Considering the herculean task in which they were engaged for so many years, we scarcely know which to admire most, their clearness of vision, which made them divine success; their profound knowledge, which guided them in the choice of reagents; or the indomitable perseverance which characterized them in their laborious task and in the countless sacrifices which they were obliged to make before their efforts were crowned with success. During this long search into the inner heart of nature, Pierre Curie was often so discouraged and depressed that, had he not been sustained by his more sanguine wife, he would time and again have given up his investigations in despair. But Marie Curie never faltered. She never lost faith in their theories or confidence in the outcome of their great undertaking. Before her deft hands and fertile brain difficulties vanished as if under the magic wand of Prospero. At length, after countless experiments of the most delicate character, after bringing to bear on the solution of the problem before them the most refined methods of chemical analysis, they were rewarded by one of the most extraordinary discoveries recorded in the annals of science. With the announcement of the discovery of radium, the Curies sprang into world-wide fame, and the name of the wonderful woman who had been the prime mover in the supreme achievement was on every lip. Pierre Curie himself declared that more than half of the epochal discovery belonged to his wife. It was she who began the work. It was she who, after her marriage, enlisted in it the cooperation of her husband. It was she whose invincible patience and persistence--typical of the noblest representatives of her race--supported him during periods of doubt and despondency and fanned his flagging spirits to new endeavor. It can indeed be truthfully asserted that had it not been for her penetrating intelligence, her tenacity of purpose and her keenness of vision, which were never at fault, the great victory which crowned their efforts would never have been achieved.[160] Compare their work with that which was accomplished by their illustrious predecessors, Antoine Laurent Lavoisier, and his wife, a century earlier. The latter, by their discovery of and experiments with oxygen, were able to explain the until then mysterious phenomena of combustion and respiration and to coordinate numberless facts which had before stood isolated and enigmatic. But the reverse was the case in the discovery of that extraordinary and uncanny element, radium. It completely subverted many long-established theories and necessitated an entirely new view of the nature of energy and of the constitution of matter. A substance that seemed capable of emitting light and heat indefinitely, with little or no appreciable change or transformation, appeared to sap the very foundations of the fundamental principle of the conservation of energy.