Note 161 — Chapter VI · THE LOGICAL CHARACTER OF DESCRIPTIVE SCIENCE

And, again, the intermediate links themselves, however imperceptible, have always to be thought of as exhibiting properties identical in kind with those of objects given in direct presentation. As Mill said, a hypothesis which assumes at once an entirely unfamiliar agent and an equally unfamiliar mode or law of operation, would be useless. Thus the imperceptibles of scientific hypothesis belong essentially to the physical order.