His conviction that human thinking ought to remain within the realm of directly experienced observation is shown in the following words: ‘In the solution of natural phenomena, all the length that the human faculties can carry us is only this, that from particular phenomena, we may, by induction, trace out general phenomena, of which all the particular ones are necessary consequences.’⁶ As an example of this he takes gravity, leading the reader from one phenomenon to the next without ever abandoning them, and concluding the journey by saying: ‘The most general phenomena we can reach are what we call laws of nature. So that the laws of nature are nothing else but the most general facts relating to the operations of nature, which include a great many particular facts under them.’