The delight of observation, which began in childhood, continued to old age, and increased instead of weakening. When he was fatigued and worn with writing and theorizing, when illness tormented him and weakness rendered more concentrated effort impossible, it was a relief to turn to the simple contemplation of facts, and the budding and fading of flowers and the varied activity of insects offered at all times diversion and contentment. Sometimes he dwells upon the larger aspects of such contemplation, the joy of discovery, the excitement of finding what has never been found before. Again and again in his southern voyages this excitement appears: ‘In these wild countries it gives much delight to gain the summit of any mountain. There is an indefinite expectation of seeing something very strange, which, however often it may be balked, never failed with me to recur on each successive attempt.’[22] Or the pleasure may come in what seem the humblest, smallest things, in what is to ordinary persons negligible, or even repulsive. One of Darwin’s most attractive books, perhaps with ‘The Expression of the Emotions,’ the most attractive from the casual reader’s standpoint, is that in which he gathers together the results of his study of earthworms, a study which had continued through years of patient and thoughtful investigation of a subject which, even from the naturalist’s point of view, would not seem one of the most fruitful or engaging. The fundamental principal of all scientific observation is accuracy, and no one knew this better than Darwin. No one understood better than he the subtle, treacherous influences that are always at work, distracting, impairing, and distorting exact and lucid vision. There is the danger of seeing what we are accustomed to see and therefore think we see. There is the danger of seeing what others have seen and described before us. There is the supreme danger of seeing what we wish to see, what accords with some preconceived theory or dogma. Against all these dangers Darwin tried to be ever on his guard, and he is constantly warning others of them and emphasizing the importance of pure accuracy and the enormous difficulty of it. ‘Good heavens, how difficult accuracy is!’[23] Among all the merits of the scientist he values accuracy highest, the instinct and the ability to record facts correctly: ‘I value praise for accurate observation far higher than for any other quality.’[24] And especially in one admirable passage he stresses and reiterates both the difficulty and the value: ‘Accuracy is the soul of Natural History. It is hard to become accurate; he who modifies a hair’s breadth will never be accurate.... Absolute accuracy is the hardest merit to attain, and the highest merit.’[25]