As regards his belief in alchemy, Boerhaave was an agnostic: he neither affirmed nor denied the possibility of transmutation. In this respect he resembled Newton and Boyle. Boyle, indeed, was singularly cautious and reticent in his references to alchemistic matters. As was said of him by Shaw, he was too wise to set any bounds to nature: he was not prone to say that every strange thing must needs be impossible, for he saw strange things every day, and was well aware that there are powerful forces in the world of whose laws and modes of action he knew nothing. With that wariness which was habitual to him, he was wont to say that “those who had seen them might better believe them than those who had not”; and he was modest enough to suppose that Paracelsus or Helmont might conceivably know of agents of which he was ignorant. Boerhaave unquestionably spent much time in the study of alchemical works, particularly those of Paracelsus and Helmont, which he repeatedly read. The _Philosophical Transactions_ of the Royal Society contain the results of a laborious but fruitless investigation by him on quicksilver, which he undertook in the hope of discovering the seminal or engendering matter which, on the old theory of the generation of metals, was supposed to be contained in mercury. But although, as he relates, he tortured it by “conquassation, trituration, digestion, and by distillation, either alone or amalgamated with lead, tin, or gold, repeating this operation to 511 or even to 877 distillations,” the mercury appeared only “rather more bright and liquid, without any other variation in its form or virtues, and acquired very little, if any, increase of its specific gravity.”