 By the late 1800s Priestleian Unitarianism, as a tradition of philosophical practice, had died out; academic philosophers, especially those trained in the Scottish school of common sense (the official philosophy taught, for example, by the Unitarians who ran Harvard), knew that the Observations rested on a fundamental mistake; and association psychologists preserved a memory of this precursor of their science. Formal interest in Hartley’s Observations, as a work to be read and pondered, discussed in lectures, written about in articles and books, had collapsed. The last serious engagement with the Observations appears in William James’s Principles of Psychology (1890, 1:553), and even there a casual reader could easily miss it.