Discoverers of the Universe: William and Caroline Herschel

The most celebrated astronomer of the 18th century was for the first half of his career a professional musician. And yet not five years into his new vocation, William Herschel, the discoverer of Uranus (which was initially dubbed "George"), was being hailed by Jérôme de Lalande, the French stargazer and writer, as "le plus celebre astronome de tous les astronomes de l'universe". Michael Hoskin's brisk and engagingly written new book is in large part a minute retelling of how this remarkable transformation took place.

But Hoskin's larger subject is really the Herschel family, all of them, across three generations, although the focus in the cluster is the binary system of William (1738-1832) and his sister Caroline (1750-1848).

While William built his increasingly massive telescopes and theorised his way through an astounding series of cosmological hypotheses, Caroline served dutifully as his "assistant". And indeed she was always subservient to her brother, despite the impressive numbers of clusters and comets that she discovered in her own right. In late life, recognised as an honorary Fellow of the Royal Astronomical Society, a member of the Royal Irish Academy and the recipient of various prizes and plaudits, she still insisted on the primacy of her brother's work, in a fashion slightly unnerving to the modern spectator of this very Hanoverian family.

A veteran historian of astronomy, Hoskin has already published several large studies of the Herschels; this book is a popular distillation of much of that authoritative work. Accordingly, scientific analysis is here largely secondary to the drive of biographical narrative. He perhaps plays to the popular gallery a little too much: we are told repeatedly that Newton's Universe was all timeless clockwork, whereas thanks to his discovery of a "natural history" of nebulae, William's was suddenly a biological entity, the sky full of snapshots of the life cycles of the entities populating it.

In his keenness to underscore William's real achievement, Hoskin offers little acknowledgement that this requires a simplification of both Newton's public and private thought, the suppression of any developments between the two men, and silence concerning any 18th-century worldview that differed from the roughly Newtonian model.

William can be a little patronised too by the popular approach: his consistent belief in extraterrestrial life is treated by Hoskin as slightly embarrassing, whereas this was a major debate in the period; and in general anything that looks like religion is largely excluded from serious consideration, an approach historians of science may regret.

Hoskin is, however, such an experienced historian of astronomy that his account and evaluation of the Herschels' technical progress within that discipline is unrivalled. The lightest touches of his prose often disguise heroic labours in the key Herschel archives.

William is revealed as an extraordinary combination of the theorist and the craftsman, as well as "a strange mixture of kindness and selfishness", as Hoskin shrewdly observes. And the rest of the family are there, too: father Isaac, oboist and relentless educator of his children; the dead hand of mother Anna; William and Caroline's brothers, especially Alexander, who with William made many of the Herschels' scientific instruments; and finally William's son John, who repeated his father's work, but for the southern hemisphere.

Above all, we take away from this biography the lively, suggestive detail that Hoskin is so adept at spotting and animating: the young William, teaching his sister to judge angles by cutting cake, or being thrown by his horse and landing with his book still in hand. And at the other end of their lives: Caroline, in Hanover, at the age of 88, entertaining a young relative by scratching her ear with the opposite foot; or singing a catch to the Crown Prince and Princess on her 97th birthday. The catch, needless to say, had been written by William.