This paper claims that one way to bridge the gap between Francis Bacon’s speculative philosophy and his natural historical and experimental investigations is by looking at his peculiar top-down strategy of measuring Nature. Key to this strategy is the construction of perceptive instruments, i.e., devices “subtle enough” to detect and map natural limits, powers and virtues. In this paper, I discuss some of Bacon’s ideas for the development of perceptive instruments, and I show how his particular investigative strategy leads to (...) the construction of an interesting and insufficiently investigated operational vocabulary. I focus on two particular terms of this vocabulary, “orbs of virtue” and “perception.” I show that, although originating in a natural-philosophical context, both terms acquire new, operational meanings in Bacon’s late natural histories. They vindicate the use of instruments and provide the necessary tools for a complex and interesting top-down approach to measuring Nature. (shrink)