"His zeal for science had been stirred at Cambridge by reading Herschel's book on philosophy of science, which had guided his theorising during the voyage.Their discussion is not recorded, but a few months earlier, on 20 February 1836, Herschel had written to Lyell praising his "Principles of Geology" as a work which would bring "a complete revolution in [its] subject, by altering entirely the point of view in which it must thenceforward be contemplated."