Second Thoughts: When the air blew demons: Alethea Hayter on how the mosaic of A Sultry Month (Robin Clark pounds 6.95) came to her early one morning

FRANCIS THOMPSON once found in a scientific article the perfect image for the moment when an author first sees the shape of a book to come, and he was so excited by it that 'the air blew demons'. According to the scientific article, when musical notes are played over sand, it may form into tree-like patterns. A biographer plays what notes he can over the sands of historical fact, and hopes for that unmistakable moment when the individual grains of sand draw together into a pattern. It happened to me one night in Paris in 1963 as I lay in bed in my Ile St Louis flat, where the blue headlights of passing bateaux mouches on the Seine below my windows cast moving shadows of the riverside poplars across my bedroom ceiling.

Researching a previous book on Elizabeth Barrett Browning, I had been struck by how tightly-knit the London literary world was in the 1840s, and how hindsight and changing values can mislead us today about manners, human relationships, literary reputations taken for granted a century ago. Could one contrive to see these writers as they saw each other, in an interlocked conversation piece? If so, one might, I dared to think, achieve a new sub-genre of biography.

A pattern without a centre, however, would be dull and meaningless. Two things became clear: the period covered must be short, and there must be some striking central event to which all the characters could react. A political crisis? A natural disaster? A literary or artistic scandal? Could all these three combine in some way?

Then I suddenly thought of the suicide of the painter Benjamin Robert Haydon. He had, I remembered, been in touch with Elizabeth Barrett just before he killed himself. I had to get up, then and there at two in the morning, to see what I could find among my books about contemporary reactions to Haydon's death. I scrabbled through index after index in editions of diaries and letters. Yes, Browning and Elizabeth Barrett, though preoccupied with their plans for a secret marriage, had plenty to say about Haydon's death. So had the Carlyles, though they too were having a matrimonial crisis of a different kind. Browning was a friend of the Carlyles; Carlyle had just written to Sir Robert Peel about the Corn Laws repeal crisis, in the midst of which Peel had found time to respond to Haydon's last begging letter. The arabesques of pattern branched back towards the centre; it was like reconstructing a broken mosaic.

Not all the mosaic pieces came together that night. Some of the most vivid fragments - the extraordinary heatwave that month, the grotesque figure of the one-eyed Grafin Hahn-Hahn - came to light in subsequent research. But the main pattern of A Sultry Month was worked out in that sleepless night in which for me too 'the air blew demons'.