The other conception of human thought reached by the onlooker-consciousness was diametrically opposed to that of Descartes, and entirely cancelled its conceptual significance. It was put forward - not long afterwards - by Robert Hooke (1635-1703), the first scientist to make systematic use of the newly invented microscope by means of which he made the fundamental discovery of the cellular structure of plant tissues. It was, indeed, on the strength of his microscopic studies that he boldly undertook to determine the relationship of human thought to objective reality. He published his views in the introduction to his Micrographia, the great work in which, with the lavish help of carefully executed copper engravings, he made his microscopic observations known to the world.