9 For one who endeavours to observe historical facts in the manner here described, it is no mere play of chance that the father of scientific atomism, John Dalton, was by nature colour blind. In fact, colour blindness was known, for a considerable time during the last century, as 'Daltonism', since it was through the publication of Dalton's self-observations that for the first time general attention was drawn to this phenomenon. CHAPTER III The Onlooker's Philosophic Malady In his isolation as world spectator, the modern philosopher was bound to reach two completely opposite views regarding the objective value of human thought. One of these was given expression in Descartes' famous words: Cogito ergo sum ('I think, therefore I am'). Descartes (1596-1650), rightly described as the inaugurator of modern philosophy, thus held the view that only in his own thought-activity does man find a guarantee of his own existence. In coming to this view, Descartes took as his starting-point his experience that human consciousness contains only the thought pictures evoked by sense-perception, and yet knows nothing of the how and why of the things responsible for such impressions. He thus found himself compelled, in the first place, to doubt whether any of these things had any objective existence, at all. Hence, there remained over for him only one indubitable item in the entire content of the universe - his own thinking; for were he to doubt even this, he could do so only by again making use of it. From the 'I doubt, therefore I am', he was led in this way to the 'I think, therefore I am'. 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.