accompanied by false starts, controversies,intuition, science politics and the stubborn-ness and enthusiasm innate in we humans.

But there are significant differencesbetween the two books. The Biggest Bangsdetails the early measurements, achieve-ments, false trails and problems that scien-tists faced before afterglows were discovered.Katz is a theoretician who has worked in theGRB field, and he turns a physicist’s eye onthe main astrophysical problems using non-mathematical yet rigorous prose. Often, hewidens the problems encountered in theGRB field to touch on other major riddles in modern astronomy. His explanations are enriched with informative historicallinks. Take, for example, the case of the compactness paradox: GRBs appear to be so small and so luminous that the g-rays weobserve should not be able to escape thesource. In fact, the solution to this conun-drum lies in the properties of the relativisticexpanding fireball, and the foundations for this discovery can be traced back to 1939and the special properties identified in thefluctuating stars called novae, and to the1970s with quasars .

The section of the book describing recentbreakthroughs contains some historicalinaccuracies and is disappointingly short,taking up about a fifth of the book, with onlythree figures. This is too brief to give a properaccount of the observational and theoreticaldevelopments of the past years. For example,although the discovery of the first radioafterglow and its rapid fluctuations aredescribed, there is no discussion of the mostimportant implication of this observation —that it allows the speed of expansion and thesize of the radio source to be measured, andprovides the most elegant and direct proof of relativistic expansion.

These aspects are covered in Flash!, whichdeals primarily with recent discoveries —the X-ray, optical and radio afterglows, theidentification of GRBs as being of cosmo-logical origin and their connection withsupernovae and star-forming regions in distant galaxies. Future missions devoted to GRB observations are also covered.Schilling, a professional science writer, skil-fully leads the reader through the work of scientists in the field, giving a behind-the-scenes view based on interviews with most of the protagonists, and a clear description of the basic concepts behind the theory,observations and instruments. The personalside is somewhat overemphasized, but as awhole the book is an excellent account ofresearch in the field.

Both of these books provide a highlyreadable account of the story of GRBs, andeach in its way is an enlightening and stimu-lating read for the layman. ■

Luigi Piro is in the Istituto Astrofisica Spaziale eFisica Cosmica, CNR, Via Fosso Cavaliere, 00133 Rome, Italy.

Darwin’s personalvoyageFossils, Finches and Fuegians:Charles Darwin’s Adventures and Discoveries on the Beagle,1832–1836by Richard KeynesHarperCollins: 2002. 428 pp. £25

Keith Thomson

“After having twice been driven back by heavysouth-west gales, His Majesty’s Ship Beagle, aten-gun brig, under the command of CaptainFitzRoy, R.N. sailed from Devonport of the27th of December, 1831.” This first sentencefrom Darwin’s The Voyage of the Beagle stillworks its magic. In fact, HMS Beagle, a 90-foot brig re-rigged as a barque, made threemajor surveying voyages: to the coasts ofsouthern South America (1826–30); a returnto South America and then the first completecircle of meridional measurements aroundthe globe (1831–36); and the first full surveyof the coasts of Australia (1837–43).

It was for the second voyage, now knownas the voyage, that Captain Robert FitzRoytook the young Darwin along as a naturalist.FitzRoy originally hoped to share with Darwin authorship of the official Narrative ofthe Surveying Voyages of His Majesty’s ShipsAdventure and Beagle, 1826–1836. But Dar-win preferred to produce his own separateaccount, making a third volume (a fourthconsists of tables and memos). Darwin’s Jour-nal of Researches soon outsold the rest andcontinues in print as The Voyage of the Beagle.

Commentaries on the voyage abound,among the best being Darwin and the Beagleby Alan Moorehead (Hamish Hamilton,1969) and a previous book by Keynes, BeagleRecord (Cambridge University Press, 1979).

Both bring a wealth of supplementary infor-mation and illustrations to the original(Darwin seems never to have got the hang ofusing pictures). Now Keynes has returned tothe subject to re-tell Darwin’s tale in evenmore detail (although the new book is not aswell illustrated and has a modest index).

As is perhaps forgivable in a book by agreat-grandson of Darwin, this is a conven-tional hagiography. There is no hint of any-thing that might reflect badly on Darwin(such as the bitter row with FitzRoy overDarwin’s failure properly to acknowledge inhis book the help of his shipmates) or that iseven mildly controversial. Darwin’s later ill-ness and the argument over why he was onboard in the first place are glossed over. Twomadly giddy letters to Darwin from FitzRoyare presented as if perfectly matter-of-fact,and FitzRoy’s mental breakdown in Chile isdownplayed.

Setting aside the enigmatic genius ofFitzRoy and the tragedy of the Fuegianswhom FitzRoy kidnapped in 1830 andreturned to Tierra del Fuego in 1833, Dar-win’s book continues to fascinate because it isa wonderful read and a source of clues to the‘real’ Darwin and the sources of his ideas.After quitting medical school in Edinburghin 1828, he was accused by his father of caringonly for “shooting, dogs, and rat catching and[you] will be a disgrace to yourself and allyour family”. And in 1831 Darwin graduatedfrom the University of Cambridge with a passdegree, having prepared for the Church. Yetby 1837 he was an acknowledged scientist andalready had the germ of his theory. How didhe use a shipboard library and five years ofexploring, collecting and observing to turnhimself into an intellectual?

The answer is largely that he was no play-boy but a serious young man in search of adefining role. Although Darwin noted in hisautobiography that the voyage was “the most

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On his travels Darwin encountered the Fuegians, depicted here by the Beagle’s artist, Conrad Martens.

© 2002 Nature Publishing Group

important event of my life and has deter-mined my whole career”, he did not reveal,and we still do not know, precisely why andhow. The main unresolved issue concerns the transmutation of species, a subject withwhich Darwin had been familiar since hisstudies in Edinburgh and from his grand-father’s Zoonomia, plus his reading duringthe voyage of Charles Lyell’s Principles ofGeology. Nine months after his return, Darwin wrote that he had started thinkingseriously about the subject in March 1836,when the ship left Australia to start the long(and for Darwin, contemplative) trek home.The immediate triggers were fossils andspecies on the Galapagos Archipelago, whichhe visited in September and October 1835.

Keeping things strictly chronological,Keynes writes brilliantly about what hap-pened when and where, and how Darwinwrote it up in diaries, notebooks and manu-scripts. But there is little mention of theenormous literature on the voyage, and in theend Keynes has not shown us anything newabout the development of Darwin’s philo-sophical thinking on questions of creation ortransmutation over the period from 1831 to1836. The result is a work of great eruditionand a valuable addition to the literature, butthe principal questions remain, as I suspectDarwin always intended, unanswered. ■

Keith Thomson is at the Oxford UniversityMuseum, Parks Road, Oxford OX1 3PW, UK, andis the author of HMS Beagle (W. W. Norton, 1995).

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Leonardo’s layer?A scientific examination of Leonardo da Vinci’sAdoration of the Magi turns up some surprises.Martin KempScience has revolutionized what we can see inpaintings. Non-invasive techniques bear witness to otherwise invisible changes of mind (using X-rays), disclose hidden underdrawings (withinfrared rays), and detect pigments that wereadded to the painting after its completion (throughinfrared and ultraviolet illumination). X-rayfluorescence provides analyses of the inorganicpigments, and photometry measures the spectrumof the reflected light. Gas chromatographyidentifies organic materials such as binding mediaand varnishes from tiny pigment samples, andmicroscopic cross-sections reveal the stratigraphyof the paint and varnish layers.

The new data clearly provide a great resourcefor art historians. However, as with any body ofevidence, we need to learn how to see what issignificant in the visual output and how tointerpret it in the context of other types ofestablished knowledge in the field. Science doesnot provide absolute answers for the art historian,but it allows us to ask ever more complex questionsabout the physical composition of pictures, andpropose solutions with increasing confidence.

The context for these remarks is the excitingevidence beginning to emerge from the technicalexamination of Leonardo da Vinci’s famousAdoration of the Magi (below), which hangs in the

Uffizi Gallery in Florence, Italy. The altarpiece wassubject to a complex agreement with the monks of San Donato a Scopeto in 1481, which decreedthat the painter should receive a portion of thedeceased patron's country property and deposit asum in the Florentine dowry bank in favour of thepatron’s granddaughter. Unhappily, the paintingon the large square panel had not progressedbeyond an underpainting when Leonardo left forMilan, probably in 1482, having also defaulted onhis obligations to the young lady.

Infrared reflectography, which can disclosecarbon-based underdrawing on the white gessopriming, had already revealed more of the subtlebeauties of Leonardo’s touch than is visible on thediscoloured surface of the present picture. Theobvious question arose: should the painting becleaned ? When the possibility was made public,inevitable controversy ensued. Maurizio Seraciniin Florence, who had previously provided theinfrared data, was then asked to undertake a full-scale technical examination.

On my recent visit to Florence, Seracini waskind enough to provide a briefing on what he isdiscovering. The most surprising implicationsarise from his microscopic examination of cross-sections of the paint and varnish layers. As yet these are too scattered to allow definitivejudgements, but his observations indicate that wewill have to revise our thinking about the painting.

The cross-sections suggest that Leonardounprecedentedly laid a semitranslucent layer ofwhite lead over his delicate underdrawing, whichhad been undertaken with a fine brush for itslinear design and a broader brush with dilutedpigment for the shading. On top of this layer headded the central trees, but he abandoned thepicture before completing it with any final strataof fully coloured pigments.

Seracini also questions the authenticity of theheavier brownish layer that begins to establish the background of shadow from which some ofthe figures emerge like ethereal spirits. It seemslikely from the cross-sections that this paint layeris not part of Leonardo’s original structure, notleast because it has seeped into cracks in the lowerstrata — implying that it was added much later.

But nothing is ever simple where Leonardo is concerned. So little is known about the history of the panel for almost 300 years after it was painted that we have no explanatory model forwhen, where, by whom or for what purpose thebrownish pigment might have been added, if itwere not done by Leonardo himself. One questionthat I believe is nearer to an answer is whether thepainting should be cleaned. It looks as if the layersthat are definitely by Leonardo are integrated insuch a complex way with those that might not beby him that we would be well advised at this pointto leave well alone.Martin Kemp is in the Department of the History of Art, University of Oxford, Oxford OX1 2BE, UK.

Science in culture

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