  Accordingly, Pascal's preface to the Traité du vide (1651) claims: “the experiments that provide us with an understanding of nature continually proliferate; and, since they are the only principles of physics, their consequences proliferate accordingly” (I, 455). The certainty of experimental results based on observation, their role as principles of a scientific demonstration, and the facility with which natural philosophers could perform appropriate experiments or make relevant observations, led Pascal to an optimistic interpretation of scientific progress. He claimed that, when researchers work together, they “make continual progress in science in proportion as the world gets older” (I, 456). This apparently bright future for physical sciences contrasted with the scientific failure of earlier natural philosophers, “those timid people who did not dare to discover anything in physics” (Preface to the Traité du vide: I, 454) and is reflected in the comment in the Pensées, Fragment 654: “To what extent have telescopes revealed realities to us that did not exist for earlier philosophers?” (II, 807).