The constant effort to dispel this darkness, even if it fail of success, invigorates and improves the thinking faculty.

If the subjects of human inquiry were once exhausted, mind would probably stagnate; but the infinitely diversified forms and operations of nature, together with the endless food for speculation which metaphysical subjects offer, prevent the possibility that such a period should ever arrive.
It is by no means one of the wisest sayings of Solomon that 'there is no new thing under the sun.' On the contrary, it is probable that were the present system to continue for millions of years, continual additions would be making to the mass of human knowledge, and yet, perhaps, it may be a matter of doubt whether what may be called the capacity of mind be in any marked and decided manner increasing.

A Socrates, a Plato, or an Aristotle, however confessedly inferior in knowledge to the philosophers of the present day, do not appear to have been much below them in intellectual capacity.

Intellect rises from a speck, continues in vigour only for a certain period, and will not perhaps admit while on earth of above a certain number of impressions.
These impressions may, indeed, be infinitely modified, and from these various modifications, added probably to a difference in the susceptibility of the original germs, arise the endless diversity of character that we see in the world; but reason and experience seem both to assure us that the capacity of individual minds does not increase in proportion to the mass of existing knowledge.

(It is probable that no two grains of wheat are exactly alike.