This year marks the 50th anniversary of C P Snow’s famous “two cultures” speech highlighting the gulf between scientists and other intellectuals. In her book The Shadow of the Enlightenment, science historian Theresa Levitt of the University of Mississippi reminds us that such a gap did not always exist and takes us back to a time and a place where science, the arts and even politics were inseparable.

At the beginning of the 19th century, Paris was a place where anything seemed possible. The new revolutionary government had stuttered to a halt, and war with Britain would soon set the stage for Napoleon’s military coup. Writers and artists such as Stendhal and Delacroix would soon shock the establishment with their unflinching portrayals of contemporary society. And in the salons of Paris, writers and politicians were rubbing shoulders with a new breed of intellectuals: the scientists. Spurred on by an arms race with Britain and the industrial revolution, the pace of scientific discovery had quickened. Now, places such as the Academie des Sciences on one side of the Channel and the Royal Institution on the other provided a forum for ambitious young scientists to make their mark and build a career.

All of this helps to explain why the winter of 1806 found two young French scientists, Jean-Baptiste Biot and François Arago, halfway up a Spanish mountain, where they were trying to measure the length of the meridian. Their efforts were aimed at helping define the new Revolutionary unit of length. Unlike the old toise, which was based on the length of the King’s foot, the metre was to be a rational and universal unit, defined as one ten-millionth of the distance along the Paris meridian from the North Pole to the equator.

Elegant though this geometric definition was, the real world was not so accommodating. Shortly after Biot returned to Paris with the measurements, relations between France and Spain soured, and Arago was imprisoned as a French spy. After several months without contact, the Bureau des Longitudes voted to suspend his salary. But Arago managed to escape to Algeria and, after an extraordinary series of adventures, he returned to Paris a year later. Reunited in France, Biot and Arago again became firm friends and close colleagues. This was not to last, however, and Levitt’s book follows the very different trajectories of Biot and Arago as they are driven apart by their competing work in optics, and later by their politics.

Their scientific disagreements focused in particular on the question of colour. Working independently, Biot and Arago had both developed versions of a polarimeter that used a birefringent crystal and a polarizer to generate complex coloured patterns. The question of colour was at the heart of intellectual debate in the 19th century. The Newtonian theory of colour, which held that it was a purely physical property that could be objectively measured, was being challenged by scientists such as Arago, and by artists and dye-makers who sought to try and define a colour standard. The debate often turned on a question more philosophical than physical: do objects have an intrinsic colour that can be measured and defined, or does colour depend on how and by whom it is observed?

This question of perception is the main theme of the book. Levitt links the work of Biot and Arago to the ideological divide in French society between those like Biot, who believed in a natural hierarchy of society with a strong central government, and those like Arago, who believed in the equality of man and government by rational consensus.

Both men continued to carry out groundbreaking work in magnetism (every physics student learns the Biot–Savart law), optics and astronomy, clashing frequently at the Academie des Sciences. Arago eventually became head of the Academie, and to Biot’s horror threw open its doors to the public. In the process, Arago became immensely popular, and entered politics as a champion of the Republican cause. Biot, in contrast, was troubled by the political torment of Paris. With his scientific views out of favour, he retired to the country as a wealthy landowner and mayor. There, he became fascinated with ancient astronomy, which he believed showed that true understanding of the hidden nature of the world could only be obtained by the initiated few.

The style of the book is unusual. In one sense it is a scholarly work on the history of science (complete with comprehensive references), laying out the author’s ideas on the importance of links between the new science of optics and changing concepts of perception in art and politics. But it is also a fascinating biographical tale that sparkles with insights into these turbulent times. As we follow the trials and tribulations of Biot and Arago, Levitt expertly covers a vast range of subjects, from ancient systems of astronomy to the origins of photography and the end of the slave trade. The description of the near-riot as people packed into the Academie des Sciences to see Daguerre present his first photographs is just one example of the many wonderful historical asides.

The Shadow of the Enlightenment is, overall, an enjoyable if dense read. Only a few times in the introduction does the book lapse into academic jargon. Reading it as a scientist rather than a historian, I found the lack of a clear explanation of the science irritating at first; the polarimeter, for example, is never clearly described, and there is no diagram. However, as I read more, I realized that this forced me to see these 19th-century discoveries through the eyes of Biot, Arago and others, peering into the obscurity and trying to make sense of the torrent of new observations and discoveries. Like its subject matter, this fascinating book makes a mockery of the “two cultures” debate, and should appeal to anyone with an interest in the history of science and the origins of the way we see our world.