Chapter 9 Twilight

  The atoms of Democritus

  And Newton’s particles of light

  Are sands upon the Red Sea shore

  Where Israel’s tents do shine so bright.

  William Blake, 『Mock on, Mock on,

  Voltaire, Rousseau』

  It is inevitable that in a book of this brevity—covering a topic with as long a history and as broad a range of applications as light—many things simply can’t be covered. In particular, the fantastic discoveries arising from looking at other regions of the electromagnetic spectrum than the visible, and the ubiquity of optical devices in everyday life are very incompletely described.

  The myriad versions of imaging devices, from multi-mirror telescopes (with diameters of tens of metres, and adaptively controlled reflectors to null the effects of the twinkling sky) to massive synchrotrons (accelerating electrons to the point that they radiate intense X-rays for looking at tiny material structures, both man-made and natural, to reveal the structure of, for instance,biologically important molecules or engineered metals) are only hinted at. But no matter: I hope that you are convinced of the beauty of light, and that a tour through its mysteries and how they were unravelled is as interesting a story as you could want.

  Meanwhile, the science and technology of optics is vibrant,opening up new areas for exploration and new applications, often with unexpected fruitfulness. Light continues to reveal new mysteries and to inspire new devices: it still engages and fires our imagination as it has done for centuries.