The degree of probability that a certain event will take place may increase in proportion to the number of times that we have seen a similar event take place in the past. “Thus a man’s having observed the ebb and flow of the tide today, affords some presumption, though the lowest imaginable, that it may happen again tomorrow: but the observation of this event for so many days and months, and ages together, as it has been observed by mankind, gives a full assurance that it will.”1 It is this sort