveners keep on engaging young minds, turning on the lights, although I sometimes take a break and write a book for adult readers, if there’s a story there that will feed older minds. The book I describe below is just such a case.

The trapped echidna

Still, I am best known as a writer of non-fiction for children, and it was in that role that I spoke last December at a kids’ lit function, where I described the adventutes I had while rescuing an echidna from a locked drain (the details are set out in chapter 12, but briefly, it involved kneeling on a steel grille, handling a heavy echidna that was grimly gripping a steel ladder, putting me at risk of toppling head-first into a water-filled sump).

The freed echidna

Over coffee afterwards, three friends asked me, separately, and within the space of a couple of minutes, if I was doing a book on echidnas. My answers were, respectively, “Naaah”, “Maybe” and “You betcha!”

My third interlocutor started out by assuming I would say yes, and before I could answer, she had reminded me that most children’s books about echidnas are cloying, saccharine tales of how an anthropomorphic Eddie the echidna couldn’t play with balloons. Those books aren’t about echidnas, they’re about overcoming disabilities, and while that’s socially useful, those books don’t advance understanding or inspire curiosity.

I had already decided that editing a poetry anthology for youngsters and completing a social history of science for oldsters would see me ready to hang up my pen and retire to gardening, leavened by watching noisy action movies and reading Proust, Joyce, P. D. James, Andrea Camilleri and other quality murder mysteries. Instead, I succumbed to peer pressure and launched into this

(Literary social climbers will be pleased to know that Proust and Joyce return in cameo roles in chapter 10, though this may be seen as a cunning ploy to convert certain library costs into tax deductions.)

Going home on the ferry, I started making notes, and I soon realised I would have to read a lot of technical stuff, but there was a story there, waiting to be told, and young readers would like it. Echidnas, spiny anteaters, porcupine anteaters (or Tachyglossus aculeatus if you have my sort of training), have odd quirks. My notes, my initial thoughts, included the following headings, all later went into my planning spreadsheet, and here they are:

* spiky, not at all cuddly;
* not really warm, lay eggs, suckle young:
* many scientific names;
* mainly solitary;
* good diggers (claws!);
* fossils, platypus relatives, Zaglossus;
* Sydney 2000 Olympic mascots: echidna, platypus and kookaburra;
* five-cent coin, postage stamp:
* echidna trains;
* do they drink water?

Over the next fortnight, my plan began to change, because in one week, Christine and I saw four different echidnas, and in the five days around Christmas 2020, we saw three more, and different, echidnas. Then when I started looking at the scientific literature, I realised the really good story was too complex for young readers.

My initial plan for an intellectually honest, stereotype-free, factual book for youngsters had to go on hold. Having declared to friends and family that echidnas (working title) is to be my Last Book, I may still come back to do a simpler version for youngsters, because we still don’t have all the answers, and that’s a good thing for young people (of all ages) to know.

In this book, you will find heaps of technical stuff about physiology, chromosomes, parasites, embryos, membranes, teeth and more. I promise one thing, though: as a children’s writer, I take all the facts, one at a time, and make each give a sound account of itself, but there will only be facts. There will be no flights of fantasy like one I found in Blazing Passion, the book a friend from Project Wombat passed on, complete with this blurb:

…a breathtaking romance that races from the turbulence of nineteenth-century England to the sweltering penal colonies in the Australian jungle…

The book in question was published by Playboy Books, and ‘Stephanie Blake’ is in reality two men who clearly know very little about Australia (“sweltering penal colonies in the Australian jungle”?), but, one assumes, given their publisher, know lots about erotic fantasy. Should you want a copy, Blazing Passion came out in 1978. To save your time, here’s a sample of what passes for dialogue there:

“I’ll fix you up a proper feast. Platypus eggs. Bacon. Sausage and pancakes. And real coffee …”

Actually, I do offer one flight of fantasy later on in the book, but it is clearly fanciful. Finding it is something I leave to the reader, but it’s not the bit about socks full of sea urchins. Those are totally real, and also rate a mention in Sheep.

But that's another story.

Actually, what is a whole 'nother story is that I am resuming control of my out-of-print works and republishing under the Amazon Print-on-demand system.

More on that, later...