From the centre of that little world as primary, as the initiatory material, my perception of the world of fact widened and widened, by new sights and sounds, by reading and hearing descriptions and histories, by guesses and inferences; my curiosity and interest, my appetite for fact, grew by what it fed upon, I carried on my expansion of the world of fact until it took me through the mineral and fossil galleries of the Natural History Museum, through the geological drawers of the College of Science, through a year of dissection and some weeks at the astronomical telescope. So I built up my conceptions of a real world out of facts observed and out of inferences of a nature akin to fact, of a world immense and enduring, receding interminably into space and time. In that I found myself placed, a creature relatively infinitesimal, needing and struggling. It was clear to me, by a hundred considerations, that I in my body upon this planet Earth, was the outcome of countless generations of conflict and begetting, the creature of natural selection, the heir of good and bad engendered in that struggle. So my world of fact shaped itself. I find it altogether impossible to question or doubt that world of fact. Particular facts one may question as facts. For instance, I think I see an unseasonable yellow wallflower from my windows, but you may dispute that and show that it is only a broken end of iris leaf accidentally lit to yellow. That is merely a substitution of fact for fact. One may doubt whether one is perceiving or remembering or telling facts clearly, but the persuasion that there are facts, independent of one’s interpretations and obdurate to one’s will, remains invincible. 1.4. SCEPTICISM OF THE INSTRUMENT. At first I took the world of fact as being exactly as I perceived it. I believed my eyes. Seeing was believing, I thought. Still more did I believe my reasoning. It was only slowly that I began to suspect that the world of fact could be anything different from the clear picture it made upon my mind. I realised the inadequacy of the senses first. Into that I will not enter here. Any proper text book of physiology or psychology will supply a number of instances of the habitual deceptions of sight and touch and hearing. I came upon these things in my reading, in the laboratory, with microscope or telescope, lived with them as constant difficulties. I will only instance one trifling case of visual deception in order to lead to my next question. One draws two lines strictly parallel; so (two horizontal and parallel lines.) Oblique to them one draws a series of lines; so (a series of parallel and closely-spaced lines drawn through each horizontal line, one series (top) sloping to the right, the other (bottom) to the left)