On reflection ...

PD Smith explores our fascination with ourselves in Mark Pendergrast's Mirror, Mirror
Mirror, Mirror by Mark Pendergrast
Buy Mirror, Mirror at Amazon.co.uk

by Mark Pendergrast 404pp
Basic Books, £19.99

Your reflection follows you from the cradle to the grave. For Sylvia Plath, writing in 1961, the mirror was a cold companion on life's journey: "I am silver and exact. I have no preconceptions./ Whatever I see I swallow immediately/ Just as it is, unmisted by love or dislike./ I am not cruel, only truthful-/ The eye of a little god, four-cornered."

Yevgeny Zamyatin's remarkable dystopian novel We, written in 1920, is set in a city-state made entirely of glittering glass. In this future world the human soul has been abolished, but the narrator is displaying worrying symptoms. A medic confirms his fears: he has a soul. To explain this concept, the doctor uses a mirror metaphor: "Just imagine that through the application of some form of fire this impenetrable surface has suddenly softened ... everything penetrates it, into that mirror-world which we eyed with such curiosity when we were children."

In the pre-Christian era, the Etruscan word for soul, hinthial, also meant an image reflected in a mirror. By the 12th-century, theologian Peter Lombard was comparing the soul to "a mirror in which in some way we know God". For millennia, mirrors have beguiled and mystified us. Who hasn't stood between two mirrors and tried to glimpse infinity in the endless recession of reflections? Mark Pendergrast's excellent cultural and scientific history of the mirror is also a "history of looking" and tells the story of our quest for self-knowledge in the silvered glass. The earliest mirrors were polished obsidian, dark natural glass, "melted in volcanic hearts". Ancient peoples buried their dead with mirrors, believing them to be receptacles for the soul. A richly ornate mirror was found in the tomb of Tutankh-amen. The Egyptian symbol for life, the ankh, looks like a mirror, "egg-shaped, with a T-handle attached at the small end". Its name was ankh-en-maa-her, meaning "life-force for seeing the face", which was shortened to just "see-face": maa-her.

Our fascination with mirrors begins at about 20 to 24 months old, when we first recognise ourselves in a reflective surface. Simultaneously we learn to say "I" and "me". Being able to use a mirror is part of our essential reflexivity as human beings. According to primatologist Frans de Waal, "without self-awareness we might as well be folkloric creatures without souls, such as vampires, who cast no reflections". Chimps and dolphins are among the very few animals that are able to recognise themselves in a mirror. The ancient Romans used mirrors to spice up their orgies, much to the disgust of the stoical Seneca. According to Pendergrast, dolphins too find mirrors sexually stimulating: "Their libido went wild," he reports, and "they assumed positions so that they could watch themselves in the mirror."

For his history of reflection, Pendergrast digs deep into religion, folklore, literature, art, magic and science. He unearths some wonderful stories, such as how the sun king, Louis XIV, broke the Venetian mirror-making monopoly in the 17th century ("one of the world's first acts of industrial espionage"). A key element in his story is light: "that mysterious medium that acts simultaneously like a wave and a particle, imposes a speed limit on the universe and in a sense is the universe". Plato said our eyes contained "so much of fire as would not burn, but gave a gentle light". Visual rays streamed from our eyes, he thought, a wrong-headed notion that would dominate the study of light for a thousand years. Even in 2002, a poll revealed that more than half those asked still thought Plato was right.

In the 16th century, "scryers" tried to divine the future by gazing into reflective surfaces. Queen Elizabeth's favourite was Dr John Dee. His "Shew-stones" were an Aztec obsidian mirror and crystal balls, but his contemporary, Nostradamus, preferred a bowl of water supported on a bronze tripod. In the story of Snow White, the evil queen uses a mirror for her scrying. Ancient Egyptians, Hebrews and Chinese all practised this mystic craft and "prepubescent Vedic Indian girls could see the future in a mirror or spoonful of water". But child scryers often lost their sight - not from glimpsing the fearsome face of god, but from staring into the blinding light.

Today, astronomers don't claim to see the future, but they do use mirrors to travel back through time, as their optics snare the light of ever more distant stars. According to Dan Goldin of Nasa, "large mirrors are to astrophysics and astronomy what computational speed is to computing ... the bigger the mirrors are, the deeper we can stare." Pendergrast admires the dedication of these scientific mirror makers.

The "brilliant, egotistical optician" George Willis Ritchey spent five years polishing the glass for the 100in mirror of the Mount Wilson Observatory near Pasadena, which in 1919 was the world's largest. Its mirror showed a perfect paraboloid curve to within 0.000003 of an inch. Marcus Brown, who was in charge of polishing the 200in mirror at Mount Palomar in the 1930s, told his assistants: "Glass won't ever do what you expect. It has as many moods as a movie star." Nasa learnt that lesson the hard way. Its "Great Optical Device" (GOD), aka the Hubble Space Telescope, was hailed as having "the most precise large mirror ever made". In fact it turned out to have a spherical aberration: "The mirror did indeed feature the most perfectly polished surface ever produced, but its shape was perfectly wrong."

Pendergrast's book is a testament to the power of mirrors to enthral, and John Dobson's experiences show that they are as beguiling as ever. After working on the Manhattan Project building the atomic bomb, Dobson joined a San Franciscan Vedanta monastery in 1944. The first mirror he ground by hand was originally a porthole glass. When fitted into a cardboard tube together with the eyepiece from old binoculars, the view it gave him of the moon took his breath away.

He was thrown out of his monastery in 1967 for star gazing, but by then he had a new vocation: astronomy. Dobson founded the Sidewalk Astronomers, setting up his hand-made telescopes at the corner of Jackson and Broderick Streets in San Francisco for anyone to use. "People ask why we are doing it," he says. "Because nobody else will. I go out of my way to help other people see where the hell they got born. We are the dust of exploded stars." Like Dobson, Pendergrast wants to enlighten us and "untarnish our mirrors". One thing's certain - you'll never look at yourself in quite the same way again.

· PD Smith's illustrated biography of Einstein is published by Haus.