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exhibiting a similar luminosity, such as minerals and salts would show similar properties. It was, in fact, a hint (намек) of Henri Poincare (1854-1912) that had caused Becquerel to find out whether there was any connection between X-rays and phosphorescence. Becquerel's father had made a magnificent collection of phosphorescent substances. *Had Becquerel selected zinc sulphide from this collection, the discovery of the phenomena of ra­dioactivity might have been delayed for another fifty years, but here was something like a real accident in the history of science again. He selected uranium salt and he saw that it did show the properties of radioactiv­ity. The new mysterious rays from uranium were also capable of penetrating matter, and they were produced without any apparatus, spontaneously, from apparently inert and permanent chemicals.

This was an ever greater shock to the physical and chemical ideas of the nineteenth century. This was a shock to the doctrine of the conservation of energy. Where did the energy which was so apparent in these new radioactive compounds come from? It could only come from within the atom itself. An almost infinitesimal amount of radioactive material gave off appreciable amounts of energy. This implied that energy was con­tained in the atom in the quantities undreamt of by the users of the energies.

Once radioactivity was discovered scientific progress was fast - much faster, indeed than in any earlier period in the history of science. Within six years Pierre Curie (1859-1906) and his Polish wife Marie Curie (1867-1934) found sources very much stronger than the original ura­nium. They isolated elements of a new kind such as polonium and radium, the latter so powerful that it shone by itself in the dark and could inflict serious and fatal injuries fmdsanz] (вред) on people who went near it.