"Hardly twenty years after the English artificer, Robert Norman, had in 1576, devised the inclinatorium, which enabled him to determine the dip or inclination of the magnetic needle, Gilbert boasted that, by means of this instrument, he could ascertain a ship's place in dark starless nights. Gilbert commends the method as applicable aere caliginoso [dark atmosphere]; and Edward Knight, the English mathematician, in the introduction which he added to his master's great work, describes this proposal as "worth much gold." Having fallen into the same error with Gilbert of presuming that the isoclinal lines coincided with the geographical parallel circles, and that the magnetic and geographical equators were identical, he did not perceive that the proposed method had only a local and very limited application."