have checked their measurements carefully to ensure that the decoupling they observe is real. They have also done the critical com- parison with solid helium-3, for which they expect — and see — no decoupling. Given the nearly atomic dimensions of the Vycor pores, it is hard to imagine that anything other than a superfluid or super- solid could move through them without dissipation. What is less certain is the exact nature of the superflow that Kim and Chan have detected.Although their measurements were done at a pressure of 62 bar, well above the roughly 40 bar needed to solidify helium- 4 in Vycor, it is possible that a disordered, liquid-like layer of helium could have remained near the pore walls. Even if such a layer is responsible for the superflow,its high density and the very small critical velocities observed by the authors imply that it must still be different from the superfluidity previ- ously seen for thin films of liquid helium-4 in Vycor and other porous media. The possible discovery of a new phase of matter, a supersolid, is exciting. The quan- tum-fluids and quantum-solids community can be expected to test the authors’ claims thoroughly, particularly by searching for the persistent currents that are the ‘gold standard’ test of superfluidity. It will be fascinating to see how robust the phenomenon is; can it be seen in other porous media or even in bulk helium? There are enough questions to be answered about the nature and properties of supersolid helium to keep both experimen- talists and theorists busy for a long time. ■ John Beamish is in the Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada. e-mail: beamish@phys.ualberta.ca 1. Kapitza, P. Nature 141, 74 (1938). 2. Allen, J. F. & Misener, A. D. Nature 141, 75 (1938). 3. Osheroff, D. D., Richardson, R. C. & Lee, D. M. Phys. Rev. Lett. 28, 885–888 (1972). 4. Anderson, M. H., Ensher, J. R., Matthews, M. R., Wieman, C. E. & Cornell, E. A. 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No such effect was seen for a Vycor disk empty of helium-4, or when the disk was filled with helium-3. Helium-4 was the first superfluid to be discovered; this might be the first evidence of supersolid behaviour. Temperature Resonant period Empty disk Helium-3 Helium-4 100 YEARS AGO Dr. Nordenskjöld and the members of his South Polar Expedition arrived at Hamburg on January 6. The unexpectedly early return from the South Polar regions of this expedition has, the Times states, enabled Dr. Jean Charcot to recast the plans of the French expedition on board the Français. He now proposes to explore the west coast of Graham Land and to carry out a very exhaustive scientific investigation of that region... It is Dr. Charcot’s definite intention to return at the end of the season of 1904–5. The Français, indeed, is only provisioned for two years, and Dr. Charcot states that if the expedition does not return in the early months of 1905, it must be concluded that they have been involuntarily detained, and a relief vessel must be dispatched to their assistance. From Nature 14 January 1904. 50 YEARS AGO On December 9, the P.E.N. (Poets, Playwrights, Editors, Essayists and Novelists) Club held an informal discussion on poetry and science… At first sight it might appear that these branches of culture had little to do with each other. But Prof. Dingle gave instances of the antagonism between poets and scientists, and pointed out that the overt attacks arising from this antagonism in the past were made by the poets. This, he said, is understandable; at that time it was thought that there was a real external world, the truth about which was being increasingly found out by the scientists. To poets, this world seemed flat and distasteful, but at the back of their minds the uncomfortable thought grew that any alternative was mere illusion. In Prof. Dingle’s opinion, however, there is no need for the poet to harbour such resentment… In fact, science is the organized description of the relations between experiences; poetry, the expression of the experiences themselves. This description of the limits of science, abnegatory as it might seem, did not dispel the injured suspicion of the poets present. Stephen Spender… said that the psychologist may attribute the cause of conscience to infantile experiences; he himself might attribute it to God; what claim had science to the unique truth of the matter? Not only are the findings of science uncomfortable in detail; they are also so complicated that no one man can understand them, and increase of understanding brings with it disorientation and despair. From Nature 16 January 1954. Palaeontology Lost children of the Cambrian Graham E. Budd The initial flowering of animal life on Earth occurred during the Cambrian, some 540–490 million years ago. Fossil embryos from that time can provide clues about the origins of the major animal groups. W hen ancient fossil ‘trilobite embryos’ were reported 1 from China in 1994, the reaction was largely sceptical. After all, biologists had been lamenting (or crowing) for years that fossil embryos could never be found. This bright certainty became mottled with doubts, how- ever, as increasingly convincing material began to appear 2 , the oldest and most con- troversial being some 600 million years old 3 . These fossils raise several questions, to say the least. First, how could they possibly be preserved? Second, why are they concen- trated in a period (600–500 million years ago) that is already unfairly overstocked with exceptionally preserved fossils, such as those of the Burgess Shale in the Canadian Rockies? Third, do they tell us anything about animal evolution? The preservation of these fossils is slowly being recognized as the product of the unusual geochemistry of the transitional ©2004 Nature Publishing Group