[Footnote 12: You behold here, traveller, the bust of Nicholas Steno as it was set up by more than a thousand scientists from all over the world, as a memorial to him, on the fourth of the Kalends of October, 1881. The geologists of the world, after their meeting in Bologna, under the presidency of Count John Capellini, made a pilgrimage to his tomb, and in the presence of the chosen representatives of the municipality, and of the learned professors of the University, honored the mortal ashes of this man, illustrious among geologists and anatomists.] {161} Stensen's work brought him in contact with some of the distinguished men of the seventeenth century, all of whom learned to appreciate his breadth of intelligence and acuity of judgment. We have already mentioned his epistolary relation with Spinoza, and have said something about the controversy with Leibnitz, into which, in spite of his disinclination to controversy generally, he was drawn by the circumstances of the time and the solicitation of friends. Another great thinker of the century with whom he was brought into intimate relationship was Des Cartes, the distinguished philosopher. In fact, Des Cartes's system of thought influenced Stensen not a little, and he felt, when describing the function of muscles in the human body, and especially when he demonstrated that the heart was a muscle, that the mechanical notions he was thus introducing into anatomy were likely to prove confirmatory of Des Cartes's philosophic speculations. Almost more than any other, Stensen was the father of many ideas that have since become common, with regard to the physics of the human body and its qualities as a machine. With his breadth of view, from familiarity {162} with the progress of science generally in his time, Steno's discussions of the reason for the lack of exact knowledge and for the prevalence of error, in spite of enthusiastic investigation, are worth while appreciating. He considered that the reason why so many portions of natural science are still in doubt is that in the investigation of natural objects no careful distinction is made between what is known to a certainty and what is known only with a certain amount of assurance. He discusses the question of deductive and inductive science, and considers that even those who depend on experience will not infrequently be found in error, because their conclusions are wider than their premises, and because it only too often happens that they admit principles as true for which they have no sure evidence. Stensen considered it important, therefore, not to hurry on in the explanation of things, but, so far as possible, to cling to old-time principles that had been universally accepted, since nearly always these would be found to contain fruitful germs of truth.