text:  How then can this law be a guide and a premiss in the investigations of science when those investigations are necessary to complete the proof of the law itself? How can this principle accompany and authorise every step we take in science which itself needs confirmation so long as a process of induction remains to be performed? Or how can this law be established by a series of inductions in making which it has been taken for granted? Objections which wear the air of a quibble have often this advantage--they put our knowledge to the test