Perhaps, to the uninformed, it may appear unaccountable that a man should be able to retain in his memory such a variety of learning but the close alliance with each other, of the different branches of science, will explain the difficulty.
Progress, far from consisting in change, depends on retentiveness. When change is absolute there remains no being to improve and no direction is set for possible improvement: and when experience is not retained, as among savages, infancy is perpetual. Those who cannot remember the past are condemned to repeat it. In the first stage of life the mind is frivolous and easily distracted; it misses progress by failing in consecutiveness and persistence. This is the condition of children and barbarians.